Driving a boat under power is easy but driving her well is different, even though it doesn’t require expert maneuvers. All that most of us desire is to be able to slide so quietly into our berths that no one on shore notices our arrival, and the crew would never quite realize how it was done.
What happens to a boat when it is under power?
A boat is not guided by the movement of anything at her front end. She pivots about her center of lateral resistance. This means that if your vessel is lying alongside a dock you will never work her off tidily by shoving the helm over and motoring ahead. Before her bow can swing out, her stern must swing in and the bow swayed to come off the wall. Pivoting helps steer close around an obstruction or avoid imminent collision. Many buoys or piles have been struck by the stern of a vessel as her helmsman mistakenly turns her helm the wrong way,
When bringing a boat to rest beam-on to the wind, it pivots around her keel thus her bow invariably blows off downwind. The speed or distance may vary from boat to boat but this is certain. There will be no visible tendency to blow off except in the hardest cross-winds for the keel is biting the water. It is important to make necessary arrangements to avoid losing way in a final approach, either by allowing it or counteracting it.
Rudder action is obvious when moving ahead though the situation is less clear on moving astern. In theory, one should face aft when steering, then operate the wheel or tiller so that the rudder points in the direction you want the stern to swing. As any owner of a long- keeled boat will tell you, life is not often that simple. A fin-keeler with a deep spade rudder will at times steer well astern at very low speeds but this is not the case with some other boats. One must consider all the forces are acting upon the boat in order to compromise, the rudder being only one of them.
For propellers that are placed directly ahead of the rudder (it should be, and often is), it is simple to pivot your boat around her turning point when she is not moving ahead at all. Put the helm hard over so that the rudder is acting as if going ahead then give her a solid blast full ahead for a few seconds. Unless she is very light, she won’t gather any appreciable way, but the surge of water thrown aft by the propeller will be hurled out sideways by the rudder blade while the stern will be thrown in the opposite direction.
Rarely, there are propellers situated abaft the rudder and this effect cannot be reproduced by giving the engine a burst of power astern. None the less, a strong kick in reverse usually shunts the stern of a boat predictably one way or the other since only the propeller is at work. Let us refer to this phenomenon as ‘prop walk’.
When water is driven off a revolving propeller it spirals into a vortex and this creates a certain amount of sideways force, though it is minor when the boat is at stalling speeds. When she is not under way, particularly with the engine in reverse, the results are noticeable and often dramatic. The rudder is usually ineffective until the speed is increased. For the common ‘right-handed propeller’, the stern of the yacht will shunt across to port when the engine is put astern and vice versa for a left-handed prop. On some craft this can be so positive that it becomes a primary maneuvering tool; in others it is barely perceptible. What you need is to determine which way the stern will go and how hard.
The best way of finding this out is to run the engine astern while you are tied up. A glance over both quarters will be enough to indicate on which side the turbulence is greatest. Freed of the dock, the boat would naturally shimmy her stern away from the disturbance. The other way is to steer straight ahead in calm water, put the engine out of gear and let your way fall off. Then, before coming to a stop, put the propeller half astern and observe the direction the boat will swing.
To turn tightly when moving forward, either make the nun while carrying away or do it with the gears and the propeller engaged throwing water over the rudder blade. The latter generates a shorter turning circle which decreases with increase in power. Since the vessel accelerates as it goes around, one requires skill to maneuver round other boats. If you ‘bottle out’ halfway round you might not make it, but if your judgment proves shaky carry on regardless and the bill will be heavier. The power turn is not for the fainthearted, but in competent hands it can be a problem-solver.