Re: Pontoon speed help
I've seen them recommended here and on other forums in several posts, can anyone point me to somewhere where I can buy a "pontoon specific", "elephant eared" or "extra cupped" prop? I believe these critters are a pontoon boat forum myth. I've seen props described as "elephant eared" for small, under 20HP, merc outboards that are no longer available, and I have a Michigan Wheel that had "exrta cup" somewhere in the description but is out of production and has been for 20 years. I haven't been able to find a new or used prop with any of these terms attached to it anywhere on line or in shops.
To answer the OP's question, I would do as suggested, see if you can borrow a 19 or 21p prop and see what it does. If you try the 19 or 21 and still get that 6000 rpm then you do need to get the motor down, or back into some smoother water. Most 115hp, 21 or 22 foot boat owners that post about props are using 15 to 17P props. I hope whoever just built you a center tube with a built in transom thought about the fact that you were trying to get a little more speed out of your boat when you had it built.
I just added a 10 foot long 3rd tube and a 90hp Johnny to my 20 footer and I'm getting 25mph by GPS at WOT with an old Michigan Wheel 15P. The tach isn't working so I'm going tomorrow morning to get that fixed. I was getting 27mph with an OMC 17 but until I get the tach working I don't want to take any chances on lugging the motor down.