RPM question on 150 Optimax on 24ft. Manitou.

[trout74]

Facts:
24ft. Manitou Tritoon VP hull
150 HP Mercury Optimax PRO XS ( 2014)
Mirage Plus 15P Prop.
5.5 Hours on the Motor

Situation:
I have carefully watched RPM's and ran it from 2800 -4500 RPM's with short bursts of WOT. Also pulled kids on tube in that RPM range.

Max RPM's I can get is 5000 RPM's and that is playing with the trim with just me and Wife and no gear on board.
With me and the Wife and my 4 kids ( ages 2-10 ) my Max RPMs today was 4750RPM's. Full cooler, gear etc. Remember these kids are little, biggest one weighs 90 pds, and the rest are squirts still.

I called Mercury and they verified to me that the computer logs time spent between 2800 and 4500 RPM's and double oils for 120 minutes that the motor is in those RPM ranges. Any idling and WOT, it does not double oil and does not go towards the 120 minutes. Once the 120 minutes is up, the engine should gain 300 RPM's or more and stop the double oiling. He said it will be like a light switch once the 120 minutes is surpassed.

I have been very careful to be running in the RPM range of 2800-4500. The engine timer shows 5.5 hours after 2 hours of engine time on the water today with the family. I find it inconceivable that I haven't passed the 120 minute mark yet. Yet I haven't had the " light switch " moment yet.

Shouldn't a 150 HP Optimax be able to spin a 15P on a 24 ft. boat?
I know I could go to a 13P but that theoretically would only take me to 5300RPM with just me on the boat, so then going by the math you would go to an 11P for 5600 RPM's, and that seems too low for a 150HP on a pontoon boat.

Its possible I'm still in the computer controlled break-in, but I don't know how I could be.

Any thoughts by anyone here?

Thanks for reading long post,

Graham

 

[The Rooster]

Graham, the prop pitch should be about right. You should be able to get 5700-5800 rpms where the motor is rated for. Just sounds like the motor is sitting too low in the water. The cavitation plate should be right at the surface of the water while running. I've had 3 Optimax motors and never recall a "light switch" going off after break-in and gaining additional rpms. Good luck !!!

 

[trout74]

Hey thanks! so I checked that today while running with the motor trimmed all the way down, the plate the one above the prop was below the water line, don't know by how much, maybe 2-5 inches. so if the motor is trimmed all the way down, should it still be at the water line? and if so, ill raise it. The motor is set on the lowest setting, I have 5 total mounting holes, so I could raise it up to four more holes. should I go 2 holes? Ill have to take to dealer to do it, I don't have a cherry picker.

thanks for reply, FYI kids got going so fast on tube that they flipped it for the first time, wasn't possible on old boat. They thought flipping was so fun, made my wife nervous!
Look at the smiles! beached to play. My son caught a fish! However it was already dead!

 

[trout74]

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Tried to attach these to last post but this new system is not working properly, or I'm not doing it correctly.

smiles on the tube, beached having lunch and my boy found dead fish and continued to kill it further ( boys! )

 

[trout74]

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[The Rooster]

Hard to say how much to raise the motor. If you were able to do it yourself, I'd say try "1" hole at a time. Kind of seems like the dealer hasn't had a lot of experience outfitting high performance tri-toons. The way my dealer usually sets up tri- toons is by trimming the motor all the way down, and adjusting motor height until he can hit max. rpm's or very close w/ the boat mty and just himself onboard. Then w/ passengers , gear and a full tank of gas, you can trim the motor up some and should be able to achieve similar rpms, albiet at a somewhat slower speed. Hope that helps. I would definetly try this before playing w/ props. Good luck !!!

 

[trout74]

Yes,. I called Manitou and they confirmed that with a 20inch shaft, the motor should be mounted in the lowest position, which it is, duet the different size toons underneath. They also confirmed like you said that the 15P is correct prop. So they had me check the back of the Tachometer to make sure that the dial was set to position " 6". I checked that and indeed it was set to 6, ruling out an instrument installation error. Finally I called Mercury again, and they said it should get 5700 RPM's with a 15P prop. and to take to my dealer and they will run some tests. SOOO, tomorrow I will be driving to the dealer and drop it off, I'm sure they will get it squared away. Ill keep you posted. Thanks,
Graham

 

[craigmack]

For comparison, our 2012 Sylvan 8522 (just under 24') RPT tri-toon with a 2012 Mercury 150HP Fourstroke turning a 15P Enertia prop gets to 5200 RPM @ 36 MPH with 30 gals of gas and approx. 600 lbs of people and gear

 

[lakegeorge]

I have the 150 4 stroke also, like Craigmack and only get 5200 rpm's at 33mph. I have the Enertia 15 1/8 x 14 the dealer tried 4 props and different motor heights and they all ran 5200 or 5250 rpm's at 33 mph.

I should have bought a Yamaha as I'm disappointed with the performance of my motor.

 

[trout74]

Thanks for the comparisons, that helps. I actually went to the lake this weekend got the boat from the dealers lot, he hasn't gotten to it yet, and took the whole family. Four young kids, me and the wife and grandma and grandpa, fishing gear and coolers, pretty heavy I'm sure. But we maxed out at 4700 RPM's with a mirage plus 15P prop and clocked 33.2 MPH on the gps. Then the grandparents took the 2 yr. old home and it was just the 5 of us and I could get 33.8 MPH. regardless, I'm still 1000 RPMs short and would be happy if I got 600-800 more, I'm sure I would be close to 36 MPH. honestly I don't think ill have that much more fun with the added 3 MPH, but I would like to have the full RPM's. On a side note, I am very happy with my motor other than the max PRM's, that I'm sure will be resolved. I have put 50 gallons of fuel through it at 7.2 hours on the motor and my initial oil tank is still not empty, though almost. Very efficient! I think the motor sounds awesome and is not loud at all. The hole shot is great, it just needs to ring out a few more RPM's. ill update once I get it back from the dealer this week. On another side note I called and asked him about the Inertia prop, and perhaps we should try it. I told him I have been reading around and maybe it would fix the problem, and he said. " trust me, you have been reading too much, I have been in the boating business for 20 years, I have tested every prop and every motor, I have BRP Evinrude coming here every year trying to get me to switch from Mercury to Evinrude. I know the Mercury to better than the Evinrude and I know this is the right prop. I will make sure your get your PRM's, don't worry" so I will trust him for now. I have nothing to loose but time. and he has been fair and honest with me, and I like the guy. I have no reason not to trust him.

 

[trout74]

Update: Dealer said my tach is bad, new one on order. Said the motor is putting out full RPM's. That's good I guess, said motor is still in break in period too, according to the computer that they hook it up to. Since my tach was reading low, I was not running in the double oil period as long as I though I was. Easy fix. I feel better.

 

[The Rooster]

Excellent Graham. Sounds like they are on top of it. Now go terrorize some unsuspecting bowrider !!! :happy: