Motor trim is an integral part of boating, and helps your boat perform optimally, thus evidently reducing drag and saving on fuel. We conclude this two-part feature with a look at trim angles, gauges, steering and changing sea conditions.
Fine adjustments can make dramatic differences to how a boat handles, especially at sea. It takes a while to attune yourself to this and when you’re not familiar with a particular boat’s individual character, the rougher the water, the harder it is to discern actual trim angles.
Although grossly inappropriate trim angles are obvious enough, even experienced skippers habitually familiarise themselves with an unfamiliar boat. For the less experienced, a few simple exercises will reveal a lot about an individual boat and will meanwhile generate a much better understanding of trim and the adjustment of it to suit different conditions.
In any case, if a trim gauge or trim angle indicator is fitted (they usually are to boats with power trim and tilt, and sometimes aren’t with trim tabs), they’re a great help. Trim gauges are especially valuable in difficult circumstances where it’s not easy to perceive trim angles by the seat of your pants.
To accelerate to planing speed, nearly all hulls like their tabs down, and/or their drive leg trimmed in. So, to start our familiarisation process, trim the leg all the way in, and apply maximum downward angle of the tabs, then give the throttle a burst to boost the hull onto the plane.
Some boats will prefer a little less than all the way in trim or less tab than this. The best way to find out is to try it a few times, progressively trimming the leg out and the tabs up some more each time.
Keep trying until you find you’ve gone too far. That’s when the hull pokes its bow in the air and takes longer than it has been to reach planing speed. If you have a trim angle indicator you should be using it. Experiment until you’re familiar with the best trim angle for acceleration to planing speeds.
Once comfortable with that, go to planing speed and progressively trim the leg out, and/or the tabs up. This will lift some more of the hull off the water, reducing drag and increasing speed.
As a rule of thumb, an indication of good calm water trim angles is when the steering goes light. Try it a few times. Trim in/down and out/up until you feel this freeing or lightening in the steering.
If you keep on trimming out, the propeller will eventually reach an angle where it goes too far and loses grip, revs climb and speed decreases. Knowing where this happens is important when adjusting trim for different sea conditions.
Then, find somewhere with plenty of room and not many other boats about and try some reasonably tight turns. You’ll find that trimming in prior to a turn allows tighter turns before the propeller loses grip. And trimming out for straight running gives more speed without applying any more throttle.
Need we remind you to be careful during this entire process and to be ready to ease off if things start getting out of hand. The idea is to discover for yourself what that dreaded trim button does, not to end up with an insurance claim!
Each side of the lightened steering effect there’s a range of trim angles used to deal with changing sea conditions.
When encountering surface chop, particularly in a smaller boat, it will deliver an unnecessarily bumpy ride if left trimmed at calm water angles. Ride quality is improved significantly by trimming in, lowering the bows and using the sharpest part of the hull to slice through — rather than crashing into the bumps.
When travelling upwind, trimming in has other benefits too. It helps counteract the lifting effect of wind under the bows, which can be quite noticeable in lighter boats. At sea, in trim also minimises the tendency of the bows to loft into the air as the boat crests after climbing the steeper downwind side of a swell.
In big swell conditions, it may become necessary to actually accelerate up the face of a swell and ease off for the crest, allowing the bows to drop gently onto the backside of the wave.
A down swell direction of travel is just the opposite. Travelling down swell, trimming out raises the bows to help the hull recover as it encounters the back of one swell after descending the previous one.
Minus out trim, the bows are more likely to bury and may veer uncontrollably to one side. This is known as broaching and it’s extremely dangerous. Broaching places the boat side on to the sea in a vulnerable position and the sudden change of direction when the broach occurs can be violent enough to throw the person at the wheel aside.
Correcting a broach is the same as correcting a slide in a car; that is by steering towards the original direction of travel or steering into the slide. The place to learn about trimming out to improve down-sea handling and reduce the chance of broaching is obviously and most definitely NOT in big seas.
Take the advanced course with common sense, and while you’re at it try out all the angles as well as directly up and down sea. Familiarise yourself with using out trim to reduce the tendency of the bows to bury when travelling down or down and across a sea, and how much in trim to use when travelling into or across and into a sea.
It goes without saying, but is worth repeating anyway: You should be completely au fait about loading your boat to trim it correctly and be comfortable using the trim adjustments provided on every planing powerboat to cater for changing conditions — before even thinking about going to sea.