Could anyone recommend a size and pitch prop for a 70hp OMC on an old 24' pontoon?

[jbjennings]

1974 OMC 70hp outboard mounted on a standard Aloha pontoon boat (not a tritoon) with standard seats and 3/4" marine plywood decking on floor which is also probably standard.
I was hoping someone could recommend a prop for this setup.
I sure would appreciate it,
JBJennings

 

[SkiDad]

Re: Could anyone recommend a size and pitch prop for a 70hp OMC on an old 24' pontoon

edit: i have bad advice so I'm just taking it out

 

[jestor68]

Re: Could anyone recommend a size and pitch prop for a 70hp OMC on an old 24' pontoon

The Evinrude site has a couple of tests of their 75 on 22 ft pontoon boats and both a using a 11 pitch prop to turn 5400-5500 rpm.

Bear in mind that these engines tested are brand new.

It seems reasonable that your 70 might do OK with a 10 pitch prop, bearing in mind that the rpm can go as high as 6000 rpm on your 70.

 

[steelespike]

Re: Could anyone recommend a size and pitch prop for a 70hp OMC on an old 24' pontoon

jestor generally has these things nailed down pretty well.
I would only add that the 70 uses a 2.42 ratio while the 75 uses a 2.00.
Makes me think that assuming the 70 is sound an 11" would be closer to what you need.
Jestor, does that seem reasonable?

 

[jestor68]

Re: Could anyone recommend a size and pitch prop for a 70hp OMC on an old 24' pontoon

jestor generally has these things nailed down pretty well.
I would only add that the 70 uses a 2.42 ratio while the 75 uses a 2.00.
Makes me think that assuming the 70 is sound an 11" would be closer to what you need.
Jestor, does that seem reasonable?

With so many unknowns, the 10-11 pitch range seems reasonable.

 

[Bob_VT]

Re: Could anyone recommend a size and pitch prop for a 70hp OMC on an old 24' pontoon

What prop is on it right now? Is there a tach connected? Do you know the rpms that it was turning?

There are also 4 blade 13" props but, that will all depend on your present situation.

 

[dazk14]

Re: Could anyone recommend a size and pitch prop for a 70hp OMC on an old 24' pontoon

Without ANY speed data.

Michigan wheel make a 10" pitch 4 blade that would be in the hunt. I wouldn't go smaller and I'm not aware of an 11" or 12" 4 blade.

 

[Rkrough]

Re: Could anyone recommend a size and pitch prop for a 70hp OMC on an old 24' pontoon

The 11 pitch on a 70hp should be about right for a 24' pleasure 'toon. We had a 1985 70hp on a 22' pontoon workboat last year that we used to transport lumber on. We had an OMC 14 x 9 pitch on and it was perfect for maneuvering and towing, It would still make ~15 knots at 5500. We also installed a CDI power pack(113-2556) with a built-in 5800 rpm rev limiter to prevent over revving when the boat was unladen.