Prop size for pontoon/house boat

[beavertrapper70]

Ok, If anyone can help me on this I will be very grateful. I have a 35 foot Koyote pontoon boat. Actually, I don't really know if its a pontoon boat or a houseboat, because it has a 20 foot cabin on the deck. Regardless, the pontoons are steel, so its a heavy beast. I have a 81' Evinrude 35hp on the boat that I use on the river. The boat isn't fast at all, and I am not looking to gain speed, I just want to make sure I have the right prop. I currently have a 10-13 3 blade prop, and it appears to me and my other boating friends that the motor isn't running at full RPM. I have done everything else to try an eliminate a reason for running low rpms, including changing plugs, thoroughly going over the carb, and fuel system. I don't understand how prop sizing works, so I am hoping tht someone on here can tell me what to do. Ill be checking back regularly in case I need to provide more information.

Thanks again,

 

[Bamby]

Re: Prop size for pontoon/house boat

I take it your boat does not have a tech? It does sound as if your prop has to much pitch. Is there some way to hook up a tech as least on a temp. basis. Without rpm's any advice would be winging it. Please try to find a way to provide more info. so someone can give you some sound advice.
Gregg

 

[steelespike]

Re: Prop size for pontoon/house boat

No question in my mind a 13 is way too much prop. A 13 is only 3 from the biggest a 9 is only 2 from the lowest.Motor is rated for 5200 to 5800 rpm.
If you were making 5,000 (Highly unlikely)a 9" would only put you at 5,800.
If you could find one I think a 9" pitch might work.Perhaps you could borrow a shop tach to at least check your present rpm.I'm thinking a 7 would be better but try to get your present rpm.first.

 

[beavertrapper70]

Re: Prop size for pontoon/house boat

Ok guys, thanks for help so far. Whats my best option for getting my RPM's since I do not have a tach? Do they make add ons? Could a good multimeter possibly give me any information? This boat will never leave the river, and I need to test the RPM's in the river anyway, at least I think I do due to the current(I usually just idle downstream, or float) I know I have seen cheaper add on tachometers for lawn mowers, etc, would that work?
Thanks again for the help,