1985 Mecury 18hp Props

[Hammbone1971]

My 1985 Mecury 18hp has a really worn-out prop on it now.I have not ran this motor in the water yet since I just rebuilt most of the issues it had when I traded for it.I have it running ok at the time.Just no water time cause the prop is in bad shape.It has a 8 inch 13 pitch on it now...not sure it's the one that came on it.....Question is can I put a 9.5 pitch propeller on it? And what will it change.Oh the new prop is also 9.5" in size also.Will it work ok? Thanks for any advice!

 

[roscoe]

You can put anywhere from a 9pitch to a 15pitch prop on your motor.

Correct pitch is determined by the boat size and weight, and performance with the current prop.

For example, a 9 pitch prop will be better for a heavier boat, will get it on plane easier, will allow engine to run at faster rpm.
A 15 pitch prop would be better for a lighter boat, and will push the boat faster, but will slow the engine down.

The trick is to match the prop with the load it needs to move, and still maintain the ability of the engine to reach the designated rpm range for the engine.

So a few examples:
If you are pushing around a pontoon or pushing a sailboat out of the marina, you want a low pitch prop, like a 7 or 9 pitch.
Have a 16' fishing boat, then an 11 pitch might be right.
Flying around in a 12' hydroplane, you would want a 15 pitch.


So, your 9.5 pitch verses the 13 pitch, will allow the engine to rev higher, will give it more pushing power, will plane a boat easier.

 

[steelespike]

Welcome,Read the stickies at the top of the prop forum. Get us as much info as possible.A lightly loaded test run with the present prop unless it is completely out of the question, gps speed and the rpm will help.Pictures of the outfit also helps.
The motor needs to be able to operate near the top of the rpm rating.

 

[Sea Rider]

It's a wild guess, will need an induction tach to check wot speed with you alone on flat calm no wind waters, then will know if insdie min.max rpm factory stated parameters for that engine, once you know that can dial a particular p?tch size for your particular boating requirements to put you on the max or near max wot rpm safely.

Happy Boating

 

[Hammbone1971]

I'm already learning....Thanks yall!!