prop pitch

[josh333]

hey i got a 1988 bayliner maxum ski boat. it has a mercury force 125hp. i still have the stock propeller on it but it is getting pretty worn out. i would like to no if going to a 17" pitch would make my top speed be a little faster. i am going about 34mph at 5000rpm. thanks for your help

josh

 

[steelespike]

Re: prop pitch

welcome.There really isn't a standard prop, usually would end up based on typical load and activities.
Is the Force an 88 also? What is the present prop? Numbers should appear near the base of the blades.
What size is the boat? Is it a Bayliner or a Maxum?
I don't think there is a Bayliner Maxum.

 

[josh333]

Re: prop pitch

Yes the motor is an 88. There are no numbers on the prop at all! And on my registration it says bayliner. The side of the boat says maxum. Thanks!

 

[shrew]

Re: prop pitch

If the side of the boat says Maxum, it's a Maxum, not a Bayliner. They are both made by Brunswick, along with many other brands such as Searay, Cabo, Hatteras, Meridian, Lund....as well as Mercury and Mercruiser (and about 15 other boat brands). I believe that Brunswick bought Maxum somewhere in the mid 1990's, so it is doubtful that a '88 Maxum would be a Brunswick boat and they were ALWAYS seperate subsidiaries with distinct product lines and brand identities.

You might want to get yoru paperwork corrected.

 

[shrew]

Re: prop pitch

To address your question correctly. What is the range of RPM's for Wide Open Throtle (WOT) for that motor? When on plane and properly trimmed, what is the max RPM at WOT that you're actually achieving. We're assuming the motor is properly tuned, the boat hull is clean and the boat is not overloaded with weight.

Max. RPM is always a range. (e.g. 4000 - 4400 rpm for example). If you're within the range you're generally propped correctly. If you're under the range, you're typically over propped. If you'r over th range, then you're typically underpropped.

Going down in pitch will typically improve hole shots (shorten time to get on plane), but lower top end speed and increase RPM's at WOT

Going up in pitch will slow down hole shots, increase max speed's, but can decrease rpm at WOT.

Decide which you are trying to improve. Keeping in mind that if some is good, more is not necessarily better. You will only be able to vary so much one way or the other. Over revving or lugging a motor too much will hurt it. You can always watch the RPM's if underpropped and ensure you're operating within range, however overpropping will alays be straining the motor. Neither is really a good condition to be in.

Some of this might require some trial and error.