If I can give you one very big piece of advise then it would be this......
redo the motor mount t get that coupling straight......reason being is as follows.....
A straight coupling will cause less drag on the motor and has a knock on effect of using less amps which will have an added bonus of a longer running time.
In your case it is a simple fix of packing up the rear of the motor..... hope this is of help
Dave
Yes I perfectly agree Dave, I would normally fit the coupling as straight as possible (see previous custom mounts), although on this test I just slapped it in to see about revs power and
WIEGHT.
Yes as Nordlys has also mentioned, my original concern with this setup was the weight and the lack of RPM on the Hectoperm.
I will run it on Sunday as-is, and go from there.
If it looks good, then I'll likely shorten the shaft by 30mm (to shift the weight down and aft), make a shorter brass/rubber UJ, straighten the motor mount, and just run the Hectoperm.
Else...
If this motor/prop is still not an acceptable solution, I had considered a belt/gear (plane style) reduction as suggested by radiojoe, and could use either the Marx 300GT or another high power motor with the reduction drive, which would have to be the solution.
If I have to source another motor, I'll likely go brushless with reduction.
I don't want this to be a superfast speed boat, but go at a fun speed for with a bit in headroom if I need it.
The main issue so far has just been overloading the motors due to large prop direct drive with an undersized motor.
So putting the weight to one side for a moment, assuming the Hectoperm is up to it with the prop/gearbox, it will hopefully be acceptable.
Rgds
Jon