60hp Johnson on 16’ Aluminum boat prop recommendations

[eMKay]

I have a 1982 Starcraft SS 160 with a 1985 Johnson 60 (2 cyl, small gearcase), The current prop is 12.25 x 15p and I get 4500rpm max at 35mph with just me and 30 loaded with. It gets up on plane fine, pulls a tube fine, just not getting max RPM. I was thinking of changing to a 13p prop but was wondering if that would be detrimental since the boat performs just fine everywhere else. I cruise at 20-22 mph at 3500rpm, does changing to a 2” smaller pitch move RPM up 4-600rpm across the entire rev range, or is it only at WOT and is a scale depending on RPM? (Example, my 3500 cruise RPM is now 3700 and not over 4000?)

 

[ahicks]

Anything is possible, but I would expect to see the "scale, depending on rpm" scenario you describe.

What is the upper rpm limit for this engine?

 

[eMKay]

5000-6000rpm

 

[ahicks]

Sounds like you could drop a couple inches of pitch with no problem. OR-

If you have a good prop repair shop available (underline good) you could talk to them about what you have going on now, and what you'd like to see. If they're worth their salt, and aren't in it just to sell props, they may be able to work some magic on the prop you have to get it much closer to "perfect" for your purposes.

 

[jimmbo]

First I would find out if the tach is set correctly and is accurate. If it is and the engine is in good mechanical shape and in tune, with a 15" prop, it should be running in the lower end of the 5000 - 6000 range. A 13 would be a better choice as it should put you a bit above the 5500 mark. I say should, but either your tach is out, you have a performance issue with your engine, or your boat has several hundred pounds of dead weight aboard, as in water soaked floatation foam. Perhaps a combination of 2 or more issues

 

[eMKay]

The tach is new and set correctly, I stripped the boat to bare aluminum and rebuilt it so those two issues are solved.

https://forums.iboats.com/forum/boa...39820-not-another-starcraft-160ss-restoration

It will approach 5000 with just me in it and go 35mph, but I’m never going to be alone in this boat, there will always be at least 3 people in it. So it is always loaded. As for the engine, the last thing I have to do is a compression test which I will do as soon as I find my compression test gauge, I will try and get that done today. I’m pretty confident it’s healthy though

 

[ahicks]

If it's running 35mph, it's likely healthy enough.

 

[Sea Rider]

It's much better to dial a top prop that revs at full wot revs with min 2 up that solo boating, that way when with 3 up engine should rev at middle wot rpm range. All my water toys have maximized 3 blade alum props to run that way...

Happy Boating

 

[eMKay]

Thanks, compression is 135, and 140. I think I’ll try a 13 pitch prop and see what happens.