What prop to buy?

[b.gagnon]

I have a 1978 17' Sea Nymph(Aluminium) boat with a 1979 70hp Chrysler outboard turning a 17p prop.<br />The boat will hit 34.6mph @ 5050rpm (with me and gear). The motor says 5100rpm max. I would like to buy a spare prop and was hoping I could turn a 19p for some extra speed. The boat as is, has a great hole shot an can still pull off 30-32mph with four people and gear.<br />How much rpm and speed could I gain by doing this?

 

[Silvertip]

Re: What prop to buy?

You will not gain RPM, you will lose RPM. Prop pitch changes are like changing gears in a car. A 19 pitch prop is higher (like a gear) than the 17. You will loose about 350 - 400 RPM with the 19 pitch. That means the engine will now be farther off its power peak (lugging)so you will likely lose speed as well, plus the hole shot will diminish. The prop you have is optimum. Stay with it.

 

[b.gagnon]

Re: What prop to buy?

WOT range is 4100-5100 so I should be able to loose a few rpm?

 

[stevens]

Re: What prop to buy?

No, I think you want to be at the top of the range, for both performance and longevity of the engine. Your best bet might be to find a more effective prop in the same (correct) pitch.

 

[walleyehed]

Re: What prop to buy?

Ditto what Stevens said...

 

[b.gagnon]

Re: What prop to buy?

This is a non hub exhaust. I have not found anything that would qualify as more effective. Everything I have seen looks to be a stock type prop. Any ideas where to find one?

 

[stevens]

Re: What prop to buy?

Don't know if this will help, but have you tried propellersonline.com ? They seem to have some Michigan Wheel props that might fit, at $125-130 or so.

 

[b.gagnon]

Re: What prop to buy?

Iboats has a new 19p for this motor that they are selling for 75$, They don't stock a 17. Could I really loose 400rpm?<br />How bad of an idea would this truely be?

 

[walleyehed]

Re: What prop to buy?

Lose 400RPM and gain fuel use in all areas of operation. Just changing props might gain a mile or 2 an hour, but expect more fuel use due to lower RPM at a given throttle setting..if it was running 5100-5200WOT the cruise RPM will have better fuel economy, your hole-shot will be better and when you have 4 in the boat, you won't be burning your engine up from high combustion temps.