Best Prop pitch??

[jddens]

I have a 1985 Bayliner Trophy 17 foot bass boat with the Force 85hp engine. What is the optimum prop pitch for max cruising speed? I usually boat alone and don't pull tubes or skiers so hole shot is not important to me, just optimum cruising speed. Had a prop I liked but damaged it and can't find ANY numbers on it....put on my 21 pitch spare and top end dropped significantly so I'm guessing maybe 17-19 pitch?? Thanks in advance for any information............John

 

[Bustedknuckle84]

Re: Best Prop pitch??

check in the prop section forum man this will more then likely get moved anyways though.

 

[pnwboat]

Re: Best Prop pitch??

You really need a tach to see engine RPM, combined with speed to determine best prop pitch. Your guess of 17 - 19 pitch is probably in the ball park from past experience.

 

[steelespike]

Re: Best Prop pitch??

Did you look under the prop nut for some numbers?A prop shop can measure it for you.
For the health of your motor you need some rpm figures.A tinytach is about $50 and easy to install.With speed ,prop size and rpm you can really fine tune the setup.

 

[jerryjerry05]

Re: Best Prop pitch??

Someplace on that prop is a number.Stamped in the side or end.It could be a faint 17 or 19 on the side.It might be on the end where the nut is.
That boat came with a 17 or 19.
If you can't find a number.Take it to a dealer who can send it out to rebuild.They can identify what size it is.
Like PN and Steel says a tach is a GOOD thing on a boat.It will give an idea what your running and get proper performance.
Too much prop costs more $ to run, too little no speed.
Look at the prop and post your findings.J

 

[Frank Acampora]

Re: Best Prop pitch??

On that year engine USUALLY the prop pitch would be stamped between two of the blades on the hub IF it was a stock prop. For example: It would be something like 310-19 indicating a stainless prop of 19 pitch. These numbers were also stamped into the hub under the prop nut and washer. Sometimes they are difficult to see because "working " of the nut and washer tends to wear the aluminum.

Right off the bat, even without RPM figures, I can tell you that a 21 pitch prop is way too much for that engine on a 17 foot hull. RPM will drop drastically and top speed will be down.

That engine was not a particularly strong one and doesn't have the torque to turn a 21 pitch prop. While 19 pitch MIGHT do it, more than likely you should be using a 17 pitch. Of course, the only sure way to tell is by tachometer. The engine should be running at or near 5500 RPM at full throttle.

If I only had a choice of one gauge on my boat, it would be the tach. It tells you the most about your engine .

 

[jddens]

Re: Best Prop pitch??

Thanks for the reply's.....OK, I found some numbers on the hub end, says "Michigan 072107...I think, kinda hard to read. I have a couple small tachs from V8 cars, will they work? If not, where do I get a tach for a 3cyl? Thanks!! John

 

[jerryjerry05]

Re: Best Prop pitch??

Auto tachs won't usually work.They sell an item called a Tiny Tach.Just follow the directions and it installs in minutes.You can get on line or at any Mercury dealer.
Send Michigan Wheel an e-mail with the numbers you have they will tell you what it is.And how much for a new prop.They sell props here.Call them with the #s and they can help too.J

 

[Cannondale]

Re: Best Prop pitch??

If that number is correct, your current prop is a 13 1/4 x 17P.

 

[jddens]

Re: Best Prop pitch??

I double checked the numbers and they are good. Thanks for all the info. I found a local prop shop, I'll take it to them and see what they can do........I'll also look for the tiny tach.............Thanks again.............John