Vessel Maneuvering and Handling

Environmental forces that affect the motion of a vessel are wind, seas, and current. The coxswain has no control over them and must take the time to observe how the wind, seas, and current, alone and together, affect the vessel. The coxswain should also determine how these forces cause the vessel to drift, and at what speed and angle. Coxswains must use environmental forces to their advantage and use propulsion and steering to overcome the environmental forces. Usually, a good mix of using and overcoming environmental forces results in smooth, safe boat handling.

The wind acts upon any portion of the vessel that is above the waterline. This includes the hull, superstructure, and on smaller boats, the crew. The amount of surface upon which the wind acts is called sail area. The vessel will make “leeway” (drift downwind) at a speed proportional to the wind velocity and the amount of sail area. The “aspect” or angle the vessel takes due to the wind will depend on where the sail area is centered compared to the underwater hull’s center of lateral resistance. A vessel with a high cabin near the bow and low freeboard aft (see Figure 6-1) would tend to ride stern to the wind. If a vessel’s draft were shallower forward than aft, the wind would affect the bow more than the stern. A sudden gust of wind from abeam when mooring a vessel like this might quickly set the bow down on a pier.

[Illustration in the handbook: Figure 6-1 — High Cabin Near Bow, Low Freeboard Aft]

Knowledge of how the wind affects a vessel is very important in all close quarters situations, such as mooring, recovery of an object in the water, or maneuvering close aboard another vessel. If maneuvering from a downwind or leeward side of a vessel or pier, the coxswain should look for any wind shadow the vessel or pier makes by blocking the wind (see Figure 6-2). The coxswain should also account for the change in wind by planning maneuvers with this wind shadow in mind.

[Illustration in the handbook: Figure 6-2 — Wind Shadow]

Seas are a product of the wind acting on the surface of the water. Seas affect boat handling in various ways, depending on their height and direction and the particular vessel’s characteristics. Vessels that readily react to wave motion, particularly pitching, will often expose part of the underwater hull to the wind. In situations such as this, the bow or stern may tend to “fall off” the wind when cresting a wave, as less underwater hull is available to prevent this downwind movement. Relatively large seas have the effect of making a temporary wind shadow for smaller vessels. In the trough between two crests, the wind may be substantially less than the wind at the wave crest. Very small vessels may need to make corrective maneuvers in the trough before approaching the next crest.

Current acts on a vessel’s underwater hull in the same manner as wind pushes on a vessel’s superstructure. The amount of draft a vessel has will determine how much affect current will have. A strong current will easily move a vessel upwind.

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A one-knot current may affect a vessel to the same degree as a 30-knot wind. The coxswain should learn to look for the signs of current flow so as to be prepared when current affects the vessel, and should be particularly aware of instances where current shear is present. As with wind, a large, stationary object like a breakwater or jetty will cause major changes in the amount and direction of current (see Figure 6-3). Crewmembers should note the amount of current around floating moorings or those with open pile supports. Caution should be used when maneuvering in close quarters to buoys and anchored vessels. Crewmembers should observe the effect of current by looking for current wake or flow patterns around buoys or piers and should watch how currents affect other vessels.

[Illustration in the handbook: Figure 6-3 — Effects of Current]

Environmental conditions can range from perfectly calm and absolutely no current to a howling gale and spring tides. Chances are that even if operation does not occur at either extreme, some degree of environmental forces will be in action.

The coxswain should know how the vessel responds to combinations of wind and current, and should determine which one has the greatest effect on the vessel. It may be that up to a certain wind speed, current has more control over a given vessel, but above that certain wind speed, the boat sails like a kite. The coxswain should know what will happen if a sudden gust of wind is encountered; will the boat immediately veer, or will it take a sustained wind to start it turning? When current goes against the wind, the wave patterns will be steeper and closer together. The coxswain should be particularly cautious where current or wind is funneled against the other. Tide rips, breaking bars, or gorge conditions frequently occur in these types of areas and may present a challenge to even the most proficient coxswain. On the other hand, making leeway while drifting down current requires a change in approach to prevent overshooting the landing.

NOTE

Stay constantly aware of conditions, how they may be changing, and how they affect the vessel.

For this discussion of propulsion, the following assumptions are made:

(01) If a vessel has a single-shaft motor or drive unit, it is mounted on the vessel’s centreline, (02) When applying thrust to go forward, the propeller turns clockwise (the top to the right or a “right-handed” propeller), viewed from astern, and turns counterclockwise viewed from astern when making thrust to go astern, (03) If twin propulsion is used, the propeller to starboard operates as above (right-hand turning), while the port unit turns counterclockwise when making thrust to go forward when viewed from astern (left-hand turning) (see Figure 6-4), (04) Be aware that some propeller drive units rotate in only one direction, and changing the propeller blade angle of attack controls ahead or astern thrust (controllable pitch propeller).

[Illustration in the handbook: Figure 6-4 — Twin Propulsion]

The key to powered vessel movement is the effective transfer of energy from the source of the power (an internal combustion engine) to the water through a mechanism that turns the engine’s power into thrust. This thrust moves the boat. There must also be an element of directional control, both fore and aft, and from side to side. Propulsion and steering are considered together here for two reasons. Applying thrust has no use if the vessel’s direction cannot be controlled, and often the device providing the propulsion also provides the steering. There are three common methods to transfer power and provide directional control:

(01) Rotating shaft and propeller with separate rudder, (02) A movable (steerable) combination as an outboard motor or stern drive, (03) An engine-driven pump mechanism with directional control, called a waterjet.

All three arrangements have their advantages and disadvantages from the standpoint of mechanical efficiency, ease of maintenance, and vessel control. Using one type of propulsion instead of another is often a matter of vessel design and use parameters, operating area limitations, life cycle cost and frequently, personal preference. There is no single “best choice” for all applications. Regardless of which type you use, become familiar with how each operates and how the differences in operation affect vessel movement. On almost every boat, propulsion and steering arrangement is designed to operate more efficiently and effectively when going ahead than when going astern. Also, every vessel rotates in a transverse

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direction about a vertical axis on its pivot point (see Figure 6-5). The fore and aft location of the pivot point varies from boat to boat, but is generally just forward of amidships when the boat is at rest. As a hull moves either ahead or astern, the effective position of the pivot point moves either forward or aft, respectively.

[Illustration in the handbook: Figure 6-5 — Pivot Point]

In small craft installations, the propeller shaft usually penetrates the bottom of the hull at an angle to the vessel’s designed waterline and true horizontal. The practical reason for this is because the engine or marine gear must be inside the hull while the diameter of the propeller must be outside and beneath the hull. Additionally, there must be a space between the propeller blade arc of rotation and the bottom of the hull. For single-screw vessels, the shaft is generally aligned to the centerline of the vessel. However, in some installations, a slight offset (approximately 1°) is used to compensate for shaft torque. To finish the installation, the rudder is usually mounted directly astern of the propeller. For twin-screw vessels, both shafts are parallel to the vessel’s centerline (or nearly so), rudders are mounted astern of the propellers, and the rudders turn on vertical rudder posts.

When rotating to move in a forward direction, a propeller draws its supply of water from every direction forward of and around the blades. Each blade’s shape and pitch develop a low-pressure area on the forward face of the blade and a high-pressure area on the after face of the blades, forcing it in a stream toward the stern. This thrust, or dynamic pressure, along the propeller’s rotation axis is transmitted through the shaft, moving the boat ahead as the propeller tries to move into the area of lower pressure.

Regardless of whether the propeller is turning to go ahead or astern, the water flow pattern into the propeller’s arc of rotation is called suction screw current, and the thrust flow pattern out of the propeller is called discharge screw current (see Figure 6-6). The discharge screw current will always be stronger and more concentrated than the suction screw current.

[Illustration in the handbook: Figure 6-6 — Screw Current]

In addition to the thrust along the shaft axis, another effect of propeller rotation is side force. Explanations for side force include:

(01) How the propeller reacts to interference from the vessel hull as the hull drags a layer of water along with it (the propeller encounters boundary layer “frictional wake”), (02) How the discharge screw current acts on the rudder, (03) The propeller blade at the top of the arc transfers some energy to the water surface (prop wash) or to the hull (noise) and that the blade at the top of the arc either entrains air or encounters aerated water.

Due to the angle of the propeller shaft, the effective pitch angle is different for ascending and descending propeller blades, resulting in an unequal blade thrust. The descending blade has a higher effective pitch angle and causes more thrust. This net effect is sometimes referred to as sideways blade pressure. The important facts to know: for a right-handed propeller turning ahead, the stern will tend to move to starboard (see Figure 6-7), and for a right-handed propeller when backing, the stern will tend to move to port. For a left-handed propeller (normally the port shaft on a twin-screw boat), the action is the opposite. An easy way to remember how side force will push the stern is to think of the propeller as a wheel on the ground. As the wheel rolls clockwise, it moves to the right. As a propeller turns clockwise when viewed from astern, the stern moves to starboard.

[Illustration in the handbook: Figure 6-7 — Side Force]

Cavitation is the rapid formation and collapse of vapor pockets in a flowing liquid in regions of very low pressure, and is a frequent cause of structural damage to propellers. Cavitation usually occurs when the propeller rotates at very high speed and a partial vacuum forms air bubbles at the tips of the propeller blades. Cavitation can also occur when trying to get a stopped propeller to spin at maximum speed, rapidly going from ahead to astern (or vice-versa), or by operating in aerated water where bubbles are dragged into the propeller flow. Cavitation occurs more readily when backing, as the suction screw current draws water from behind the transom, and air at the waterline mixes with the water and is drawn into the propeller. Cavitation frequently occurs when backing with outboard motors. In this case, through-hub exhaust gas bubbles are also drawn forward into the propeller blade arc.

NOTE

[Illustration in the handbook: Figure 6-8 — Effect of Rudder Action]

Outboard motors and stern drives will be considered together, as both include a pivoting gear case and propeller drive unit (called a lower unit on an outboard). The differences between these drive arrangements and the shaft/propeller/rudder arrangement is that the screw currents and thrust from an outboard or stern drive can be developed at an angle to the vessel centerline. Also, the point where thrust and steering are developed is usually aft of the vessel hull. The lower unit contains drive gears, a spline connection, and on many set-ups, through-the-propeller hub exhaust. Many lower unit gear housings are over six inches in diameter. Where an inboard engine powers the stern drive attached through the transom to the drive unit (the outdrive) and is commonly referred to as an inboard/outdrive or I/O. The outboard “powerhead” (engine) is mounted directly above the lower unit. Both outboards and stern drives can usually direct thrust at up to 35° to 40° off the vessel centerline. Also, both types generally allow the coxswain some amount of trim control. Trim control adjusts the propeller axis angle with the horizontal or surface of the water. This is done by operating the vessels trim/tilt or trim tab controls. Effectively operating the trim/tilt or trim tabs will reduce the amount of the vessels surface that is actually in contact with the water. Balancing a vessel properly along its axis fore and aft, while keeping it on an even keel is called “trim.” Efficiently operating trim control can improve fuel consumption, increase speed, and reduce the effects of porpoising. Porpoising is a continuous rise and fall of the bow in a rhythmic pattern. Contributing causes of porpoising are weather, load distribution, and power (thrust). Porpoising is a condition more commonly found in faster performance boats. The major difference in operation between the I/O and outboard is that the outboard motor, operating with a vertical crankshaft and driveshaft, develops a certain degree of rotational torque that could cause some degree of “pull” in the steering, usually when accelerating or in a sharp turn to starboard. If caught unaware, the coxswain could have difficulty stopping the turning action. The easiest way to overcome this torque-lock is to immediately reduce RPMs before trying to counter-steer.

