One might take a new look at air cooled engines. I have little choice
as one of my "mud boats" may be crossing a mudflat a mile or so from
the nearest water, and then turning up into a rapid river. I use a
radiator for cooling if I build using a water cooled engine.

My latest craft has an EFI lawnmower engine, and gets very nearly as
good fuel consumption as a liquid cooled engine. Air cooled is still
noisy, though not even remotely "English Seagull" noisy. Propeller and
fan noise is kept very low, as low blade tip speeds are used.

Barry Palmer, for Sevtec