Prop Suggestion: '98 150 Optimax

[NFA]

Right now I have a 14 1/4 x 17 stock prop on it and I'm topping out at 5300RPM at WOT, approx. 43mp/h. From what I understand, this engine should be spinning a bit more, around the 55-5700RPM range.

What size/pitch prop would I need in order to bump up my RPMs a bit higher?

The engine is on an 18' Maxum Bowrider, approx. 2200lbs, give or take. Performs great, just wondering if I can get a few more revs out of it.

Thanks!



Scott

 

[Barnacle_Bill]

Re: Prop Suggestion: '98 150 Optimax

A 15" pitch would put you at 5700.

 

[hwsiii]

Re: Prop Suggestion: '98 150 Optimax

NFA, it actually ought to change it to 5,800 RPM, doing the math, if you stay with the same model of prop and Diameter as well. But it always helps to know the year, make and model of the engine we are talking about, as well as the gear ratio of the motor.


H

 

[NFA]

Re: Prop Suggestion: '98 150 Optimax

It's in the subject of the post.

1998, 150 Optimax.

Don't know the gear ration.

With a 15 pitch, does that make it a 15 x 17 or a 14 1/4 x 15?

Thanks for the replies.


SSS

 

[hwsiii]

Re: Prop Suggestion: '98 150 Optimax

Sorry about that, I don't pay much attention to the headings. Since I know that, I find that you have a 1.87 gear ratio and 5600 WOT RPM. Knowing that I can tell you to change to a 14.25 x 16" prop in the same model and you will be turning almost exactly 5600 RPM, which is what Mercury said is the maximum RPM for that motor. Here are the numbers.

And here is your Slip factor now, this is a very low Slip.

H

 

[NFA]

Re: Prop Suggestion: '98 150 Optimax

Thanks bud, appreciate it. I don't plan on keeping it wide open for an extended period of time at all, but I'll sleep better knowing that I have that option and that the engine is running with the proper prop.

If I go with a stainless steel, would that be the same pitch and diameter, etc? Just in stainless?

Thanks!



SSS

 

[hwsiii]

Re: Prop Suggestion: '98 150 Optimax

A lot of the times going with a stainless steel prop creates a whole new set of criteria. If you really want one let me know and we will figure out which is the best one for your boat and motor.

H

 

[NFA]

Re: Prop Suggestion: '98 150 Optimax

Thanks H, I'll keep you posted.



SSS

 

[hwsiii]

Re: Prop Suggestion: '98 150 Optimax

Thank you, I would appreciate it very much.

H

 

[NFA]

Re: Prop Suggestion: '98 150 Optimax

I was just going through the posts and found this one from a couple years ago.

Since this post, I've been looking at different props. I've tried 6 different ones and have narrowed it down to either a 14.25x21 - 23 pitch, or a 13.75x21 - 23, stainless steel.

After testing out all six props, I kept a 13.75x25 SS on and it bumped up my speed by about 10MPH. unfortunately though the revs weren't up to where they should be at WOT. I was capping out at about 4800RPM, but I should be around the 5200-5500RPM range. Currently though I'm in the middle of dropping pitch down to either 21 or 23 with the hopes of getting the RPMs up to where they should be at WOT. Right now I've got a 13.7x21 SS Raker mounted, but just waiting on the next nice day to get out and test it.

Will post my results, and if anyone here has any advice, or things to look for, or thoughts on different sizes of props to test out, let me know.

Just as a reminder, it's an 18' Maxum bowrider, 150 Merc Optimax, approx. weight of 2600lbs fully loaded. I use the boat mostly for cruising with a bit of skiing and wakeboarding.

With the new prop I'm hoping to bump up the speed and overall performance of the engine and boat.

Thanks everyone;


Scott