Why is my new prop worse than my old?

[TRAILN]

I bought a used boat this summer and it had a very chewed up aluminum prop. I replaced it with a brand new prop with the same specs and now I get less RPM and less speed.

'86 Johnson 60HP. 13 1/4 x 17" Pitch. Both aluminum, both same size and pitch.

old prop 35 mph / 5600 RPM
new prop 31 mph / 5000 rpm

Any ideas why?

 

[SparkieBoat]

Re: Why is my new prop worse than my old?

props from different manufacturers are different. and give different results, as you can see. that is why.

 

[willamettejeff]

Re: Why is my new prop worse than my old?

New prop is cupped and old one is not perhaps. If the trailing edge of the blades has a sharp curve upward then the prop is cupped. This essentially adds about 2 inches to the pitch making your new 17 really a 19. Would need to go to a 15 pitch cupped to get relatively the same performance of a 17 uncupped.

-- Jeff

 

[steelespike]

Re: Why is my new prop worse than my old?

Different props will produce differemt rersults and the kicker is your original was chewed up.
Depending on the size and weight of your boat a 17 seems a little large.
Maybe you should get your old prop repaired and give it a try.
35 is a pretty good speed.

 

[cmjust0]

Re: Why is my new prop worse than my old?

Depending on the size and weight of your boat a 17 seems a little large.

I'm by no means a prop expert, but I was thinking the same thing.. I have a 70hp w/ a cupped 15 pitch stainless on a 15.5' fiberglass bass boat and it's a bit much, especially coming out of the hole with anything other than me, a pop and a sandwich.. Add a full grown passenger and I'm pretty sure you could eat the sandwich and drink the pop in the time it takes to plane out...lol

And that's 10 more horses and 2" less pitch than what you're running, though I have no clue what kind of boat you're talking about.

I actually swapped mine out for the aluminum 15 pitch that also came with the boat, but I've yet to run it. Something tells me it's going to perform better, though.. I think the previous owner just wanted a stainless prop because they're sexier...lol

 

[sschefer]

Re: Why is my new prop worse than my old?

13 x 17 on a 60hp motor??? What are you pushing a 14' skiff?????? That's over prop'd and the chewed up prop was probably acting more like a 11 x 15. I run a 10 x 13 on my 60 pushing a 16' 1800lb heavy gauge aluminum boat. I hit 32 at 6200 Max RPM and that's a perfect setup.

LMAO... we all must think and post at the same time.... General concensous is ..... Too much prop...

 

[TRAILN]

Re: Why is my new prop worse than my old?

Thanks all,
So if I understand this correctly, if I switch from a 17" to 15" pitch I will gain my RPM and speed back?

 

[ufm82]

Re: Why is my new prop worse than my old?

You should- the chewed up prop had a lot of slip due to the blade damage. That allowed more RPM and that gave you a little more speed. When you went to a new prop that got a better bite you dropped RPM and thus some speed. However, I agree with the pitch remark- too much for a 60 hp. Drop to the 15 and you should see your RPMs back up where they should be andf your speed should be OK.

 

[TRAILN]

Re: Why is my new prop worse than my old?

Got it, thanks!
Anyone wants to buy a slightly used 17" prop let me know

 

[cmjust0]

Re: Why is my new prop worse than my old?

Anyone wants to buy a slightly used 17" prop let me know

Haha! I got a chuckle out of this.. Well played, sir.. Well played..