prop question

I have a 96 SunTracker 21' with a 70 hp Yamaha. It has an aluminum prop and I can't find any numbers stating the pitch. It will run about 17 mph with 500 pounds of people on board. Does this sound about right. It jumps right up to speed and I'm wondering if I'm leaving something on the table with power over speed.

Re: prop question

That is a decent speed with that load. I don't know much about Yamaha props the guys over in the prop section may be able to help you.

But the type of a hull a pontoon has takes a lot more power to push it. and WAG I would say you have 2 toons of around 24 inch OD. So your about in the right speed range.

Re: prop question

You'll need to get your actual WOT RPM (usually with full tank of fuel and two people aboard) and the engine's recommended WOT RPM range to determine if you have teh correct prop.

Re: prop question

craigmack said:

You'll need to get your actual WOT RPM (usually with full tank of fuel and two people aboard) and the engine's recommended WOT RPM range to determine if you have teh correct prop.

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+1 ^^^. 17 mph w/ that setup sounds about right. Good luck !!!

Re: prop question

Pretty much anyone selling props has a prop calculator. I have an 18' 2012 Party Barge with a 75hp Merc. WOT (wide open throttle) is 5500 to 6000 RPM. I experimented with 3 props, 13, 15, and 17 pitch. 15 and 17 pitch would only get me 4000 to 4500 RPM, and the 17 would cavetate. The 13 would turn 4600 RPM and run 24mph (gps). It is all about numbers, the faster the prop spins with the maximum pitch, the faster the boat goes. Too much pitch and the prop won't turn, lugging the motor. Too little pitch, the engine will over rev, or the rev limiters will kick in. Either case, you go slower. 1 change in pitch can / will change your RPM 400 to 600 rpm, give or take.

Good Luck

Re: prop question

You will find a number on your prop if you pull it off the motor. If you cannot find a number on the barrel or where the nut and washers are, it will be on the hub side of the prop. Sometimes you've got to clean a prop with bleach water to see some numbers.

Like was said, you need to prop your boat where it will pull 90%-100% of the factory redline when loaded as you run it most of the time. Most 2 strokes redline @ 5500-5800 rpms. And you've got to make sure your motor's running 100% of it's capability.

Good luck!

Re: prop question

mb4859 said:

I have a 96 SunTracker 21' with a 70 hp Yamaha. It has an aluminum prop and I can't find any numbers stating the pitch. It will run about 17 mph with 500 pounds of people on board. Does this sound about right. It jumps right up to speed and I'm wondering if I'm leaving something on the table with power over speed.

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We had a 22ft toon with a 60 yammy on it and did 21mph by gps. I would think that you should get at least that.

Re: prop question

The WOT rpm range you're looking for is 4500-5500 rpm for your Yamaha 70.

Re: prop question

Pontoon speeds are all over the place. For no obvious reason accept a pontoon is really hard to push.
While 17 is acceptable I think with careful setup and the right prop 20-21 is possible.
A lot will depend on your present prop size,wot rpm and speed by gps.