Outboards and stern drives have a small steering vane or skeg below the propeller. The housing above the gearcase (below the waterline) is generally foil shaped. Though these features help directional control, particularly at speed, the larger amount of steering force from an outboard or stern drive is based upon the ability to direct the screw discharge current thrust at an angle to the vessel’s centerline (see Figure 6-9).

This directed thrust provides

extremely effective directional control when powering ahead. When making way with no propeller RPMs, the lower unit and skeg are not as effective as a rudder in providing directional control.

[Illustration in the handbook: Figure 6-9 — Lower Unit/Outdrive Directed Thrust]

The propeller forces discussed above in A.11 Propeller Action also apply to the propellers on

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outboards or outdrives. However, because these drives can be directed, side force can be countered. The steering vane/skeg angle is usually adjustable, also assisting in countering side force.

When backing, it is possible to direct outboard/outdrive thrust to move the stern to port or starboard. When backing with the unit hard over to port, propeller side force introduces an element of forward motion (Figure 6-10), but can be countered through less helm. When backing to starboard, the side force tends to cause an element of astern motion and also tries to offset the initial starboard movement. Many lower units are fitted with a small vertical vane, slightly offset from centerline, directly above and astern of the propeller. This vane also acts to counter side force, particularly at higher speeds.

[Illustration in the handbook: Figure 6-10 — Lower Unit/Outdrive Side Force]

Outboards and stern drive usually allow a level of vertical thrust control. Trim controls the angle of attack between the propeller’s axis of rotation and both the vessel waterline and the surface of the water. Vertical thrust control, especially applied aft of the transom, changes the attitude the vessel hull will take to the water (Figure 6-11). Small amounts of trim should be used to offset for extreme loading conditions or to adjust how the vessel goes through chop.

[Illustration in the handbook: Figure 6-11 — Trim to Offset Loading Condition]

In addition to trim, a vertical component of thrust develops in another situation. Depending on the type of hull, if a vessel is forced into an extremely tight turn with power applied, thrust is directed sideways while the vessel heels, actually trying to force the transom up out of the water, causing a turn to tighten even more. In lightweight or highly buoyant outboard powered boats, use of full power in tight turns can cause loss of control or ejection of crew, coxswain or both. It is mandatory that the helmsmen attach the engine kill switch lanyard to themselves.

Trim tabs consist of two adjustable planes mounted at the bottom edge of the transom where the planning surface meets the water. Controlled by a hydraulic power unit, these tabs can move up and down when adjusted by the vessel operator. They provide lift in order to compensate for changes in speed, weight distribution, and sea conditions.

Trim tabs control the pitch and roll axis of a vessel and have three specific purposes: performance, efficiency, and safety. They provide performance by reducing pounding, correct listing, eliminating porpoising, and offset propeller torque. They increase efficiency by reducing fuel consumption, reducing engine laboring, and eliminate squatting. Furthermore, they increase safety by reducing wake size, improve vessel handling, and reduce stress on the hull.

For the best results from your trim tabs, operate them in short half-second “bursts” and let the boat react before making another adjustment. The amount of time between corrections is influenced by the size of the trim tabs and the boat’s speed. When they are adjusted downward, the water force on the trim tab creates upward pressure (lift), raising the stern and reducing hull resistance (drag). The surface area of the tab, the angle of deflection, and the speed of the boat all contribute to greater lift. Operating your trim tabs in this manner will help avoid over-trimming, which occurs when you have deflected the tabs too far. Over-trimming while operating at high speeds creates unpredictable boat handling, which results in an extremely hazardous condition.

Trim tabs assist in getting the vessel up on plane around the pitch axis (Figure 6-12) as quickly as possible. Once achieved, it easy to maintain the boat’s most economical cruising speed. This is accomplished by simultaneously lowering both trim tabs. The force of the water against them will push the stern up consequently lowering the bow. Trim tabs may also be used to keep the bow up to avoid taking seas over the bow if the water is rough. The trim tabs can be adjusted to keep the bow from digging into waves or prevent launching the boat over waves. The vessel operator would simultaneously raise both trim tabs, causing the stern to lower and the bow to rise.

As a result of uneven weight distribution (e.g. passenger or excess gear), propeller torque or wind, a vessel can run with a list. Running with a list is uncomfortable, as well as unsafe. The port and starboard trim tabs act independently, making them an excellent instrument to provide effective list correction. To do this, adjust the trim tab downward on the listing side using short bursts. The water pressing against the tab as you move will lift that side of the vessel around the roll axis (Figure 6-12) and eliminate your list.

NOTE

Trim tabs will have less effect at slower speed than at high speed.

[Illustration in the handbook: Figure 6-12 — Pitch and Roll Axis]

Power trim can be used to adjust the boat’s pitch axis, but it is highly inefficient. This is because a propeller is designed to force the boat forward. When utilizing your engines power trim, the propeller must not only push the boat forward but raise the stern as well. In this situation, propeller slippage is greatly increased thereby wasting RPMs. Power trim also cannot correct listing, and is ineffective at slower speeds. For increased speed and power, use your trim tabs in conjunction with your engine trim. The trim tabs adjust how your vessel plane, while the power trim adjusts the propeller. The result is optimum performance and efficiency not attainable by the use of the engine power trim alone. To achieve maximum performance:

(01) Adjust the trim tabs to achieve a planing efficiency, (02) Then use the engine trim to position the propeller path parallel to the water flow, (03) If necessary, re-adjust the trim tabs to “fine tune”.

the bow down so the sharp forward sections of the boat do their work splitting the waves. This will bring the “V” of the hull in contact with the waves rather than having the wave’s pound the hull.

For best maneuverability and maximum steering control, trim tabs should be fully raised in a following sea. Keep the trim tabs up so the tide or current won’t push the stern from side to side.

When operating in astern propulsion, both trim tabs should be fully raised. The trim tabs produce drag if they are left down. This puts strain on the tabs as well as affects the boat’s handling. Additionally, if one tab is lowered more than the other while operating astern the boat tends to pivot around the lowered tab.

As speed increases, the bow repeatedly rises out of the water until gravity overcomes lift and the bow bounces down. Trimming down in half second bursts will allow the trim tabs to deflect, thus resulting in the porpoising to subside and your speed should remain the same or increase. Only a slight amount of trim tab adjustment should be necessary.

Jacking plates are used on smaller boats, usually less than 30ft in length, to aid in operating in shallow water. Instead of being mounted directly to the transom, the outboard motors are mounted to the jack plate which can be raised or lowered as needed (Figure 6-13).

[Illustration in the handbook: Figure 6-13 — Jacking Plate]

Jacking plates, when equipped, can raise the outboard motors allowing you to control the engine draft. By raising the jacking plates and applying throttle, you can get on a plane in shallower water than you could if you were operating without the jacking plates. Once on plane, you can adjust or lower the jack plates as appropriate. Jacking plates can be powered via manual or hydraulic means. When powered by hydraulic means there is usually a control panel on the dash which can be used to raise or lower the outboards and also indicates the jacking plate height. Until you are familiar with jacking plates and their use. Utilize the crawl, walk, run method when operating your boat. High speed turns with the jacking plates in the full raised position may result in a loss of control, ejection, or capsizing event.

There are 2 main advantages to using jacking plates:

(01) Operate in shallower water than normal, (02) Increased Efficiency.

Trimming up your outboard(s) causes the bow to go up and the stern down, increasing your draft. However, jacking the outboards up to the point just before cavitation allows for thrust to be directed directly astern and reduces the increase in draft. This is because once water clears the transom; it flows upward into the propeller and provides sufficient water for the propeller(s) to work. Because the thrust is more efficient, not thrusting up or down by using the engine tilt, it helps to save more fuel.

High speed maneuvers can be more difficult when the jacking plates are fully raised. Additionally, a false sense of bravado may occur when determining operational draft realities. Always use sound risk management principles when operating in shallow water. Usually when getting a plane, boats squat in the stern causing the bow to rise and reducing visibility. When trim tabs are used, they increase visibility by reducing the squatting at the stern and in turn lessening the “bow rise” associated with coming up on a plane. Additionally, the engines do not have to work as hard to get on plane and therefore increased fuel efficiency. The tabs are more effective than engine tilt at controlling the pitch axis when already on a plane where the tabs can be manipulated to keep the bow from digging into waves or prevent launching the boat over waves.

motors. As through-hub exhaust gas bubbles are drawn forward into the propeller blade arc, the aerated water increases the possibility of cavitation. Though outboards and stern-drives are fitted with an anti-cavitation plate above the propeller, the coxswain should always take care to limit cavitation, particularly when backing or maneuvering using large amounts of throttle.

A waterjet (Figure 6-14) is an engine-driven impeller mounted in a housing. The impeller draws water in and forces it out through a nozzle. The suction (intake) side of the waterjet is forward of the nozzle, usually mounted at the deepest draft near the after sections of the hull. The discharge nozzle is mounted low in the hull, exiting through the transom. The cross-sectional area of the inlet is much larger than that of the nozzle. The volume of water entering the inlet is the same as being discharged through the nozzle, so the water flow is much stronger at the nozzle than at the intake. This pump-drive system is strictly a directed-thrust drive arrangement. A waterjet normally has no appendages, nor does it extend below the bottom of the vessel hull, allowing for operation in very shallow water.

[Lettered on the illustration: Bucket Impeller Housing Suction Discharge Intake Steering Nozzle]

[Illustration in the handbook: Figure 6-14 — Waterjet]

Vessel control is through the nozzle-directed thrust (Figure 6-15). To attain forward motion, the thrust exits directly astern. For turning, the nozzle pivots (as a stern drive) to provide a transverse thrust component that moves the stern. For astern motion, a bucket-like deflector drops down behind the nozzle and directs the thrust forward. Some waterjet applications include trim control as with a stern drive or outboard. With this, thrust can be directed slightly upward or downward to offset vessel loading or improve ride.

[Illustration in the handbook: Figure 6-15 — Thrust and Directional Control]

Since the waterjet impeller is fully enclosed in the pump-drive housing, no propeller side force is generated. The only way to move the stern to port or starboard is by using the directed thrust.

degree of cavitation normally occurs than associated with external propellers without a loss of effective thrust. In fact, a telltale indicator of waterjet propulsion is a pronounced aerated, water discharge frequently seen as a rooster tail astern of such craft. As the impeller rotation does not change with thrust direction, frequent shifting from ahead to astern motion does not induce cavitation. However, as the thrust to make astern motion reaches the waterjet inlet, the aerated water is drawn into the jet, causing some reduction of effective thrust. As with all types of propulsion, slowing the impeller until clear of the aerated water reduces cavitation effects.

When stepping up to the controls of any vessel for the first time, the coxswain should immediately become familiar with any physical constraints or limitations of the helm and engine controls. Ideally, controls should be designed and mounted to allow for a wide range of operators of different arm length and hand size, though this is not always so.

The coxswain should determine if anything obstructs hand or arm movement for helm and throttle control. Checks should be made for the following obstructions and hazards:

(01) A firm grasp of the wheel through 360°, (02) Anything that prevents use of the spokes, (03) Awkward position of throttle/gear selector, (04) Layout that prevents use of heavy gloves, (05) Inaccessible engine shutdown handles, (06) An easily fouled outboard kill-switch lanyard, (07) Other common sense items.

