Diesel engines are used in a forceful manner on a yacht and manufacturers consider this when matching drive trains and propellers to specific engines. Yacht propellers vary greatly in size, shape and format, from the [ three-bladed ], fixed propeller to the [ variable-pitch propeller ] of heavy cruising yachts.
[ Marine engine controls ] are standardized to a single lever, which is able to select forward, neutral, and reverse gears in conjunction with governing the engine speed. Single lever handling under power is a more precise method than in the days of individual gear and throttle levers.
Modern marine engines are more reliable than their predecessors however, still allow for engine failure with an anchor ready, and sails ready to hoist. A yacht under power does not have the same steering qualities as a car and coupled with other factors affect boat handling to different degrees.
Novices to sailing make the mistake of assuming that a yacht steers in much the same way as a car. When a [ boat turns ], it pivots about a point near its centre, with the stern swinging out away from the direction of the turn. In a confined space, when boat handling, be aware of the stern's swing as the yacht is turned.
Boat handling expertly under power requires an understanding the propeller effect called [ prop walk ]. The lower blade of a turning propeller rotates in denser water than the upper blade (as water density increases with depth) thus creating a paddle wheel effect. This has a tendency to push the stern sideways in the direction or the propeller rotation. A right-handed or clockwise-rotating propeller tends to "walk" the stern to starboard when moving forwards. The direction of rotation reverses in reverse gear when the yacht is going astern, with the propeller "walking" the stern to port.
Going ahead, the rudder easily counters propeller walk after achieving steerage way. When going astern, the rudder becomes less effective on most yachts at slow reverse speeds with 'prop walk' or 'paddlewheel effect' becoming more apparent. It is wise to discover the extent and direction of of this effect when boat steering in reverse before leaving berth.
Having tied the yacht up securely, engage reverse gear at half throttle and watch over the side to see the direction water turbulence appears. This indicates the flow off the propeller and if free to move, the stern swings away from the disturbance.
Boat handling characteristics under power, depends on a number of factors such as engine size, propeller location and rotation direction, keel type and rudder, and the amount of windage above decks. Long-keeled yachts with their rudders hung on the back of the keel make boat steering difficult going astern and may be impossible to get the yacht to go astern in a straight line.
Know the yacht's limitations so that manoeuvres can be planned to avoid difficult situations. Wind effect on the boat helps or hinders boat steering. The wind blowing from the side pushes the yacht's bow downwind at slow speed. If this effect neutralizes the effect of prop walk or paddle wheel effect, reverse boat steering in a straight line is possible. Wind contributing to the prop walk effect, increases the effect and turns the bow rapidly downwind.
The wind on the high sides and cabins of a yacht assists or hampers a [ turn ] depending on whether the turn is away from or toward the wind. Knowing the characteristics of a yacht in this situation becomes important when considering a turn in strong winds. A turn toward the wind produces a wider, slower turn, and a turn away from the wind, a tighter, faster turn.
[Fin-keeled cruisers], especially those equipped with a spade rudder, steer astern effectively even at slow speeds. When boat steering this type using a tiller, be aware that when motoring quickly astern, the rudder forces can be strong and this force transmits to the tiller. Hold it firmly to avoid large movements or the tiller will be wrenched from the hand and swing violently to one side. When this happens, the yacht turns rapidly, causing the helmsman to be trapped by the tiller unless he stands clear of its end.
The use of the engine to manoeuvre in confined spaces requires learning the yacht’s behaviour in different conditions. Experiment with boat steering in a stretch of clear water in a straight line astern at different speeds and check the extent of propeller walk. See how tight a turning circle that can be achieved under full power, half power, and at low speed.
Propeller walk allows a tighter turning circle in one direction, often when turning to port, going ahead or astern. When motoring astern, the effect of moving the tiller is reversed with the bow swinging in the direction of the tiller with the stern moving in the opposite direction. Practice boat handling skills until proficient at turning the boat in tight spaces and plan for the unexpected with the anchor and sails ready for instant use.
The most difficult manoeuvre under power is turning in a confined space. If there is no space to execute a power turn with the helm hard over, turn safely under full control using slow-speed handling skills involving prop walk and wind effects.
With the stern moving to port under prop walk when going astern, start the turn to starboard by pulling the tiller hard over to port and holding it there. [ Engage the engine ] for a few seconds to start turning. With the rudder hard over, the water thrust from the propeller gets deflected by the rudder in turn making the stern move in the opposite direction. Engage neutral as the yacht moves forwards. Engage reverse and give another burst of power, keeping the tiller to port.
Prop walk or paddle wheel effect in reverse moves the stern to port. As the boat moves astern, shift into forward gear and give another burst of power. Alternating ahead and astern bursts of power from the engine with the aim to use the propeller thrust to turn without moving the yacht forwards or backwards significantly.
Another variable that affects boat handling is tidal movement, which can be used to advantage after determining the tide's direction. Facing into it and matching its speed allows the yacht to remain stationary.
In rare circumstances, an approach to a stationary object is made by moving with the tide. The use of reverse gear to stop or stay in position alongside the object makes it extremely difficult to steer and additionally, most engine/prop combinations do not produce sufficient power to combat a strong tide.
Boat speed should be regulated to the minimum needed to complete the manoeuvre efficiently, but moving too slowly may not be sufficient to counteract the effects of the wind or tide.
When picking up or releasing a mooring, the crew member must never have to take any weight on the mooring strop. When coming alongside a mooring, the yacht covers the last few feet in a sideways motion, allowing the crew member to jump off and fix the mooring lines without having to fight the weight of a moving boat.