Fore-and-aft trim
Leg out or trim up = bows up
Leg in or trim down = bows down
Faster power craft Trim
Most planing power yachts and semi-displacement fast cruisers have the facility to adjust their fore-and-aft trim mechanically. This is achieved either by varying the angle of an out-drive or outboard, or applying trim tabs sited right aft, one on either side.
‘Leg in’ or ‘trim down’ keeps the bow down. ‘Leg out’ or ‘trim up’ encourages the bow to rise. ‘Trim down’ on one side only will persuade that side of the boat to ride high, discouraging rolling and helping her to deal with a beam sea. Stowage – The motion of a fast motorboat driving into a head sea can be literally shocking. There is a certain amount the helm can do about this, but it’s inevitable that both boat and crew are going to submit to something of a beating. Anything up forward is going to be well scrambled, so extra care needs to be taken to stow lockers tightly, pack crockery and glasses with towels, and generally make sure that nothing that could conceivably break loose has any chance of doing so. Crew must also be ready for a tough ride.
Head sea
A boat powering into a head sea, especially if she is planing, will try to take off on the wave crests and may plough into the trough so badly as to lose control. Fortunately, most boats today are of the deep-vee hull form. So long as the bow can be kept down to use as much of the waterline length as possible, the sharp sections will minimise any tendency to slam. This is achieved by trimming down or trimming the leg hard in.
Throttle back as you climb the front of the approaching wave to prevent the boat taking to the air over the top, then power up down the back to keep the bows high and stop them nose-diving as you enter the trough. Wave length – All of the above can be readily expedited if the wave length is long enough for such luxuries. Often, however, the seas are steep enough to create a challenge without being far enough apart for ideal set-piece manoeuvring. In such a case the best plan is to come off a dead upwind heading by anything from 30° to 45°, taking the seas broad on the bow instead. After a measured length of time, alter course to put the weather on the other bow and plug on until you have made up the difference. This tactic can make for a surprisingly comfortable ride, and the additional distance is far less than you might imagine, especially at only 30°.
Beam sea
Trim down on the upwind trim tab to raise this side of the boat a little and help ease the rolling. Assess the nature of the seas and in particular their regularity to decide how much way to keep on. Very often, a sea is confused and you may have to opt for a compromise between beam- sea tactics and those for a head or a following sea. The danger, as for the slower motor boat, is that you’ll be rolled by a breaker. With your extra speed, however, you have some capacity to see a bad one coming and take avoiding action by steering to pass to one side or the other. If taking a breaker becomes inevitable, either turn into it or swing away to try and outrun it; don’t just sit there like a duck in a shooting gallery and do nothing.
90 | MANUAL OF SEAMANSHIP
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