The coxswain should also learn where all the controls are and know their function before snagging a sleeve while maneuvering in close quarters or banging a knee or elbow in choppy seas. Check control operation while moored with engines secured. Some larger vessels require engine

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operation to operate controls, such as engine-assisted hydraulic steering. If so, check throttle controls with engines secured

The following are some items to check when checking engine control action:

NOTE Perform these steps as part of every getting-underway check.

Joysticks are increasingly replacing legacy helm and throttle controls. In most cases boats will be equipped with two joysticks, one acting as a tiller to adjust heading and the other as the throttle with limited directional control for docking maneuvers. On vessels with jet propulsion, moving the throttle joystick forward will command the jet buckets up and the engines will accelerate, dependent on the amount of joystick forward movement, to increase jet flow for forward motion. Moving the joystick aft will command the buckets down and the engines will accelerate, to increase jet flow for astern motion. Moving the tiller joystick port or starboard will cause the boat to move sideways in the same direction. If wind or current are acting on the boat at an angle, the tiller can be moved slightly to the opposite angle to oppose those forces. The following are some guidelines for determining joystick limits:

Smooth, positive operation of helm and engine controls is absolutely necessary for safe boat operations. Do not accept improper control configuration, mismatched equipment, or improper maintenance as a reason for poorly operating controls. Poor control operation causes unsafe boat operations.

After checking all controls while moored with engines secured, the coxswain should recheck their operation with engines running while securely moored. It may not be safe to apply full ahead to astern throttle, however, a note should be made anytime there is a lag between throttle shift and propulsion, from neutral to ahead, neutral to astern, ahead to astern, and astern to ahead. When going from the ahead position to the astern position, and when going from the astern position to the ahead position, pause briefly at the neutral position. When training, an experienced individual should get the vessel underway and into open water before turning control over to anyone not familiar with the particular boat’s operation. Once in open water, control may be turned over to the new coxswain who should recheck helm and engine control operation at clutch speed.

and firmly. If the vessel is single-screw, outboard, or outdrive, propeller side force will tend to move the stern slightly to starboard (see Figure 6-16). The side force should be offset with slight starboard helm. If twin-engine, throttles should be advanced together. The vessel should not yaw in either direction if power is applied evenly. Engine RPMs should be checked so both engines turn at the same speed. Some vessels have a separate indicator to show if engine RPMs match, but also compare tachometer readings.

[Illustration in the handbook: Figure 6-16 — Accelerated Ahead]

NOTE

Do not ram throttles forward when starting up. As the engines try to transfer the excessive power, the stern will squat, raising the bow and decreasing visibility (see Figure 6-17), and propellers or impellers may cavitate.

[Illustration in the handbook: Figure 6-17 — Pronounced Squat on Acceleration]

Small amounts of helm should be used to offset any propeller side force or the effects of winds and seas. Compass course should always be noted and corrected frequently to stay on course. It is important to develop a practiced eye and steer on a geographic point or range such as a point between buoys. Small, early helm corrections should be applied to stay on course, rather than large corrections after becoming well off course. Oversteering, leaving a snake-like path, should be avoided. At low speeds, helm correction will be more frequent and require more rudder than at higher speeds.

For planing or semi-displacement hulls, the boat will gradually gain speed until planing. If fitted with trim control (including trim tabs on inboard boats), slight, bow-down trim may lessen the amount of time needed to get on plane or “on step.”

Running at full speed all of the time should be avoided. This wastes fuel and can cause excessive wear on the boat and crew. Many vessels will not exceed or will only marginally exceed a given speed, regardless of the power applied. At some point, the only effect of applying additional throttle is increased fuel consumption with no speed increase. Finding a speed that offers a comfortable ride as well as allows mission completion is advised.

A margin of power should always be left available for emergencies. The best speed for the vessel should be determined. A good normal operating limit for semi-displacement vessels is usually 80 percent maximum power, allowing the remaining 20 percent for emergency use.

A boat at high speed has a large amount of force. With an untrained operator, this force can be dangerous. The following factors, and those identified in Rule 6 of the Navigation Rules and Regulations Handbook, should be considered to determine safe speed.

(01) High seas: Slow down as winds and seas increase; the boat will handle more easily. Pounding or becoming airborne fatigues the hull and could injure the crew or cause them chronic skeletal problems. If it takes tremendous effort just to hang on, the crew will be fatigued and not able to perform their jobs. Minimize taking spray and water on deck, NOTE

Find the most comfortable, secure location for the entire crew. For many vessels, this means in the immediate vicinity of the helm.

(02) Traffic density: Do not use high speed in high traffic density areas. A safe speed allows response to developing situations and minimizes risk of collision, not only with the nearest approaching vessel, but with others around it, (03) Visibility: If conditions make it difficult to see, slow down. Fog, rain, and snow are obvious limits to visibility, but there are others. Geographic features and obstructions (river bends, piers, bridges and causeways), along with heavy vessel traffic, can limit the view of “the big picture.” Darkness or steering directly into the sun lessens ability to see objects or judge distances. Prevent spray on the windscreen (particularly salt spray or freezing spray) as much as possible and clean it regularly. Spray build-up on the windscreen is particularly hazardous in darkness or in glare, (04) Shoal waters: In shallow water, the bottom has an effect on the movement of the vessel. Slow down in shallow water. In extremely shallow water, the vessel’s stern tends to “squat” and actually moves closer to the bottom.

Being “on plane” will not allow crossing a shoal that would ground the vessel in the displacement mode. At high planing speed, the stern will squat as it gets in shallow water, possibly grounding at a very damaging speed.

In extremely narrow channels, a vessel moving through the water will cause the “wedge” of water between the bow and the nearer bank to build up higher than on the other side. This bank cushion tends to push the bow away from the edge of the channel. As the stern moves along, screw suction and the movement of water to “fill- in” where the boat was creates bank suction. This causes the stern to move towards the bank. The combined effect of momentary bank cushion and bank suction may cause a sudden shear toward the opposite bank. Bank cushion and bank suction are strongest when the bank of a channel is steep. They are weakest when the edge of the channel shoals gradually and extends in a large shallow area. When possible, a trainee should stay exactly in the center of an extremely narrow channel to avoid these forces (see Figure 6-18). Slower speed also reduces the amount of cushion and suction. Some rudder offset towards the closer bank will help to avoid continuous cushion and suction effects by. Do not overcompensate for bank cushion and bank suction. Too much helm in the direction of the bank

CAUTION !

could cause the bow to veer into the bank. Then, a subsequent large helm movement to turn the bow away from the bank may cause the stern to swing into the bank.

[Illustration in the handbook: Figure 6-18 — Bank Cushion and Bank Suction]

When meeting another vessel close aboard, bow cushion and stern suction occur between the vessels much the same as bank cushion and suction. Helm corrections should be used to compensate. As both vessels move through the water, the combined effect is greater than what a single vessel encounters from bank interaction. Caution should be used so the bow does not veer too far from the intended track and the stern swings into the path of the other vessel. A port-to-port meeting situation is assumed. Before vessels are bow-to-bow, a small amount of right rudder should be used to ensure the bow is clear. The bow cushion will increase separation. As the vessels near bow-to-beam, using left rudder will enable the vessel to keep away from the right-hand bank and to stay parallel to the channel. When the vessels are bow-to-quarter, the bow cushion will be offset by the stern suction, and bank cushion may need to be offset by some right rudder. Finally, as the vessels are quarter-to-quarter, stern suction will predominate, and will require left rudder to keep the sterns apart. The following bow cushion and stern suction considerations apply when meeting another vessel in a narrow channel and when operating near a bank: (01) The deeper the vessel’s draft, the greater the cushion and suction effect, particularly if draft

approaches water depth, NOTE

(02) The closer to a bank or another vessel, the greater the cushion and suction, (03) In very narrow waterways, slow down to decrease cushion and suction effects, but not to the

point of losing adequate steerage.

When meeting another vessel in a narrow channel, the bow cushion and stern suction effects caused by the other vessel should be balanced with the bank cushion and suction effects due to the channel.

As a vessel proceeds, a combination of bow and stern waves move outward at an angle to the vessel track. The wake height and speed depend on vessel speed and hull type. Relatively large, semi-displacement hulls, proceeding at cruising speed, cause some of the largest wakes. Some lighter craft actually make less wake at top speed in the planing mode rather than at a slower speed. Displacement craft make the largest wake at hull speed. The coxswain should determine how to make the vessel leave the least wake; it might require slowing appreciably. All vessels are responsible for their wake and any injury or damage it might cause. Only an unaware coxswain trails a large wake through a mooring area or shallows, tossing vessels and straining moorings. A large, unnecessary wake, particularly in enclosed waters or near other smaller vessels, ruins the credibility of a professional image. While maneuvering, keep the crew informed of “Coming-up,” turning, or “Coming down,” slowing down. A quick warning shout could prevent injury.

To move in a straight line, small, frequent, momentary helm or tiller inputs adjust the position of the stern and bow to head in the desired direction. To intentionally change the vessel heading, larger, more sustained helm movement should be used.

in the opposite direction. As the stern swings a certain angle, the bow swings the same angle. Depending on the fore and aft position of the pivot point, the stern could swing through a larger distance than the bow, at the same angle. When a hull moves forward through the water, the effective pivot point moves forward. The higher the forward speed, the farther the pivot point moves forward.

Because outboards, stern drives, and waterjets use propulsion thrust for directional control, they can make a much tighter turn (using helm alone) with a given hull shape than if the same hull had shaft, propeller, and rudder. With extended outboard mounting brackets, the directed, lower-unit thrust is farthest aft of the pivot point compared to the other configurations. Some brackets move the thrust three to four feet aft of the hull. The location aft of the pivot point, along with the amount of directed thrust determines how much the stern will kick away from the direction of the turn. With directed thrust, the stern will usually skid outward more than with shaft, propeller and rudder, making the bow describe a very tight arc (see Figure 6-19).

[Illustration in the handbook: Figure 6-19 — Pivot Point, Skid, Kick, Inboard vs. Outboard]

When proceeding on a steady heading, putting the helm or tiller over to one side or the other, begins to turn the boat. Up to the time the boat turns through 90°, the boat has continued to advance in the original direction. By the time the boat has turned through 90°, it is well off to the side of the original track. This distance is transfer. As the boat continues through 180°, its path has defined its tactical diameter. If the vessel holds the turn through 360°, the distance it takes to reach the point where it first put the helm or tiller is referred to as its final diameter. For a particular vessel, these values vary for speed and rudder angle (see Figure 6-20). Developing a working knowledge of the vessel’s turning characteristics will enable decision-making such as whether to make a particular maneuver in a certain space solely with the helm or whether other maneuvering tactics are needed. Learning when to ease the helm will help to prevent oversteering a course.

[Illustration in the handbook: Figure 6-20 — Turning Characteristics]

Some planing hulls and most semi-displacement craft will slow appreciably when turning at high speeds. As the boat heels into a turn, the hull provides less buoyancy to keep the vessel on plane at a given speed. Also, as the aft part of the hull skids across the water while in a heel, it presents a flat shape in the original direction of movement and pushes water outward, thus causing the vessel to slow down. With light-displacement, high-powered craft, maximum helm at high speed will quickly stop a boat’s progress in the original direction of movement. Though such a turning action is effective to avoid contact with an immediate hazard, the violent motion could eject unsuspecting crewmembers. Use this technique only as an emergency maneuver. Do not use this maneuver to demonstrate the boat’s capability.

