Ok, here it is boat starts great the first time and runs well, shut it off and won't start again on water, tried 2 starters same result, but motor started on hose when i got home, then ran to lake started right up, drove around 13.5v output. Shut off wouldn't start again, took home put on muffs started right up. Have new gel cell battery. Compression checked out 100-102 all cylinders. Possble grounding problem, i can't figure this out

I'm still pondering, is my motor too low and getting too much back pressure, the idle exhaust ports are under the waterline

does it not crank at all, or just not fire up? what motor

Sounds electrical to me.

when you turn the key to start a second time does it make any noise at all, clicking, buzzing noises?
does it turn over but not fire?

Sounds like a carburator float or choke problem. Choke might be sticking or float sticking and flooding the carburator.When it cools off the flooding clears up and it starts!!

sounds like a bad ground on the new starter you need to clean at least one of the holes the starter bolt goes thru to bare metel especially if the bolts have washers

run a set of jumpercables from batt to starter and to ground to block ground