Another Pontoon Prop Question / Engine RPMs

[crb340]

Read alot of info on props on this site but still have a question. Running a 10 3/4 inch prop with a 12" pitch on a 17" Odyssey Pontoon with a 50 HP Mercury 2 stroke. Max RPM is 5000. Originally I had a 10 7/8" prop with 9" pitch and was at 5600 RPM at WOT. However, I had cavitation problems (in a straight line when it hit around 5200 RPM). Still have cavitation problems with the 12" pitch but a little better. I also think that 5000RPM (which is the max RPM with the 12" pitch) is a little low based on my 2 stroke knowledge with Snowmobiles, Motorcycles, and PWC's but am not real sure about outboards. Not so concerned about top speed just would like to eliminate cavitation. Recently lowered the motor one hole in the mounting bracket (was originally in the middle of 3 settings) but have not had a chance to test (this probably lowered the motor about 1 inch). Any suggestions? Would a (fin, not sure of the exact name) that you mount to the bottom of the outdrive (just above the prop) help? or is this a waste of money.

Thanks for any suggestions.

 

[steelespike]

Re: Another Pontoon Prop Question / Engine RPMs

See if you can get the 9in. pitch cupped this should drop the rpm a little and give you a little better grip.Raise it back up and see what you get.

 

[crb340]

Re: Another Pontoon Prop Question / Engine RPMs

Not really sure what cupped means? I assume that I would need to take to a prop shop to modify?? Thanks

 

[steelespike]

Re: Another Pontoon Prop Question / Engine RPMs

Yes a prop shop, explain your problem and it was suggested a little cupping might help.