Bank suction, bank cushion (see B.11. Bank Cushion and Bank Suction above), and currents will all affect a boat navigating a sharp bend in a narrow channel. Where natural waterways have bends or turns, the water is always deepest and the current is always strongest on the outside of the bend. This is true for 15° jogs in a tidal estuary and for the “s” shaped meanders on the Mississippi River. This happens because the water flow has a great degree of momentum and resists having its direction changed. As it strikes the outside of the bank, it erodes the earth and carries the particles with it. The particles fall out farther downstream in areas of less current (the inside of a turn or bend) and cause shoaling. In some turns or bends, there may be circular currents (eddies) in either the deep outside of the bend or the shallow inside. Back currents also sometimes occur near eddies on the inside of the bend. When eddies or back currents occur, those near the shallows are much weaker than eddies or main current flow at the outside of the bend. Because bank cushion and suction are strongest when the bank of a channel is steep and weakest when the edge of the channel shoals gradually, bank effect is stronger on the outside of bends or turns. The coxswain should be aware of the mix of current and bank effect and use these forces to the fullest extent.

The effect of a head current is minimized by steering along the inside quarter of the channel, making sure to avoid shoaling. If the bow gets into the area of greater current, it may begin to sheer towards the outside of the bend. It can be countered through helm towards the inside of the bend and by getting the stern directly down current from the bow. The vessel can then be gradually worked back to the inside quarter of the channel. If the starting point is the outside of the bend, the full force of the current will be encountered. Bank cushion should keep the bow from the outside edge, but the stern is limited in its movement by bank suction. Initial helm towards the inside of the turn may allow the current to cause the bow to rapidly sheer away from the outside, but this is immediately offset with power and helm to keep the bow pointed upstream. Gradual helm with constant power should be used to get out of the main force of the current, and work across to the inside quarter of the channel.

The turn on a course should be approached just to the outside of the middle of the channel. This will avoid the strongest currents at the outside edge while still getting a reasonable push. While turning, the strongest current will accentuate the swing of the stern quarter to the outside of the channel. Because of this, and because the following current tends to carry the boat toward the outside, the turn should begin early in the bend. The amount of sideways movement or if the boat tends to “crab” in the channel should be constantly monitored. If the boat starts to move too close to the outside of a bend, more helm and power should be constantly monitored to maneuver the boat back into the middle. Once through the turn, the vessel can be gradually worked back to the inside quarter of the channel.

(01) If the boat stays too far to the outside of the bend, timing the turn is difficult. Turning too early with stern suction on one quarter with the strongest current on the other quarter may cause an extreme veer to the inside of the turn. Any bow cushion will accentuate the sheer. Turning too late with stern suction and the quartering current could cause grounding. (02) If trying to hug the inside of the turn, both current and bank effect will be lessened. Use a small amount of rudder toward the inside bank to enter the turn. As the channel begins to bend, use less rudder while the boat starts to move from the inside bank. Use caution as the current under the quarter affects the stern, giving it an increase in sheer towards the inside bank. Slack water or an eddy down current on the inside will increase this sheer while bow cushion may not be enough to prevent grounding.

Pulling back the throttle to neutral will cause the vessel to begin to lose forward motion. For a heavy-displacement vessel, once propulsion is stopped, the vessel will continue to move forward for some distance. The vessel carries its momentum without propulsion. For a semi-displacement hull or planing hull, reducing power will cause the boat to quickly come off plane. As the vessel reverts to displacement mode, the resistance of the hull going through the water instead of on top of the water slows the boat. The vessel still carries some way, but at only a fraction of the original speed. The coxswain should experiment with the vessel and see how rapidly the boat slows after going from cruising speed to neutral throttle. Knowing the distance the vessel will travel when stopping (also known as head reach) from different speeds is very important when maneuvering.

Slowing the vessel’s forward movement is not always enough. In an emergency situation, a complete and quick stop to dead-in-the-water or crash stop may be required. This is done by applying astern propulsion while still making forward way. The first step is to slow the vessel by placing the throttles in the clutch astern position. After the vessel begins to lose way, astern propulsion should be applied firmly and forcefully. Power must be higher than that available at clutch speed to prevent engine stall. On a single- screw vessel, the stern will want to swing to port. After all way is off, the throttle should be placed in neutral. At low forward speeds, astern propulsion is frequently used to maneuver, both to check forward way and to gain sternway. Though many vessels are tested and capable of immediately going from full speed ahead to full reverse throttle, this crash stop technique is extremely harsh on the drive train and may cause engine stall. Though much of the power goes to propeller cavitation, this technique can be effective in an emergency. With a waterjet, reverse thrust is immediate. There is no marine gear or drive unit that requires the shaft and propeller to change rotation directions. The clamshell or bucket-shaped deflector plate drops down and redirects thrust forward. The crash stop is an emergency maneuver. It may damage the drive train and stall the engine(s). In most cases, with high levels of crew professionalism, skill, and situational awareness, it is not necessary.

When stopping vessels with outboard engines making forward way, the coxswain should follow the below procedures.

The crash stop is an emergency maneuver or an advanced tactical technique. It may damage the lower unit or stall the engine(s) if performed incorrectly. If engines are stalled place throttles into the neutral position and restart the engine(s). It is important to

NOTE

remember that some platforms may require the operator to return the key switch(s) to the off position before allowing the engines to restart.

As noted above, with light-displacement, high-powered craft, maximum helm at high speed will quickly stop a boat’s progress in the original direction of movement. To fully stop, the throttle should be placed down to neutral after entering the skid. If done properly, no astern propulsion is required. With a jet drive, no directional control will be available without thrust. The boat must be in a skid

NOTE

before reducing power. If thrust is reduced before trying to turn, the boat will slow on the original heading. Do not back in a way that allows water to ship over the transom. Be careful with boats of very low freeboard aft. Outboard powered vessels, with low cut-out for motor mounting and a large portion of weight aft are susceptible to shipping water while backing, particularly in a chop. If shipped water does not immediately drain, it jeopardizes stability. Most inboard engines exhaust through the transom. Outboard motors exhaust astern. Backing could subject the crew and cabin spaces to a large amount of exhaust fumes. Limit exposure to exhaust fumes. If training, frequently change vessel aspect to the wind to clear fumes. After backing, ventilate interior spaces.

Control while making sternway is essential. Because vessels are designed to go forward, many vessels do not easily back in a straight line. Due to higher freeboard and superstructure forward (increased sail area), many vessels back into the wind. Knowledge of how environmental forces affect a boat is critical when backing. Besides watching where the stern goes, the coxswain should keep track of the bow. The stern will move one direction and the bow the other direction around the pivot point. As a vessel develops sternway, the apparent pivot point moves aft and the bow may swing through a greater distance. Firm control of the helm should be maintained to prevent the rudder or drive from swinging to a hard-over angle.

While backing, the rudders have less water flowing over them, due to the propeller being directly forward of the rudders, therefore there is less directional control of the boat. Because steering control comes from water flow across the rudder, the more sternway the vessel has, the greater water flow across the rudder leads to more control.

Propeller side force presents a major obstacle to backing in the direction desired. The rudder does not have much effect until sternway occurs, and even then, many boats will back into the wind despite a best effort to do otherwise. If backing to the wind, the coxswain should know at what wind speed the boat will back into the wind without backing to port.

(01) Before starting to back, apply right full rudder to get any advantage available. (02) A quick burst of power astern will cause the stern to swing to port, but use it to get the boat moving. (03) Once moving, reduce power somewhat to reduce propeller side force and steer with the rudder. As sternway increases, less rudder will be needed to maintain a straight track astern. (04) If more sternway is needed to improve steerage, increase power gradually. A strong burst astern will quickly swing the stern to port. (05) If stern swing to port cannot be controlled by the rudder alone, use a burst of power ahead for propeller side force to swing the stern to starboard. Do not apply so much power as to stop sternway or to set up a propeller discharge current that would cause the stern to swing farther to port. (As the vessel backs, it uses sternway water flow across the rudder to steer). (06) If this fails, use a larger burst of power ahead, with helm to port. Sternway will probably stop, but propeller side force and discharge current across the shifted rudder will move the stern to starboard. Now try backing, again.

Both engines should be backed evenly to offset propeller side force. Using asymmetric power (one engine at higher RPM than the other) will help steer the stern. Asymmetric power will also give unequal propeller side force that will help steer.

(01) Apply astern power evenly, keeping rudders amidships. (02) If the stern tends to one side, first try to control direction with slight helm adjustment. If not effective, either increase backing power on the side toward the direction of veer or decrease power on the opposite side.

The coxswain shall use the directed thrust to pull the stern to one side or the other. As the power is applied aft of the transom he/she should, use care to keep the bow from falling off course due to winds, avoiding cavitation that can easily occur when backing with a lower unit. Propeller side force is present, but is offset through helm. A lower unit that is not providing thrust is not efficient when trying to steer while backing. It is better to keep steady, slow RPMs than to vary between high power and neutral.

For single-outboard/outdrive, propeller side force is offset by turning the helm slightly to the right. Astern power is then applied gradually, but care should be taken not to cause propeller cavitation.

If astern power is matched, propeller side forces will cancel. As with twin inboards, offsetting any stern swing with helm should be attempted before using asymmetric power. If less thrust than that provided by both drives at clutch speed is needed, one motor or engine should be used. This will keep speed low but will keep thrust available for steering, rather than shifting one or both engines from reverse to neutral. If using one unit, compensate with helm for propeller side force and the increased, off-centered drag caused by the other lower unit.

Waterjets draw water in through an inlet grate in the hull, accelerated by means of an impeller, and thrust it out the transom in a small, high-velocity stream through a steerable nozzle. This nozzle is fitted with a reversing bucket, the deflector that drops down and deflects water forward to stop or reverse the boat. There is no propeller side force and thrust is directed as with an outboard. Going from forward to reverse thrust has no marine gear or drive train to slow things. Thrust is simply redirected with the “bucket.” Unless thrust is applied and being directed, there is no directional control at all. The power must be on and applied to steer either forward or in reverse. Bursts of power astern when backing should be avoided. Bursts of power when making astern thrust will excessively aerate the waterjet intake flow ahead of the transom.

Asymmetric propulsion while backing was covered in previous paragraphs. The techniques presented here are additional methods of maneuvering that capitalize on twin-engine vessel capability to differ the amount or direction of thrust produced by the two engines. Any difference in thrust affects the boat’s heading. The amount of this difference can vary from that needed to hold a course at cruising speed to turning a boat 360° in its own length by opposing propulsion (splitting throttles). The concept of asymmetric or opposed propulsion can be likened to “twisting” the boat, but the forces and fundamentals discussed earlier still apply and affect vessel response. Pivot point, propeller side force, and turning characteristics remain important. Because the drives are offset from vessel centerline on a twin-engine vessel, they apply a turning moment to the hull. Twin outboard motors on a bracket apply this twist aft of the hull (and well aft of the hull pivot point), while twin inboards apply most of this twist to the hull at the first thrust-bearing member of the drive train (usually the reduction gear or v-drive, much closer to the pivot point). With inboards, propeller side force is transferred through a strut and stern tube to the hull. Up to a point, the greater the difference in RPMs, the greater the effect on the change in heading. Above that point, specific for each boat, type of propulsion, sea conditions and operating speed, cavitation or aeration will occur, and propulsion efficiency will decrease, at least on one drive.

NOTE

As with all boat handling techniques, learn these first in calm weather, in open water, and at low speeds.

