Boat engine removal, rebuild, refitting and first start

[Gilbertd]

Porpoising a bit there mate, you need to trim the bow down a bit. That will stop it and increase the speed without increasing the revs.

[LPGC]

Porpoising a bit there mate, you need to trim the bow down a bit. That will stop it and increase the speed without increasing the revs.

I know what you mean and do know about using the trim etc. It's difficult to tell from the video but some of it wasn't easily avoidable due to the waves unless I changed direction and/or speed.

Max speed and fuel economy for engine rpm on some boats is with it trimmed up a bit from fully down and that's true of my boat, I've confirmed it on flat water using a GPS speedo. I think that's because the front of the boat is always higher than the rear in the water so trimming up a bit keeps the prop more parallel with the direction of travel and not 'wasting' forward thrust pushing the back of the boat up or down instead. I usually trim fully down to get on the plane but try trimming up a bit once up on the plane to try to find a 'sweet spot'.. For me the sweet spot is what seems the best compromise between speed / rpm / fuel efficiency / how it handles the waves and is effected by the sea conditions, direction, speed, how the boat's loaded, etc, and preventing porpoising. Trimming down makes the bow ride lower (and steering better) and the bow is shaped to cut through waves but you don't want the bow to ever 'fall off' a wave and be close to going under the next wave lol. Trimming up makes the bow ride higher so less chance of the bow going under the next wave but can be harder landings after going over a wave and makes porpoising more likely. Quite a lot of weight in the back of the boat with my sister and kids in the back while she did the filming and I did have it trimmed near fully down at that point but it rode better when she came up front. To a minor extent trim may also effect mechanical aspects such as how straight the universal joints between the engine and drive are.