Prop size and pitch

[Morris31607]

Good afternoon, have a 17 foot sylvan I purchased for a decent price it has a 1981 Johnson 50 on it the prop was okay until I hit a rock, the only thing is the boat would not get on plane when you open throttle to wot it would just stick nose in the air and mad speed was 13mph on GPS with 2 guys and fishing equip. Just wondering if some one can recommend a prop that will get me on plane not to worried about speed but when trying to get from point a to point b its hard when you can't see over the front. Any suggestions greatly appreciated

 

[anonOmattie]

trim the motor down? or add an hydrofoil?

 

[ThomW]

What did you have on for a prop before? Pitch? What were your WOT rpm's at, or around?

 

[Sea Rider]

If he could plane combo before hitting rock assume hard, prop hub is kaputt. Need to do a hub slip test to check if serviceable or not. Trimming OB down will literally bury nose down into sea, bad way to go..

Happy Boating

 

[Morris31607]

Sorry guys since I have owned the boat it would not plane out before I hit the rock believe prop was 9x13 just lolling for suggestion to get it too plane if I purchasea new prop, wot was 4800 rpm jyst felt real sluggish And as if I was towing something betting me

 

[Morris31607]

Also added hydrofoil

 

[Sea Rider]

Did combo plane with hydrofoil ? nope, right ? What's the factory stated mi-max wot rpm range for that OB, need to know that. If range is 5000-5500 rpm, at 4800 OB is at the lugging side, if range is 5500-6000 much worse. Need to dial a prop for OB to rev around middle rpm, but full wot rpm is preferred as usually loaded. How much less pitch ? will depend entirely on the wot range for that 50 horse..

Happy Boating

 

[jimmbo]

The 1981 50Hp had a WOT range of 4500 - 5500 rpm
A 17ft with a 50HP is not going to be a speed demon by any means, nor jump on plane instantly.
A prop for that engine is not going to have a 9 inch Diameter, more like 11 1/4 thru 12 1/2 inches
The 81 OMC Prop Charts show a 12 1/2 X 13 prop for 15 - 18ft boats and a speed range of 20 - 28 mph. If that is your 13 inch prop, you would be at the higher end for boat size and thus at the lower end of the RPM range. The lowest pitch offered by OMC back then was an 11 inch