RE: Pontoon Props

[pbxcomm]

RE: Pontoon Props

Hello all,
Question (and a second opinion)

I have a 21' Riviera Cruiser Pontoon, with 50 HP Johnson SPL and a Michigan Wheel 13" X 11" pitch prop.
The motor is mounted all the down (on the transom), I'm turning about 4800 to 5000 RPM wide open
with some noticible slippage of the prop (cavitation). Actually, the paint and some of the aluminum has "boiled"
off possibly from ventilation.
That said, I'm changing props going to a "Hyrus". The choices are few for this motor and as follows:

12.5 X 9"
12.5 X 13"

I think the 9" pitch is too low pitch and the 13" may be a bit too high. I'm leaning toward the 13", I'm hoping
the slightly smaller diameter will raise the RPM's as well.

I'm also raising the motor so I can try to turn this prop at 5300 to 5400 RPM.

What do you all think?

Thank you..

 

[steelespike]

Erosion of paint and metal is cavitation you don't usually feel cavitation you feel ventilation.
The Hydrus should resist ventilation and give you better grip it will very likely load the motor more
so you definitely don't want to increase the pitch.
If your going to err do it on the low side.Because if you end up too high you shouldn't use it for an extended period.

 

[fhhuber]

Big boat and relatively small engine... you aren't going racing. go for the power prop, not the speed prop.

 

[pbxcomm]

Lower pitch will defeat the purpose, by Increasing cavitation/blow out and slow the boat down further.. I'm lucky to get 11 to 12 MPH with myself in the Pontoon as current setup, loaded with passengers and gear, I think I could out swim it. I really need to increase RPM's without dropping pitch, so I will need to get creative.
I'm thinking slightly smaller diameter (12.5 X 11) and raising the motor one hole (one inch).

 

[steelespike]

You don't feel cavitation and it doesn't affect blow out. You feel ventilation Smaller diameter goes against pontoon prop theory larger diameter is usually suggested
for pontoons and other heard to push boats You already say you have ventilation(slippage) you need a prop,with more grip.
By the way (Slip) is a term that is used to define a props actual movement through the water. Ventilation is a better term for your slippage.
Increasing a props (rpm) should improve slip reduce ventilation. Reducing pitch may be accompanied by an increase in diameter which
should fight ventilation. Let us know how you make out.

 

[Sea Rider]

Can you plane that combo right now while lightly loaded ? That's right after passing fast displacement speed on flat calm no windy water cond..

Happy Boating