Propeller / Top End Speed ?

[charliegiggles]

Hi,

I have 70HP 1979 Mercury. I bought a new turning point prop. It has a 13 pitch. At full out with the boat loaded I'm turning at 5000 rpm and top speed is about 32Mph. The engine's proper rpm range is between 5000 and 5500 rpm at full throttle as per the manual.

I was wondering if I put a prop with less pitch "increase rpm" if I would achieve better top end speed or should I just leave things as is?

Thanks as usual....

 

[tashasdaddy]

Re: Propeller / Top End Speed ?

you need to get as close to 5500 as possible, speed is not the item, your are lugging the engine, being over propped, increasing wear. if you want more speed get more HP.

 

[charliegiggles]

Re: Propeller / Top End Speed ?

K thanks. I'll get a lower pitched prop. Should I go with 12 or 11 pitch based on my current 5k rpm 13 pitch?

 

[JB]

Re: Propeller / Top End Speed ?

Moved to the Prop Forum

 

[Dhadley]

Re: Propeller / Top End Speed ?

Reducing pitch to gain rpm is only a last resort. Most likely you'll lose efficiency. Experiment with the set up to gain rpm with the same prop. That will always increase efficiency.