Depending on a vessel’s topside profile, wind conditions might make the bow continually fall off to leeward. Though the helmsman can compensate for this by steering with constant pressure to hold desired course, a less taxing way is to adjust the throttles so the leeward engine turns at more RPMs than the windward engine. The difference in RPMs can be fine-tuned until pressure is off the helm.

The following techniques cause a faster change in heading by increasing both skid and kick, reducing advance and transfer, and if the heading change is held long enough, the overall tactical diameter.

Rotating about the pivot point is a low-speed maneuver. It is important because situations will occur when the boat’s heading needs to be changed (to the weather or another vessel) or the bow or stern moved in a limited area. The engines should be opposed to turn in an extremely tight space. This maneuver is first performed at clutch speed in calm conditions to learn how the vessel reacts and what type of arcs the bow and stern describe. With no way on, there is no initial advance and transfer, so depending on the boat; this maneuver might yield a tactical diameter of zero if the heading is changed 360° (rotating the vessel in its own length). The forces involved should be considered. Vessels with propellers will develop side force from both drives during this maneuver. The rudder, where equipped, can use propeller discharge current from the ahead engine to help pivot the stern. Because boats operate more efficiently ahead, some headway may develop.

With helm amidships, perform the following procedures:

Put the helm or tiller over hard-to-port by performing the following procedures:

All crewmembers must pay close attention to throttle changes and vessel movements. Firmly hold onto the vessel during these maneuvers.

With the basic skill in hand, practice controlling the amount of swing by performing the following procedures:

Experiment with the vessel.

Though turning should help increase the rate of swing, the increase in turn rate might not be worth the workload increase (stop-to-stop helm/tiller use). Due to swing rate, full helm/tiller use NOTE may not be as effective as leaving the helm centered. At some level of power for each vessel and drive train arrangement, cavitation will occur with split throttles. Know at what throttle settings cavitation occurs. More power will not increase turning ability and might cause temporary loss of maneuverability until cavitation subsides. In critical situations, loss of effective power could leave a vessel vulnerable.

An emergency maneuver at cruising speed may require a turn with reduced tactical diameter.

An effective technique for a twin-propeller boat is to have one propeller act as a brake. This creates drag on the side with that propeller and reduces the turning diameter.

Do not put throttle to neutral position. In neutral, the propeller will “free-wheel” and rotate without

NOTE

any resistance. Keeping the engine in clutch ahead will keep the propeller from spinning freely and start “braking” the vessel on the inboard side.

This practice is also more effective with shaft, propeller, and rudder arrangement than with directed thrust drives. One propeller will still be providing forward thrust while the other will be backing. As with opposing thrust in low speed maneuvering, propeller side force is multiplied. Cavitation will be pronounced on the backing propeller, but the vessel’s forward motion keeps advancing this propeller into relatively undisturbed (or non-aerated) water.

As with the crash stop, this maneuver is extremely hard on the engine and drive train. The backing engine’s power must be higher than that available at clutch speed to prevent engine stall.

Basic maneuvering techniques should be applied in combination with a single propeller at low speed to further boat handling skills. Practice these maneuvers in calm, no-current situations before learning to overcome environmental forces. A single-screw vessel never has the ability to use asymmetric or opposed propulsion, and its coxswain must develop boat handling skills with this in mind. The operator of a twin-engine vessel could easily become limited to use of one drive due to engine failure or fouling a propeller, and must also become a proficient, single-screw boat handler. For the discussion here, the case of a single-engine propeller vessel with right- hand turning propeller is used. When maneuvering a twin-engine vessel on one drive, the coxswain must account for the propeller rotation and side force for the particular drive used (normally starboard: right-hand turning, port: left- hand turning), and the offset of the drive from centerline.

The back and fill technique, also known as casting, provides a method to turn any vessel in little more than its own length. At some point, anyone who operates a single-screw vessel will need to rely on these concepts when they operate a boat, particularly in close-quarters maneuvering. To back and fill, the coxswain should rely on the tendency of a vessel to back to port, and then use the rudder to direct thrust when powering ahead to starboard. The coxswain should also decide the radius of the circle in which to keep the vessel (at most, 25 to 35 percent larger than the vessel’s overall length), and the intended change in direction (usually no more than 180°) before starting. For initial training, the vessel should be turned through at least 360°. From dead-in-the-water position, perform the following procedures to back and fill:

(01) A firm grasp of the vessel’s maneuvering characteristics is necessary to know whether to back

and fill rather than just maneuver at full rudder.

(02) The amount of steps used will depend on size of the turning area and the desired change in

heading. The smaller the area, the more backing and filling required.

(03) Winds will play a factor in casting. If the vessel’s bow is easily blown off course, the vessel

NOTE probably has a tendency to back into the wind. Set up the maneuver (including direction of turn) to take advantage of this in getting the bow to change direction. Strong winds will offset both propeller side force and any rudder effect.

(04) A quick helm hand is a prerequisite for casting with an outboard or stern drive. To get full

advantage of the lower unit’s directed thrust, fully shift the helm before applying propulsion.

(05) With helm at left full, the propeller side force when backing will have an element that tries to

move the stern “forward” around the pivot point.

When operating a duel waterjet platform both waterjets work in tandem unless placed in docking mode. The pictures below show only one waterjets. The reader should be conscious that the second waterjet is performing the same functions simultaneously of the waterjet pictured.

Ahead

Zero Thrust

Coxswains must learn to manage the effects of environmental forces by using power and helm to maintain their position next to an object. Station keeping is defined as maintaining distance, position and aspect to or from an object. With twin propulsion, coxswains need to develop the skills required to maintain any aspect to an object during most conditions. Though many single- drive boats are thought to be less maneuverable, coxswains should fully develop single-drive station keeping skills should the need arise. Station keeping should be practiced during various levels of wind, seas, and current.

NOTE

All coxswains of twin-drive vessels must frequently train for single-drive operation. This includes station keeping.

Each situation requires a safe maneuvering zone to reach an optimum position near the object so an evolution can safely occur and can be done effectively (e.g., equipment transfer, object recovery, surveillance, etc.). Staying in the maneuvering zone keeps you out of the danger zone and gives you a way out if you encounter problems while station keeping. Before station keeping perform the following procedures to determine a safe and effective maneuvering zone: When station keeping, always have a safe escape route to get clear of the object or any hazard. While station keeping, ensure the escape route stays clear. This may require changing position to establish a new escape route.

The coxswain should station keep close enough to complete a mission or evolution, yet far enough to prevent collision or allision. Minimum safe distance to the object will probably vary around the object or along its length. Environmental conditions and boat maneuverability play a major role in determining distance. The coxswain should perform the following procedures:

Station keeping will usually require frequent to near-continuous applications of power and helm to stay in the safe maneuvering zone. While station keeping and trying to stay within the maneuvering zone limits, adjusting for one of the parameters (distance, position, aspect) will almost always involve a change to one or both of the other two. While using power and helm to compensate for and to overcome wind and current, the wind and current should be used to the fullest extent.

To stem the forces means to keep the current or wind directly on the bow or stern and hold position by setting boat speed to equally oppose the speed of drift.

To crab the boat sideways, environmental forces should be used to move the boat at a right angle to the forces. The coxswain should put the bow at a shallow angle (20° to 30°) to the prevailing force and use propulsion and helm to keep from getting set backward, while staying at the shallow angle to the prevailing environmental force.

Make a vessel “open” and “close” the distance on the object at various angles, both to leeward and to weather. With an object on the bow or stern, directly up-drift or down-drift from you, opening and closing requires only to compensate for the fore and aft drift rate and to maintain a steady heading. A combination of control and environmental forces should be used:

(01) Side force, (02) Ahead and astern thrust, (03) Rudder force, (04) Leeway, (05) Current, (06) Drift.

The more difficult scenario is opening or closing distance abeam.

Differences in objects determine the maneuvering situation. Coxswains should become fully capable of station keeping in a variety of situations with both different types of objects and environmental conditions.

Object type and size ranges from small items floating in the water to other vessels. No two items will drift at the same speed through the water. Free- drifting objects will present a different drift rate from the vessel. The coxswain should develop station keeping techniques by first comparing your drift rate to the object, and then overcoming the difference. The following are procedures for station keeping on a free-drifting object:

Station keeping on an anchored object limits much of the object’s movement due to wind and current, but the object will often surge and swing. A vessel will react freely to the wind and current. The object will ride with its moored end into the strongest environmental force affecting it, while the combination of forces on a vessel may cause it to take a different aspect. Station keeping on an anchored object helps determine where to and where not to maneuver. The following are procedures for station keeping on an anchored object:

When determining approach, the following conditions should be considered:

(01) Prevailing weather, (02) Currents, (03) Location, (04) Vessel conditions, (05) Vessel sizes, (06) Traffic density.

The coxswain should discuss intentions with the other vessel’s master. Do not approach from leeward if it will put the vessel and crew in jeopardy, whether from shoal water or obstructions farther to leeward, or from smoke or hazardous fumes. If going alongside a disabled vessel or one that is underway but dead-in-the water, compare relative drift rates. When approaching a larger vessel with a low drift rate, approach from leeward. If

NOTE

approaching a smaller vessel, determine if vessel makes a wind shadow that will slow the other vessel’s drift. In this case, an approach from windward may be better, and the smaller vessel will then be protected from winds and waves by the larger vessel. See Reference (b) for more information.

If possible and prudent, the vessel should maintain a course and speed to make the approach as smooth as possible for both vessels.

Most large vessels will not be able to alter course significantly in a limited area to provide ideal alongside conditions. If it is not practical for the large vessel to change course, the coxswain should request that it reduce speed so the effects of bow and stern waves are reduced.

Small vessels do not ride well when not making way in any kind of winds or seas. Unless the weather is perfectly calm or the vessel is disabled, a small vessel should maintain a course and speed that makes for safe, comfortable navigation while allowing mission completion. Speed should be slow enough to safely come alongside, but fast enough for both vessels to maintain steerageway when alongside one another.

Many sailing vessels are much more stable while under sail than when powering or drifting. The coxswain should consider coming alongside while the other vessel is under sail, but should ensure that spars, standing or running rigging, or control lines do not foul either vessel. The situation should be discussed with the other vessel’s master. Make sure the other vessel does not change course while approaching or coming alongside. If this happens, break off and start the approach over again once the other vessel is on a steady course. Inform the master to maintain course and speed until the transfer is complete.

A large vessel will create a wind shadow and block most of the seas allowing a smoother approach on the leeward side of a vessel. Coxswains should take advantage of this as in mooring to the leeward side of a pier. When approaching smaller vessels, the coxswain should first determine the smaller vessel’s rate of drift. The coxswain can then determine if an approach on the leeward side (better control over approach) or windward side (a wind shadow will be created) would be better. If an approach from leeward is not possible (due to sea room or other condition like smoke or

NOTE

hazardous vapors), use caution during a windward approach to prevent being pinned up against the side of another vessel. If approaching on the windward side is a must, a bow-in approach might provide the most maneuverability.

Lines and fenders should be rigged as needed. Remember that with fenders, too many is much better than too few.

After completing approach preparations, the coxswain should go alongside and determine where to make contact on both vessels. Perform the following procedures to close in on another vessel:

If initial heading was parallel to the other vessel, increase speed slightly when starting to close at an angle.

NOTE

Pick a contact point well clear of a larger vessel’s propeller (including in the area of suction screw current), rudder, and quarter wave. Forces from these could cause loss of control.

