My experience with air cooled inboat engine is with 4 hp Bernard engines. They were still common in my childhood in the 80-ies and 90-ies. The sound is deafening and the only way for anyone in the boat to avoid damaging one's hearing severely was to wear earmuffs every minute the engine was running. A 4hp air cooled Bernard at a distance of a half nautical mile to windward makes roughly the same noice level as there is inside a boat with a water cooled engine.
This is the reason why I hate air cooled boat engines.
Though nowadays everything is air cooled and hence unsuitable for boat use.
Maybe it would be possible to cast and machine a custom engine block for a modern motor so it can be converted to boat use.
Another problem is the ignition magneto. In a boat engine the magneto must be mounted high up and well away from the flywheel. Every now and then there will be bilge water reaching the flywheel and being thrown around. If the magneto is inside the flywheel it will inevitably break down every time that happens. Usually the bilge water rises and sploshes around up to flywheel level in bad weather when the planking flexes a bit and a few bucketfulls of water come over the gunwale every once in a while. Exactly the sort of condition when you don't want to drift downwind for hours while pulling off the flywheel with a gear puller and rebuilding the ignition magneto.
Honestly I am pineappled of with thoughtless motor designers.
Sorry, wasnt sure what size you needed and clicked on the first in the list. Though they have others at much lower HP.
