3 or 4 blade prop for 9.9 hp 1976 Evinrude

[jbsimpson]

I have a freshly rebuilt 9.9 Evinrude on my 14ft Flat bottom duckboat (Jonboat). The motor runs great but the prop is original and I am getting ready to replace it. The current prop is a 9.5X10 3 blade. I would really like to get a little more speed out of this rig if possible. First, can I put a 9.25X10 4 blade on it? Second, willit give me the little more kick I am looking for? Right now the boat planes good with 2 people and a dog but it drags a little when there is no weight in the front, would a 4 blade help with this? Basically what are the advantages/ disadvantages to a 4 vs a 3 blade propr for a rig like this?

 

[steelespike]

Re: 3 or 4 blade prop for 9.9 hp 1976 Evinrude

Generally a 4 blade is used to improve low end performance usually at the cost of top end.Also used in specific applications like very heavy boats or pontoons.The 10" pitch is near the top of the prop chart would be expected to produce pretty good speed at the cost of some load ability.It appears your prop is doing a pretty good job.Dragging with a light bow is probably a weight distribution or trim problem.Trim in (prop closer to the boat)will plane easier and keep the bow down.Trim out and it
will be slower to plane and keep the bow up.There should be a point that is best for the light bow setup.If your pretty beefy you may need a tiller extension to get you farther forward.Of course you may want to put the tank in the bow.What is the bottom width of your boat?If your prop is not in excellent shape you should have it refurbished or replaced.

 

[jbsimpson]

Re: 3 or 4 blade prop for 9.9 hp 1976 Evinrude

The boat is @ 4' across the bottom at the back. You actually answered my question though thanks. I am fine on the low end. If a 4 blade is going to be worse on the top than what I have then I want to stay with a 3 blade. I just rebuilt this motor and I'm getting everything out of it that it can give. I was just looking for a little more speed. The more I think about it the high bow will probably fix itself when I have it full of decoys and I can always put my dog in the front too. Thanks for the help.

 

[dazk14]

Re: 3 or 4 blade prop for 9.9 hp 1976 Evinrude

A Solas Saturn stainless steel prop will be better in every way. About $116 at iboats.

Borrow a tach before you buy (important). I have found the Solas tends to run lower RPMs pitch per pitch vs. OEM. A 9" pitch might be the ticket.

Of course, you can keep your eyes open for a 15hp carb, but there's only a 2-3hp difference(my experience) and you must run the 15 at higher RPM's to get the most from it, although the same pitch as the 9.9 usually works fine - it simply revs higher.

 

[steelespike]

Re: 3 or 4 blade prop for 9.9 hp 1976 Evinrude

Very nice of you to respond but: its been 2 a half years since the last post.