In some instances, a sea painter may be used in coming alongside a larger vessel underway. The sea painter is a line used to sheer a boat clear of a ship’s side when underway or to hold a boat in position under shipboard hoisting davits and occasionally to hold the boat alongside a ship in order to embark or disembark personnel. It leads from the larger vessel’s deck well forward of where the boat will come alongside. Perform the following procedures when securing a sea painter to the boat:

As both the boat and ship have headway, the pressure of water on the boat’s bow will cause it to sheer away from the ship. The coxswain should use this force by a touch of the helm to control sheer, in or out or, by catching the current on one side of the bow or the other. Riding a sea painter helps maintain position and control of the boat.

NOTE

When sheering in or out, apply rudder slowly and be prepared to counteract the tendency of the boat to close or open quickly. Perform the following procedures if using a sea painter:

If approaching a vessel anchored in a strong current, the sea painter can be used to provide a means to

NOTE

lie alongside. Procedures are the same as if the vessel is making way. Approach from leeward, against the current.

Perform the following procedures to make and hold contact with a vessel:

When alongside and conducting the intended missions, the coxswain should:

Getting set toward the side or stern of the vessel should be avoided. Perform the following procedures to clear the side of a vessel:

CAUTION !

Never back down when clearing alongside. Always pull away parallel to the other vessel that is making way. If on a sea painter, use enough speed to get slack in the line, then cast off once clear. Ensure the sea painter is hauled back aboard the larger vessel immediately to prevent it from catching in the screws.

NOTE

If operating a twin-screw boat, go ahead slowly on the inboard engine. This also helps to keep the boat clear of the ship’s side.

In heavy weather, the motion of the boat rolling, pitching, and yawing affect handling of the boat. If these motions become excessive or combine, they may become uncomfortable or even dangerous. High winds affect boat handling and may amplify control problems.

Rolling occurs when the boat is running beam to the seas. If the course requires running or turning broadside to heavy seas, the boat will roll heavily, possibly dangerously. In these conditions, it may be best to run in a series of tacks like a sailboat, changing course to take the wind and seas at a 45° angle. Sea breaks can exert considerable pressure on the side of the boat, which is resisted by the water on the lee side. This can produce a turning moment which if greater than the initial righting moment will result in a knockdown or rollover. To turn sharply while exposing the boat to a beam sea for the least amount of time, the coxswain should slow down for a few seconds, then turn the helm hard over and apply power. This can be done effectively with a twin-screw boat by using the split-throttle maneuver or in the case of jet drive boat, turn the tiller hard over and drop the bucket until the boat is square with the wave.

Pitching occurs when the boat is running bow into the waves. The bow of the boat rises over the wave and then drops rapidly into the trough. If the seas become too steep, speed should be decreased. This will allow the bow to rise, meeting the swell, instead of being driven hard into it. Changing course may be the better option to reduce stress on the crew and boat. Again, 45° off the swell may give better control and a better ride. If conditions become too hazardous, slow until the boat is making bare steerageway and meets the seas on the bow. Again, power should be used to negotiate the wave without sending the boat launching off the back of the seas.

Yawing occurs when the boat is operating in following seas. The boat sheers off to port or starboard due to the action of the waves. The boat surfs down the face of the wave, slowing as the bow digs into the trough. The rudder loses control and the sea takes charge of the stern. At this stage, the boat may yaw so badly as to broach (to be thrown broadside out of control) into the trough. Once the wave clears the stern, it lifts the bow of the boat and the stern begins to slide down the backside of the wave, allowing better rudder control causing the boat to straighten out. Jet drive boats have no rudders and little protruding below the hull. This allows for excellent sea-keeping ability when running stern to the seas. As with propellers, adjust speed to maintain position on the back of the wave. Severe yawing may result in a knockdown, pitch pole, or rollover. Extreme care must be taken when operating in a large following sea, constantly watching behind the boat. Slowing speed or changing course may reduce yawing.

High winds can amplify conditions discussed in the previous sections. It can make routine operations such as towing approaches extremely difficult. Overcoming the affect of wind requires practice and experience on the boat.

Awareness of the position of your throttles at all times is of paramount importance when operating in heavy weather. All throttle inputs should be timely and deliberate. Every effort to familiarize yourself with the operation of the throttles should be made. A lack of throttle awareness will prove to be a severe hindrance when attempting complex maneuvers, especially in a heavy weather environment.

Coxswains/operators should always keep one hand constantly on the throttle control(s) to manage their engine propulsion.

Use the following procedures when managing the power of heavier vessels:

Use the following procedures when managing the power of lighter vessels:

“Flying through” the crest should be avoided at all costs. If a large vessel becomes airborne at the top of a wave, the crew is threatened with serious injury and could damage the vessel when it lands. With lighter craft, ensure the after sections stay in contact with the water, but do not let the bow sections get too high. If the bow sections get too high while going through a crest, the apparent wind or the break can carry the bow over backward. On the other hand, if forward way is lost with the stern at the crest, the bow might fall downward, requiring to redeveloping speed and bow-up attitude before the next wave approaches.

Station keeping is maintaining a given position in heavy weather. Station keeping is necessary to hold position while waiting for a window or lull, or holding position prior to and during recovery of a PIW. Environmental factors such as the seas, wind or currents can make station keeping difficult. Therefore, good backing skills and proper application of power are essential. The following are guidelines for station keeping:

(01) Use only enough power to maintain position and counteract the force of the oncoming wave. On smaller waves, keeping the bow square with neutral throttles may be all that is needed, while larger waves may require a great deal of power to counteract, (02) If needed while operating the Response Boat – Medium (RB-M), increase the idle by adjusting the knob. This can increase maneuverability and sea keeping power on demand, (03) Using too much power will set the boat out of position and/or launch the boat. Too little power will cause the boat to be set backwards, or broach the boat, (04) Keep the bow as square to the seas as possible, (05) If the boat is being set towards the seas by current or wind, it may be necessary to back down frequently to hold position, only applying forward power to meet oncoming waves. Wait until a wave crest passes and back down once on the backside. Do not back down on the face of a wave, (06) By adjusting power, it may be possible to safely allow a wave to set the boat back to regain position. This technique requires practice, and the operator must maintain control of the maneuver at all times, (07) It is possible to move laterally while station keeping by allowing the bow to fall slightly to the desired side and then using the throttles and helm to straighten out as the wave pushes the bow.

For example, to crab sideways to port, allow the bow to fall slightly to port and as the wave pushes the bow, apply power and steer to starboard, finishing the maneuver with the bow once again square to the seas. This maneuver must not be attempted on large waves, and it is important not to allow the bow to falloff so far that the safety and control of the boat are compromised. Using docking mode in open waters is not recommended. It was designed for close-quarters situations

NOTE

near a dock or berth. Use standard open and close techniques to maintain position in heavy weather. An increase in idle also increases the amount of suction drawn into the waterjets. Crews must be aware

NOTE

of all lines and gear being passed to a disabled vessel to ensure it does not get sucked into the waterjet intakes.

Making fast and effective turns requires knowledge of the boat’s capabilities and skill in handling. A full power, full rudder, 180-degree turn takes over 20 seconds to complete. For this reason, splitting the throttles and pivoting may be your preferred method in certain conditions.

The

technique for performing this split throttle turn is outlined below:

NOTE

In certain situations (i.e. turning 180° but not wanting to stop the boat) this maneuver may be executed without the backing throttle. The steps described in the “split throttle” turn are designed to achieve a faster turning speed while

CAUTION!

reducing the wear and tear on the entire propulsion system. This maneuver should be used only in the most extreme of circumstances.

[Illustration in the handbook: Figure 6-26 — Split Throttle Maneuver]

CAUTION!

Initiating a Heavy Weather (Split Throttle) turn on the face of a steep wave can result in a knockdown/ rollover and should be avoided.

Due to the maneuverability and speed of Heavy weather / Surf platforms it is capable of avoiding waves when running outbound.

Wave avoidance is

preferable no matter what situation you are in. However, if you do not make prudent decisions while driving, such as maneuvering to shoulders and low sides of waves, the lifeboat may be unintentionally launched out of the water. This can cause severe injury to your crew, damage to certain vessel systems and may potentially disable the vessel when the sortie has just begun.

Heavy weather / Surf platforms ride well at full speed in open head seas up to 6'. Head seas over 6' may require that the speed be reduced, as necessary, to soften the ride. Increased sea states may dictate further speed reductions for the benefit of crew safety. Relatively smaller, but steeper seas (steep chop) may require that the speed be reduced in lesser sea states. Large open ocean ground swells typically pose no problem, however, and speeds can be increased and adjusted to accommodate crew comfort. The coxswain must find a safe and comfortable speed, avoid launching the boat and avoid burying the bow in a wave.

Taking larger head seas slightly off of either bow can create a more comfortable ride, as the boat may proceed more gently off the back of the wave instead of slamming violently. The speed and angle of approach will have to be adjusted as needed for the optimum ride. This is sometimes referred to as quartering the seas, which is not to be confused with taking a following sea on the quarter.

An effective method of transiting through head seas while staying in the power-band of the engines and preserving built up momentum is often referred to as the “Turn and Drag” method. This method prevents launching while simultaneously avoiding the high-side of the wave. The procedures of the turn and drag is below:

Whenever possible, you should avoid steering a course parallel (broadside) to heavy swells. Tack across the swells at an angle (30 to 40 degrees). If necessary, steer a zigzag course, making each leg as long as possible, and adjust the boat speed for a safe and comfortable ride. Seas directly off the beam of the boat can cause adverse rolling conditions. When transiting parallel to the seas, the boat will tend to ride the contour of the wave surface. This means that the boat’s vertical axis will remain perpendicular to the surface on which the boat is operated. A wave face of 20 degrees will cause a 20-degree heel.

If you must take up a course which places the boat beam-to the seas, it is vital to remain vigilant against the incoming waves. If at any point you see a swell which can possibly steepen up or even break, you should not hesitate to square up. Putting the bow of the boat into threatening seas is the best way to ensure total control of your vessel and should never be viewed as the “wrong” course of action.

Following open seas can be negotiated at full speed as long as the boat remains stable as it travels down the front of the swell. However, large following seas may require a reduction in speed to maintain stability and avoid injury to the crew.

While running inbound in waves over ten feet, position the boat on the back of a wave and adjust the speed so the boat will ride in on the back of the wave. You must also watch astern to remain aware of if and when you’ll be overtaken by another wave. While riding on the back of a wave in heavy weather, monitor the boat’s speed closely to avoid overtaking the wave as its speed toward shore decreases. On the 47 MLB utilizing a slow turn back and forth (S-Turning) or quickly “Sallying” your rudder full right and full left may help you avoid this occurrence. In some situations (aerated water, face of a wave)

NOTE

reducing the engine RPM is not advised as a means to slow the boat as the propellers can provide needed “screw-suction” in a precarious situation.

While operating the 47FT MLB stern to the seas >6’ and RPMs >1800, the boat is prone to being caught on the hard chine. Being caught on the hard chine is best described as the boat suddenly heeling over 50-80 degrees on a false keel. In short, this condition is caused by the speed of the MLB and its relative angle to the swell.

The coxswain’s corrective action shall be to immediately reduce power to return the boat onto the true keel Due to the uncertain effectiveness of the previous method, many operators have grown to rely upon the following techniques as a means of correcting Hard Chine Lockup:

(01) Quickly reducing (200-300 revs) and increasing the engine R.P.M.’s on the throttle away from the heel of the boat, also known as the “high side” throttle. Care must be exercised to ensure this reduction in shaft RPM is not so extreme or prolonged that it affects the screw suction of the high side propeller, NOTE (02) Turning the helm fully in the direction of the heel and then immediately back to amidships (center). This violent and athletic maneuver has the effect of rocking the MLB off of its false keel while simultaneously helping the boat take up a more square, down-swell heading (removing the angle from the speed and angle equation). This “turn-in, turn-out” method should be vigorously employed until the lockup is corrected.

