Stoner,
Yeah the exhaust into the water worked a treat for this engine, very loud when it skips out of the water though! (2stroke which like a bit of back pressure).
However the ‘newest’ version is a 4-stroke which didn’t like the restricted exhaust very much, so I’ve moved it to be above water, interestingly with no noticeable noise increase.
These strimmer engines are used a lot in model boats, so there are a few specially designed props for them – i.e. props for very high revving low torque engines.
Cruises at around 5/6mph with 3 adults and 1/3 throttle, does 4-5km on 0.5Litres of fuel.
Funnily enough I was inspired by the Thai riverboats, – went on loads as a kid.