Choosing prop for 9.9hp

[pgdignan]

Anyone, if I'm replacing a prop on a 9.9 I have a myriad of options from an 11" pitch to a 5" pitch and of course 3 vs. 4 blades. Planning on building one of those small mighty mite hydroplaner jobs over the winter, any advice as to what I should choose for best performance

 

[rndn]

Re: Choosing prop for 9.9hp

Use whatever prop will operate within the manufacturer's specifications rpm's at WOT on the boat you will use it on.

 

[steelespike]

Re: Choosing prop for 9.9hp

When building your boat set it up so you can easily adjust the verticle height.
You'll want it as high as possible and still pump water and not ventilate to easily.Start with the prop you have and check the rpm.RPM range prior to 89 is 5,000 to 6,000 89 is 5,500 to 6,500.I assume the newer ones are in that range.Technically a 2 blade prop is the most efficient.Probably difficult to find.
stay away from the 4 blade as there is too much resistance.Once you know your rpm you may be able to go with more pitch and or get the prop cupped at a prop shop.Cupping will allow more height and is usually more efficient.
If available a stainless prop is more efficient.A stainless will drop your rpm some.

 

[BF]

Re: Choosing prop for 9.9hp

My '82 15 hp OMC has the standard 9x9 prop on it. It does well pushing standard aluminum utility boats around. With a lightweight hydroplane, I'd assume a 9.9 would be able to handle a 9" pitch for sure, probably more (?) 10 or 11"? So, I'd GUESS that a 10 or 11 would be right, but as others have said, WOT RPMs will tell you for sure.

I'd check to see what the "standard" pitch is for your year/make motor, and go up one or two inches in pitch from there. The standard one will be intended for use on a typical boat.

The 5" pitch prop is probably for a pontoon or a sailboat. Maybe if you google one of the boats you're building, you can see what someone else is running for pitch with a 9.9(?).