When transiting harbor entrances, inlets, or river entrances in rough weather, there will be times when the vessel must either leave or enter port in challenging conditions. Though certain locations have extreme conditions much more often than others, learning how rough weather affects the various harbors and entrances throughout the local area is essential. Methods covered above for maneuvering in head, following, and beam seas still apply, but the entrance areas add additional consideration.

Though mentioned above, local knowledge is key. Knowing as much as possible before transiting an entrance in rough weather will help guard against potential problems. Utilize the following procedures and considerations to assess entrances areas:

Transiting when the current opposed the seas presents the most challenging situation near an entrance. In opposition to the seas, a current has the effect of shortening the wavelength, and increasing the wave height. This makes waves much more unstable and much closer together. Utilize the following procedures and considerations to transit when the current opposes the seas:

In a situation of transiting when current and seas coincide, a current has the effect of lengthening the waves. Longer waves are more stable, with the crests farther apart, but caution is still needed. Utilize the following procedures and considerations to transit when current and seas collide:

high winds do not always accompany large swells. Also, there will be instances when extreme winds occur without sufficient duration to make large waves. Much of the time, though, high winds and building seas will coincide.

Depending on the vessel’s sail area, it may be necessary to steadily apply helm or asymmetric propulsion to hold a course in high winds. Coxswains should learn to “read” the water for stronger gusts. The amount of chop on the surface will increase in gusts, and extremely powerful gusts may even blow the tops off waves. The effect of a gust should be anticipated before it hits the vessel. Utilize the following procedures and considerations when crabbing through steady winds:

A knockdown or rollover is never routine, but always possible. These unpleasant events must be considered and planned for. Training and experience will give a crewmember the edge, but it can still happen simply because of the severe environment he or she is operating in. The following risk management practices should be followed:

(01) All crewmembers must be properly outfitted in PPE, (02) All crewmembers should be familiar with the causes of a knockdown, rollover or pitch poling, as well as how to recognize an impending event, and what to expect, (03) All crewmembers should be well-trained in the procedures to be followed for a knockdown, rollover and involuntary beaching. Crewmembers must be familiar with the procedures for emergency anchoring and drogue deployment as well as the location of necessary equipment. Always brief the crew prior to entering a surf zone, (04) Crewmembers should be prepared to take control of the boat should the operator be injured, incapacitated or lost overboard. The crewmember should also have the skills to maneuver the vessel to recover the man overboard, (05) A backup surf capable resource or aircraft should be standing by whenever possible, positioned where it can observe the boat working in the surf, (06) Backup communications (handheld VHF) should be aboard the boat in case the antennas are lost, or the main radio is damaged.

The risks versus the potential benefits should always be assessed. A sense of urgency must not cloud judgment or cause the loss of situational awareness.

The following procedures apply in a knockdown/rollover:

Do not unfasten safety belt or consider swimming to the surface. It is likely the propellers will still be turning, and the boat is designed to right itself in a few seconds. When the boat rights itself it may strike you in the process.

After damage and injuries have been assessed, the coxswain must determine whether to continue with the mission or return to the unit. The following factors should be considered:

(01) Condition of crewmembers, (02) Overall material and operating condition of engines and boat structure, (03) Condition of electronics, particularly communications, (04) Urgency of mission, and availability of backup resources, (05) Likelihood of another rollover if continuing on mission and how it will impact crew, boat and mission outcome.

Remember that after a rollover has occurred, there remains the possibility of another rollover, since it is likely that similar conditions still exist. Upon returning to the Station, post-knockdown/rollover procedures must be taken in accordance with the specific Boat Operator’s Handbook.

Prior to entering the surf, a complete round must be made of the boat as follows:

A Coast Guard Surfman is a highly trained, highly skilled boat handler who understands surf behavior and characteristics. Since surf is not characterized by height, but rather by several waves or swells of the sea breaking on the shore, shoal, reef, bar, or inlet. The Coast Guard requires a qualified surfman, in a surf capable boat, to operate in a surf zone when the surf exceeds 8 feet, when the CO/OIC deems it’s necessary, or if there is doubt from the coxswain as to the present conditions.

Breaking waves cause aerated water in the surf zone. As the wave breaks, it combines with air, creating whitewater on the face of the breaker. As the breaker moves through the surf zone it leaves a trail of pale or white aerated water behind it which takes some time to dissipate. This air-water mix can create changes in a boat’s handling, which must be taken into account while maneuvering.

A boat’s propeller(s) will not create as much thrust when operating in heavily aerated water. The boat’s response may be greatly slowed. This effect can be recognized by:

(01) Poor acceleration and/or apparently slow throttle response, (02) Cavitation and/or excessive engine RPM for a given throttle, (03) Poor turning performance, particularly on a twin propeller boat.

A boat’s rudder(s) will not direct the propeller force as effectively in aerated water, nor will it have as much steering affect while moving through aerated water. This affect can be recognized by:

(01) Poor turning response, (02) Reduced steering effort, or “light rudders”.

Waterjet drives will have a reduction in thrust when operating in aerated water. This is caused by the aerated water being drawn into the intakes and being discharged at high speed through the jet nozzle. While not quite as pronounced, think of the way a garden hose that has been sitting in the sun and how it sputters when you first turn it. The normal stream that is used to maneuver the boat is not as effective because of the aerated water . This will cause:

(01) Decreased acceleration, (02) Increased engine RPMs, (03) Poor turning performance.

Operation in very shallow water can be complicated by a serious effect on a boat’s maneuverability. This effect, caused by resistance to the bow wave as it contacts the bottom, and drag due to the closeness of the bottom to the boat’s hull, propellers, and rudders, can be recognized by:

(01) Reduced speed over ground, (02) Reduced engine RPM for a given throttle position, (03) Sluggish response to throttle and steering inputs, leading to poor acceleration and poor turning ability, (04) Larger wake than normal, (05) Jet intakes may be fouled by sand or other debris limiting maneuverability, (06) Change in trim caused by the bow riding up on its pressure wave, and stern squat caused by propeller suction. This change in trim can lead to grounding of the stern if the water is shallow enough.

The effects of operating in aerated or shallow water are similar to the symptoms of serious engine,

NOTE

reduction gear, or steering problems. Any indication of systems trouble must be investigated as soon as possible once safely clear of the surf zone.

Changes in center of gravity or trim can lead to dramatic affects on the stability and handling of a boat in the surf. These changes are caused by either external or internal forces, and can vary widely depending on condition, type of boat, and other factors.

The primary external force for surf operations is the surf itself. A boat’s position, speed and heading relative to a wave will dictate the effects on stability and handling. These effects are numerous and will not be covered entirely, but a description of the most significant effects is provided.

As an approaching wave reaches the stern, the stern will rise and the center of gravity and the pivot point are shifted forward. As this process develops, the trim of the boat changes and may reach a point where the waterjets/propellers and rudders are no longer deep enough to be effective. This can cause a severe reduction in maneuverability or complete loss of control as the stern picks up and falls to either side in a broach. This effect is most common on very steep swells or breakers. It can be greatly amplified if the operator reduces power, which causes an even greater shift in the center of gravity.

As the approaching wave reaches the boat, it will cause it to heel over and shift the center of gravity to the low side of the boat. This may lead to a reduction in effectiveness of the waterjet/propeller and rudder on the high side, which will cause reduced maneuverability.

As the approaching wave picks up the bow, the center of gravity and pivot point will shift aft. If the boat does not have enough way on, and the bow is not sufficiently square to the wave, it may cause the bow to fall to one side or the other as the force of the wave pushes it around the new pivot point.

There are numerous internal forces that affect the stability and handling of a boat, many of which are permanent aspects of the boat’s design. It is the responsibility of the operator to be familiar with the characteristics of the specific boat in question. The following is a description of those factors that are subject to change, or are under the direct control of the operator.

Loose equipment can be tossed to one side and affect the boat’s stability by placing weight off center. Loose equipment may also result in loss of watertight integrity by breaking windows or damaging watertight fittings.

Generally, a rapid reduction in power will result in a forward shift of the center of gravity, while an increase in power will have the opposite effect. Large steering inputs will cause a boat to heel over, shifting the center of gravity to the low side.

A pitch pole is when a boat is inverted end-over-end. This can occur when a boat is traveling stern-to a very steep breaker or large wave. As the stern is picked up, the boat begins to surf down the face of the wave. This will cause the center of gravity to shift forward. If the stern rises high enough, the bow will begin to dig deeply into the trough of the wave, and the resistance created will cause the boat to trip over itself, tumbling end-over-end. A reverse pitch pole is also possible if a boat is surfed backwards while bow-to a large breaker. Pitch poles are rare, but are possible, particularly for a relatively boat. More often, an impending pitch pole will turn into a broach and knockdown/rollover. The operator must avoid those situations that could lead to a pitch pole since they are violently destructive to the boat and its crew. Broaching and a resulting knockdown/rollover are preferable to pitch poling.

The following description of techniques has been organized to follow the sequences of an actual operational situation, such as entering a beach surf zone to recover persons in the water, or crossing a bar or inlet.

General procedures for entering a beach zone or transiting inbound a bar or inlet with surf on stern are outlined as follows:

It is preferable to transit the surf during any lull period that may exist. The operator should wait until the last big wave in a series has passed and proceed in closely behind it, at maximum safe speed. This reduces the relative speed at which the waves overtake, gives the operator more time to react and gets you through the zone as quickly as possible. It may also provide the best maneuverability for some boats. The operator should attempt to work through the surf zone by driving through windows and wave saddles, thus avoiding the majority of the breakers. Some boats may be fast enough to avoid breakers by maintaining position on the backside of a swell while others will be overtaken by approaching waves. If operating in an area of limiting maneuverability, such as a narrow inlet or bar, the operator may have to rely strictly on timing the waves and make the transit during lull periods. To deal with an overtaking breaker or peaking swell, there are a number of techniques, which vary in success and safety based on conditions and type of boat. An operator must understand the effectiveness and safety of a technique for the specific boat, which is gained from training experience. These techniques are listed in descending order of preference and safety:

(01) Maneuver left or right (lateral) to avoid the breaker completely, by using windows and saddles, (02) Come about in sufficient time to meet the breaker bow-on, (03) Reduce speed before a steep, peaking (not breaking) swell reaches the boat, allowing the swell to pass and break ahead, and then immediately increase speed to follow it in, (04) As a wave approaches, begin backing square into it. Gain sternway and climb the wave before it breaks. Never allow the boat to be caught under a breaker. If it is necessary to back through the whitewater of a breaker, gain sternway before the whitewater reaches the propellers and rudders. Move smoothly into the wave as it lifts the stem, using only enough power to maintain sternway. The momentum of the boat will break it through the wave. Once the stern breaks through, ease off the throttles and prepare to resume the course ahead, (05) If the boat is overtaken by the white water of a breaker, the last resort is to try to get off the wave by applying full throttle, and steering for the “low side” of the wave, hopefully coming out the backside. Do not attempt to ride it out by maintaining course. Something must be done. Never forget to drive the boat, (06) A final option may be to back into the surf zone or across the bar, keeping the bow into the seas. This will be very difficult and time consuming. Excellent backing skills are mandatory. Strong opposing currents in the area may make backing impractical. Also, great care must be taken in shallow water, as the propellers and rudders will hit first if the boat strikes bottom.

