I'm not talking about you guys, I'm talking about the select few who troll the forums.
There is more to the hobby of rc boats than race boats and racing.People forget that.
Water cooling is an issue. but there might be something that can be done.I've just run aircooled and don't have problems.But water cooling is not a bad idea.
There was a guy in Australia that tig welded some flat stock around the the top end forming a water jacket, it worked but wasn't pretty. Not every has a tig and can weld non ferrous.
So leaves a couple options that can be done with basic tools. One is wrapping the top end with soft tubing. I'm going to try that on this project.
The other is using flat stock and some JB welded screwed together for a water jacket.
On the Honda you have the option of also cooling the oil reservoir.
I prefer the Honda to the rest, but another engine that would work is the Robin /Subaru.A number of years ago I reviewed all the mini four strokes on the market. Some I bought to get a first hand look.I didn't even consider cantilever crank engines and flat head engines.
At this time the only engine I recommend is a Honda.Parts are easy to get.
3 obstacles are motor mounts,collet and throttle linkage.None are off the shelf but can be made from existing parts or with the mounts, a hack saw and hand drill with careful measuring will give you good mounts.
Speed wise a stock Honda GX25 in my 57" TS mono went 24.6 mph
A stock GX35 in the same boat went .5 mph faster.
The reason is the engines are rpm limited with small carbs. There is no rev limiter in the Honda ignition.
RPM is limited to about 7500. Simply swapping carbs and some basic porting will let it rev to over 9000 this is with a Prather 280 prop IN THE WATER. I don't quote rpm I get on the bench.
Heres a pic of the TS mono with GX35 that had mild port job, bigger carb and mild cam. ran 33-34.