[willdoss]

Hi,

I recently re-powered my 24 ft Grumman Pontoon boat with a 2008 90 HP Evinrude E-tec. The prop that the dealer put on is a 15 inch diameter 13.5 pitch stainless Solas three-blade prop. I anticipated that I would have to try out the prop and possibly swap to a different pitch so that's not a big deal for me.

Anyway at WOT, the Engine is only turning 4600 RPM, so the dealer suggested that we go with a 13 pitch three blade (the operating range for the Engine is 4500 - 5500 rpm.) I'm hoping to get 5200 - 5300 RPM at WOT.

My question is this, for pontoons, are 4 blade props a better choice? Can you justify the extra cost for a 4 blade in added fuel efficiency, stability, etc?

I know that this thing is never going to be a speed demon, it is, after all a pontoon, I just want the best prop for a pontoon application, with fuel efficiency being the most important factor.

By the way, even at only 4600 RPM the E-Tec 90 pushes this pontoon boat to 24 mph! At 3000 RPM it cruises at 12 MPH. The engine will push you back in your seat when it comes out of the hole too. Lots of power in a small 90 HP package!

[Dhadley]

There are props made specifically for pontoon boats. We're kind of assuming you mean the prop is 13 1/2" in diameter (not 15") and the pitch was 15, now looking at a 13. Most of the pontoon props for your motor will be in the 14" diameter range. The blade shape and rake angle are different too.

If your dealer is having trouble finding one, shoot me an IM or email. We can get you headed in the right direction to find one.

[steelespike]

Generally the prop that pushes the boat fastest will produce the best mileage.
Your 90 will use about 9 gph(gallons per hour)@ wot(wide open throttle)
The farther the boat goes in an hour the better the mileage.
The toon doesn't plane so best mileage usually is between 6 to 9 mph.
not the most practical speed so you need to select the speed that best suits your needs.
There are 4 blade props that are specifically for heavy hard to push applications.Sometimes a 4 blade is recommended for venting(cavitation) problems.Rule of thumb says a 13 would put you at about 5,000
If your not having any problems with venting you might consider raising the motor one or two holes.Won't gain you too much but the less dragging through the water the better.Careful adjustment of trim might help as well.

[willdoss]

Thanks for your comments, I really appreciate them.

As far as lowering/raising the mounting bracket, the engine does have power trim, but raising the engine any significant amount causes cavitation (again, a characteristic of pontoons) I can raise it a little, but not much.

[willdoss]

The prop has 13.5 x 15 engraved on the outside of the hub, I was assuming that 13.5 was the pitch, but, as you said, its the diameter.

So you are saying that most pontoons use 14" diameter props? Maybe I should try a 14 x 14.5 or maybe go to a 4 blade and try again?

THanks for the help!

[Dhadley]

The 14 is about as big as you can go on that gearcase. The 14 1/4 to 15" diameter props are for the V6 style cases.

[steelespike]

Originally Posted by willdoss

Thanks for your comments, I really appreciate them.

As far as lowering/raising the mounting bracket, the engine does have power trim, but raising the engine any significant amount causes cavitation (again, a characteristic of pontoons) I can raise it a little, but not much.

Perhaps if you get a dedicated pontoon prop you could get a little more height.Again on a pontoon probably won't gain much but every little bit helps.

[willdoss]

Thanks Steele,

After reading other posts, I'm happy that I can turn at WOT and not cavitate!