RPMs Don't Seem Right?

[jwelch16]

All - new owner of a 2010 22 Ft Shoalwater Legend (V Tunnel) with 150 Optimax. Interested in good all around performance, with focus on holeshot and planing in shallow water. Just outfitted and propped out with a Stilletto 4 Blade Stainless prop 21 pitch. Working through break-in procedures and could only achieve 4,000 RPM tops today - speed was 34 knots. Hull weight is 1650 lbs. Thinking I should have a better RPM top end / speed - any observations welcome.

 

[Bifflefan]

Re: RPMs Don't Seem Right?

That 4 blade 21p is like a 3 blade 22p.
Possible to much prop "p" for the combo.

 

[Dhadley]

Re: RPMs Don't Seem Right?

With that combo we use a 19 a 3 blade Stiletto or a 17 4 blade so you're close prop-wise. However, at only 4000 rpm we may have more issues. Let's verify that the motor is running right. You're looking for 1500-1800 rpm which is probably more than a simple prop change.

 

[jwelch16]

Re: RPMs Don't Seem Right?

Thanks for the replies so far. I'm taking the boat back to the shop that did the outfitting - I may have a little too much "blade" for the boat / engine to turn efficiently -- will look to optimize that over the next couple of weeks and post results on the forum. Also a bit concerned that water pressure reading wasn't quite what I expected - never above 10 PSI - even at full throttle.

Brand new 150 Optimax - expected to see that number between 12 - 15 -- disappointed in the amount (or lack of) information available in the owners manual(s).

 

[Dhadley]

Re: RPMs Don't Seem Right?

Something isn't right with the pressure gauge or where it's hooked up. If you really had less than 10 lbs of water pressure at wot you'd be talking about warning horns or possibly how well the warranty works.

 

[Legend22]

Re: RPMs Don't Seem Right?

I have a custom 15P 4blade from Mike Hood in Houston, TX and it's a great prop. It turns right at 5700RPM and my top end is mid 30's max. I was more interested in shallow water performance than speed and this thing hooks up all the time. I also have a stock Mercury prop 14.25 X 17P 3blade that will run a little over my range and will run me about 40MPH. I may have Mike cup it and it should make a great back up.
Please have your mechanic check the shifter cables. Mine was wired in reverse and I had the same issue with low RPM's. It was a mess......if they tell you that your motor is a counter rotating model, call Mercury right away to verify.