21ft Pontoon and Force 50 = 18 MPH

[smoedog]

I have a 21ft party barge with 96 Tracker/Force 50. It has a solas 11.5x11p prop on it. Took it out for the first time and i got 5200 RPM (stock speedo, not other way yet) and a GPS 18 MPH.

Best I can find on the net is it has a 2:1 Gearbox. So that give me a 33% slip. I was having problems with the prop blowing out trying to trim up. But it seems to me that the motor is mounted to low and while under way the top plate was about level or maybe an inch under the water. So any advice? I mean the speed seems good, but I dunno? Next time out I'll be marking it to see if the hub is slipping, but should I bother raising the motor up a notch or what?

 

[Bob_VT]

You are exactly in the area that would be expected with that motor. That is about the average for a 50

 

[smoedog]

Ya, I figured the speed was spot on. Should I mess with the motor height or just leave it alone?

 

[smoedog]

Ya, I figured the speed was spot on. Should I mess with the motor height or just leave it alone?

 

[ronward]

If you raise it up your ventilation issue will likely get worse. The idea is to have it as high as possible without ventilating. Sounds like it's about the right height. In your situation a fin may help.

 

[Silvertip]

On a pontoon you want the prop running in water that is as undisturbed as possible -- and that means deep. Especially with low power engines, mount the motor as low as possible so you have more liberty with trim settings. 33% slip on a "barge" is fairly typical. Be happy with what you have. If anything, lower the engine if it's not already full down on the transom. If you had a tri-toon and 100+ HP the requirements change.

 

[steelespike]

The good news is I think that may have a Mercury leg so props may be easier to come. You might consider the Merc
Spitfire,It's a 4 blade that appears to deliver 4 blade performance with 3 blade speed. The Spitfire is a straight change 11" for 11" when rpm is correct as yours is.
Your somewhat high slip may be the result of an inaccurate tach.reading a little high.
My info indicates 1.83 gear ratio from the 96 merc Chart. I get 39%
Pontoon results are all over the place,prop sizes,speeds and slip.was your speed with a light load just you aboard?
As you add weight to a pontoon it really affects speed.
You might try adjusting the trim.As you said adj. to the least venting My experience with pontoon trim is the same
You might try different weight distributions.If it squats too much may have more drag.
If the Spitfire has less venting you might try raising the motor.

 

[smoedog]

Its hard finding solid info on this motor. Its a 1996 Tracker/Force/Mercury 50 ELPT Serial #OE177142 The run was just me and the wife. I plan on getting a tiny tach or something equivalent. But this is the first time splashing this boat and still got a few small things to work out.

 

[steelespike]

iBoats prop chart indicates the Force and Merc are same props 95 on..I would suppose Mercs 1.83 ratio would be used.