[keithet]

Hello,
I have an 18' Voyager pontoon boat with a Yamaha 40 hp 4 stroke. I have a Yamaha 11 5/8 D by 11" pitch prop. Using a Yamaha marine mechanics tach (which agrees with mine) I can get only 4700 rpms at WOT. The mechanic has verified all is running well and compression, fuel pressure and timing is fine. It starts easily and smooth idles at about 900 rpm. 5000-6000 rpm is supposed to be WOT limits. Any suggestions or comments would be appreciated. Is 4700 rpm close enough? I don't want to go stainless.

[steelespike]

Well its obvious you need about 1300 rpm.
If the dealer set you up they should let you try props till they get it right.
I would start with a 9 and see what it gets you.Props are available here down to 7".Some in 4 blade.Rule of thumb 200 rpm per inch But on smaller motors this could be higher.If the 9 puts you well within the rpm range maybe stick with it to try to maintain some speed.
You could try raising the motor a hole, might get you a little rpm.
Also try different trim settings do one thing at a time.