Would a runing boat that is held in place in the water have more load on the motor then a boat that is running through the water?

Yes. I run outboards and stern drives every day in test tanks at work. They do much more work moving "dead" water than using that power to propell the the boat forward. For example a 50hp honda I have in a tank right now is running about 4800 rpm at w.o.t. Put it in the lake and it will run up to 6000 rpm at w.o.t. with a light load. However a boat stationary can be allowed to cavitate and take the load off the engine. The only real test is to run it the way it going to be used.

Thats what I figured. Ok next question and some of the dyno guys might ne able to tell me. Can a heavy fly wheel be used to simulate to some degree the load on a motor when its in the water. If so how big would it have to be. Im trying to figure out a way to be able to bench tune a motor before putting it in the water.

Ok just answered my question myself. Yes a fly wheel will work. Im not looking to build a dyno. Im just wating to figure things like max rpm and getting a rough tune on the pipe and carb. Then I could see what mods effect max rpm.

WOuld never be the same 'load' as on water too many variables - even a change in strut height or props will affect load and may need to retune again - hope it works for ya

Cheers

RD