Reducing speed after the wave has already picked up the boat will likely result in a loss of control and/or broach. Speed must be reduced before the wave arrives.

NOTE

If there is no discernible lull, it is prudent to remain at sea while waiting for bar conditions to improve (i.e., flood current).

General procedures for transiting with surf on a beam are outlined as follows.

This maneuver is safe only in small conditions and must not be attempted if the operator has any doubts. Wave avoidance is still the preferred technique.

It is preferable to make a beam transit during a lull, when the seas may be smaller. Wait for the last big series of waves to pass and commence the run. In the absence of lulls, great care and patience must be exercised, because the boat is very vulnerable with the nearly constant beam surf. The operator should use maximum comfortable speed to minimize exposure to beam seas. Speed may be reduced to allow waves to pass ahead of the boat, or increased to avoid a breaker. Good timing, and ability to read several waves back are critical. Any significant waves, which cannot be avoided, must be taken bow-on. There are several techniques to deal with breaking seas on the beam. The suitability of a technique is dependent on the boat type and present conditions. The operator must have an understanding of the boat’s capabilities, as some maneuvers may not be safe or effective in all cases. The following techniques are listed in descending order of preference and safety:

(01) When it is apparent that the boat is about to be overtaken by a breaker, retain or increase speed and turn to meet it square with the bow. Once square to the wave, the helm must then be returned to amidships and throttles decreased to avoid launching through the crest. Station keep if necessary, and prepare to return to original course. (02) If a breaker is approaching from ahead of the boat, decrease speed to allow it to pass ahead. Time the maneuver to reach the back shoulder of the wave just as it passes in front. This timing will allow quickly getting behind the wave and continuing the transit, and hopefully avoid the next wave altogether. The crew must be alert for other waves building off the beam. (03) If a wave is some distance off the beam, it may be possible to outrun it by increasing speed. If there is any chance of not beating the wave, turn to meet it or run away from it if space and time permit. (04) In some instances, there may be time and room available to find a window by running away from a breaker by placing it on the stern or quarter. This carries all the risks associated with running stern-to, and will also set the boat off the original track line or range, as well as being time consuming. It is not the most efficient means of transiting, but may be a valuable safety maneuver depending on the circumstances.

When transiting very small surf relative to the size of the boat, it may be possible to maintain or slightly reduce speed and simply turn towards a small breaker at about a 45 angle, resuming course behind it after crossing the crest. Do not get surprised by a breaker on the beam while watching ahead, as there is a good chance of a knockdown/rollover if hit on the beam at slow speed.

Station keeping is maintaining a given position in the surf. Station keeping is necessary to hold position while waiting for a window or lull, or holding position prior to and during recovery of a PIW. Environmental factors such as the surf, wind or currents can make station keeping difficult. Therefore, good backing skills and proper application of power are essential. The following are guidelines for station keeping:

(01) Use only enough power to maintain position and counteract the force of the oncoming wave. On smaller waves, keeping the bow square with neutral throttles may be all that is needed, while larger waves may require a great deal of power to counteract, (02) Using too much power will set the boat out of position and/or launch the boat. Too little power will cause the boat to be set backwards, or broach the boat, (03) Keep the bow as square to the seas as possible, (04) If the boat is being set towards the seas by current or wind, it may be necessary to back down frequently to hold position, only applying forward power to meet oncoming waves. Wait until a wave crest passes and back down once on the backside. Do not back down on the face of a wave, (05) By adjusting power, it may be possible to safely allow a wave to set the boat back to regain position. This technique requires practice, and the operator must maintain control of the maneuver at all times, (06) It is possible to move laterally while station keeping by allowing the bow to fall slightly to the desired side and then using the throttles and helm to straighten out as the wave pushes the bow.

For example, to crab sideways to port, allow the bow to fall slightly to port and as the wave pushes the bow, apply power and steer to starboard, finishing the maneuver with the bow once again square to the seas. This maneuver must not be attempted on large waves, and it is important not to allow the bow to fall off so far that the safety and control of the boat are compromised.

An outbound transit of the surf may be necessary in crossing a bar/inlet or departing a surf zone. The operator should practice wave avoidance by picking a course through the windows and saddles, if available, minimizing risk to the boat and crew. The transit should be made at maximum comfortable speed adjusting to avoid launching over the waves or avoiding them entirely. The following guidelines apply to an outbound transit:

(01) Choose a course through windows as much as possible, zigzagging as necessary to avoid breakers. Stay close to the shoulders of the waves to take advantage of any window that may open up behind the wave as it passes, (02) If a breaker cannot be avoided, try to go through the wave at the saddle, where it may not be breaking yet, or the force may be less. If both ends of the wave are breaking towards the saddle, the boat may be caught in a closeout. Get through the saddle before it closes, or slow down to let it closeout well in front of the boat.

Any breakers that cannot be avoided should be taken bow-on. Slow down and allow momentum to carry the boat through. Do not meet breakers at high speed or the boat may plow into the face, or launch off the back, risking injuries or boat damage. Do not allow a wave to break over the bow while transiting outbound. If it appears that this may happen, either reach the top before it breaks, or slow down/stop letting it break in front of the boat and then regaining headway in time to meet the whitewater.

See Section G Knockdown and Rollover Causes.

If the boat is disabled

either by mechanical failure or after a

knockdown/rollover in or near the surf, it will be driven into the shore. If not already aware or on scene, a backup resource must be notified immediately. The best chance for survival is to remain with the boat but the decision on where to ride out the breakers, either in a survivors compartment or strapped in on deck, is one you should consider before being in this situation. Some factors to consider are:

(01) Size and type of breaker – While on deck the boat may survive repeated rolls in 20ft breakers but a crewmember on deck may not, (02) Wave Period – do you have enough time to get into a survivors compartment, (03) Location of your boat with respect to grounding hazards such as wash rocks, jetties and other hard grounding areas that have potential to hole the boat increasing risk if in a survivor’s compartment.

The chances of a knockdown/rollover or crew injuries can be reduced by taking the following actions:

Do not expose crewmembers to the likelihood of serious injury or loss overboard by sending them to the bow in surf. It may be safer to sustain a roll while waiting for a lull. This is a judgment call.

Bank cushion occurs only when operating in close proximity to the bank and refers to a boat being pushed away from the nearest riverbank. As the boat moves ahead in the river, the water between the bow and the near riverbank builds up high on the side of the boat, causing the bow to move away from the bank. The bank cushion affect is especially prevalent if the draft of the boat is nearly equal to the depth of the water, or in narrow channels with steep banks.

Bank suction refers to the stern of a boat being pulled toward the bank. As the boat moves ahead while near the riverbank, the unbalanced pressure of water on the aft quarter lowers the water level between the boat and the bank, forcing the stern to move toward the bank. This suction effect occurs most notably with a twin-screw boat.

The combined effect of bank cushion and bank suction may cause a boat to suddenly veer toward the opposite bank (see Figure 6-27).

[Illustration in the handbook: Figure 6-27 — Bank Cushion and Bank Suction Affects in a Narrow Straight Channel]

A single-screw boat going at a very slow speed with its port side near the left bank may lose control if veer occurs. Increasing speed and adding a small amount of left rudder will bring the boat under control.

A twin-screw boat, with its port side near the left bank, usually recovers from this sudden veer by increasing speed on the starboard engine, and adding left rudder.

Current is the horizontal flow or movement of water in a river. Maximum current occurs during runoff and/or high water and the greatest velocity is in the area of the channel. Restricted or narrow channels tend to have a venturi effect, in that rushing water squeezes into a passage and accelerates. Current in a bend will tend to flow away from the inside point (to the outside), creating eddies, counter currents, and slack water immediately past the point. This effect will build shoals at the point or inside a bend. The prudent operator will be alert to the changing current within a waterway.

In extremely narrow channels where bank cushion and bank suction are expected, the coxswain should proceed at a very slow speed, keeping near the middle of the channel and passing other boats closer than normal. In a meeting situation in a narrow channel, headway should be reduced but not enough to lose steerage. On approaching the boat, a small amount of right rudder should be applied to head slightly toward the bank. Shortly after passing the other boat, the coxswain should reverse the rudder and straighten up. A little right rudder may be needed to hold course against the bank cushion effect. Because of wash from passing boats, extreme caution should be used.

Bank suction, bank cushion, currents and wind are factors that affect a boat’s turn in a sharp bend in a narrow channel. Bank cushion and bank suction are strongest when the bank of a channel is steep. They are weakest when the edge of a channel shoals gradually and extends into a large area. Bank suction and bank cushion increase with the boat’s speed. Channel currents are usually strongest in the bend with eddies or counter-currents and shoaling on the lee side of the point. Speed of the current is greater in deeper water than in shallow water.

In a following current, the boat makes good speed with little help from the engines. When making a sharp turn with a following current, it is possible to make the following maneuvers:

(01) Hugging the point, (02) Staying in the bend, (03) Proceeding on the bend side, middle of the channel.

An experienced operator can accomplish any of the three; however, the third choice, called the “bend side, middle of the channel,” is the safest, and therefore, the preferred choice.

The operator makes a small turn toward the near bank to steer a straight course. As the channel begins to bend and the boat moves from the bank, less of a turn will be necessary. This condition is a signal that it is time to begin a full turn. However, slack water or eddies may be around the bend, making it difficult to prevent the vessel from steering towards the near bank, especially in shallow water. The current under the quarter may affect the stern and vessel steering (see Figure 6-28). To correct for this, the coxswain should apply additional power and helm/tiller to steer back towards the center of the channel, keeping the stern in the middle of the channel.

[Illustration in the handbook: Figure 6-28 — Hug the Point: Current Astern]

Staying in the bend is a turn in the bend away from the point that takes precise timing. If done too late, the boat may ground on the bank in the bend. If done too soon, there is extreme danger that a strong and sudden sheer will occur. The bank suction on one quarter combines with the current on the other quarter to give the boat the sheer. Also, the bank cushion under the bow will increase the sheer (see Figure 6-29). Again, to correct for this situation, additional power and helm/tiller should be applied to steer back towards the center of the channel.

[Illustration in the handbook: Figure 6-29 — Stay in the Bend: Current Astern]

Approaching the turn steering a course toward the bend side of the middle of the channel is the safest method when the current is following. By doing this, the boat avoids any eddies under the point and the increase in currents in the bend. The operator can also use the force of the current against the quarter to help in the turn. A following current will force a boat toward the bend side; consequently, the turn should be commenced early in the bend. Additional power and helm/tiller should be applied as needed to stay in the middle of the channel (see Figure 6-30).

[Illustration in the handbook: Figure 6-30 — Approaching Slightly on the Bend Side, Middle of the Channel: Current Astern]

It is always easier to pilot the vessel into the current rather than have the current off the stern. When making a turn into a head current, the coxswain should apply power and helm/tiller as needed to stay in the middle of the channel. Caution should be used when starting a turn. If started too soon, the head current could catch the bow and force the vessel down on the point side of the channel. If this happens, the coxswain should apply power and steer back towards the center of the channel and wait until later in the bend to commence the turn. Care should be taken not to wait too long before starting the turn. If the turn is started too late, the current could catch the bow and push the vessel towards the bend side of the channel. The stern should always be kept in the middle of the channel (see Figure 6-31).

[Illustration in the handbook: Figure 6-31 — Heading into Current]