Trim angle and Aeration effect

Every boat is very sensitive to the angle of the engine shaft, set by trim, and RHIB boats are no exception. When it’s set wrong, this either sufficiently decreases the performance, or makes your boating much more risky. Try to find the most optimum and stable position for your engine, by adjusting the angle of the trim. Here are a few tips on how it works.

The engine is fixed too low – the bow goes down, splashing a lot.

The engine is fixed too high – the bow goes up, the hull loses contact with the water, decreasing stability and increasing the risk of being overthrown, and the propeller starts taking air, causing the propeller aeration.

The optimum trim – the boat goes straight, fast and stable, efficiently contacting the water surface while the engine shaft stays vertical.

*The AERATION effect, sometimes called “Cavitation”, means that the propeller is taking air with the following sudden engine RPM increase over the limit. You may distinguish it by the sound of the outboard motor howling on sharp turns or under similar circumstances. It is destructive to the engine itself, and it is disturbing to all the people around.

If it’s the wrong transom / engine shaft length or installation – check if the lowest boat bottom point to be at least 25-50mm (1′ – 2′) higher than the engine anti-cavitation plate. If it’s less – reinstall the engine lower, or use the engine with a longer shaft. Regarding the Aeration, the rule says: THE DEEPER – THE BETTER!

If it’s the wrong trim angle – just lower the engine, using trim or adjustable stop.

If it’s the poor balance and load organization – do not allow overloading specific parts of the boat.

Trim angle and Aeration effect
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