Prop Sizing

J

jharcus

Recruit
Joined
Sep 27, 2006
Messages
3
I have a 16 Ft Glastron GS 160 with a 1996 Johnson 115 2 stroke with powertrim. I run a 17 pitch 14 inch 3 blade alum prop. It has great hole shot but I can over rev it by 300 rpm at WOT. I use this boat to ski my family so the holeshot is great but I also use it to cruise down the river and constantly watching the tach is a pain. Would I be better off with a 18 pitch 4 blade SS or a 19 pitch 3 blade SS to end this problem. Also would there be a noticable loss of acceleration when sking with a prop change.
 
C

Crownie2

Petty Officer 1st Class
Joined
Jul 26, 2006
Messages
378
Re: Prop Sizing

If you are sure your tach is correct, I'd try a 17" SS three blade prop. This should bring the RPM's down by at least 100 and shouldn't effect your holeshot.

Of course a 19" would bring the RPM's down more, but will more than likely hurt the holeshot.

I would think you could tell by the sound of the engine about where it is running and wouldn't need to look at the tach so much, once you have reached the speed you want.

Bob
 
W

walleyehed

Admiral
Joined
Jun 29, 2003
Messages
6,767
Re: Prop Sizing

Is your 115 a crossflow or is it a Looper (vents in hood, 60 deg. narrow powerhead).
300 over what RPM with which engine.
I don't think you are truely over-reving if you are turning 5800, and if you'l specify which engine you have, I'll tell ya why.
 
J

jharcus

Recruit
Joined
Sep 27, 2006
Messages
3
Re: Prop Sizing

Thanks for your reply. My 115 Johnson is a crossflow and the manual calls 5500 as max rpm. Also if you could suggest a make of SS prop that you or other boaters have had good performance from I would appreciate it .
 
W

walleyehed

Admiral
Joined
Jun 29, 2003
Messages
6,767
Re: Prop Sizing

Your 1996 X-Flow needs to be propped for 5800RPM with a normal load.
The reason for this is the quality of gas that was available 10 yrs ago when the engine was built, and the crap fuel we get today.
Combustion temps are higher with the newer fuels, so we find they last longer if we relieve some of the stress by increasing the RPM by about 3-400 on the X-Flow.
As for Props..I guess I know a little bit about some of them. I think if you were to install a Stiletto 21317, you'll see a good improvement over-all.
 
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