Best prop for a 24ft pontoon with a 3.0 Mercruiser

98fatboy

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Jun 22, 2017
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First post, here are the specs that I have
1994 Harris flotebote 240 classic
3.0L Mercruiser
Currently has a solas 14.25 17 p 3 blade
The problem I am having is blow out/ cavitation around 3000 rpms. This is while pulling a tube with 4 people on boat and 2 on the tube. With just me and the wife 3400 rpms I get the same issue. Changed out prop with a loaner solas 15/15 same issue at 4000 rpm and gps speed 19.7 mph. What would be the best prop to eliminate the slipping clutch feeling and increase boat speed?
 

Scott Danforth

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if you had an outboard, I would say, lower the motor.

since you have an I/O in the pontoon, I suggest trimming down a bit more and moving some of the weight from the bow to the stern.

where is your trim set to? you should have it near all the way down

what is your WOT RPM?
 

alldodge

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Normally it doesn't help to trim a pontoon up much at all. What happens if you keep in full down?
 

98fatboy

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All of this is happening with trim all the way down, 3.0 mercruiser should top out between 4600-4800, best I could get was with the 15-15p @4200 and 19mph. I even checked to see if the foot was loosing trim, foot is all the way down. as far as weight goes, it acts the same no matter where I put the weight. I've had all my kids on the back (5kids) biggest kid is 240lb along with the cooler.
 

alldodge

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Suggest pulling the Toon out and then take a pic and post of the rear of the boat focusing on the motor Cav plate and the Toon bottom

Also need to post one more time with anything, because you need to post three times before you can upload pics
 

Scott Danforth

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when running the anti-cav plate should be about 1-2" below the water line.

with 5 people in the back, you may be aft heavy. have you moved everyone to the front and tried that?
 

98fatboy

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I have moved everyone around on the ol toon trying to see if it was a weight issue. I will try to get some pictures, dealing with Cindy and the aftermath now.
 

98fatboy

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Still no pics yet, I did check everything under the ol toon, everything is where it is supposed to be, nothing hanging down interfering with stern drive. New development, got a 15in 15p 4 blade prop,(not sure of manufacturer) ran like crap. Was worse than with the original prop. Does anyone have the same or similar boat/motor set up? If so what prop do you run? What kind of specs are you getting? Is there a such thing as a pontoon boat specific prop? It was a used prop, probably the reason for getting rid of it
 

alldodge

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New development, got a 15in 15p 4 blade prop,(not sure of manufacturer) ran like crap. Was worse than with the original prop.

A 15 pitch 4-blade is like a 17 pitch 3-blade except it takes more power to turn the prop. So it being worst then the 17-3 would be expected
 

98fatboy

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Just spoke with a friend's dad, he has similar toon with a black max 15 1/2 15p running 34mph on a gps, only difference is his toon is 2 years newer than mine. Is there much difference in an ob prop and an i/o prop? The 15/15 I borrowed was off an ob.
 

98fatboy

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Update...... Bought a Merc 15 1/2x15p prop. Torque flo II hub kit. Just got back from installing all brand new components. The verdict? All the exact same issues I have had to begin with. Had a buddy with me this time, now I believe I have a bad coupler. This is a 1994 Harris flotebote 240 classic 3.0L mercruiser. Any ideas on how hard it will be to replace myself? Seeing how this will be my first go at it, was looking for any feedback.
 

alldodge

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The hardest part about changing the coupler is pulling the motor. Once pulled its just removing the bell housing then the coupler.

Suggest pulling the drive and look at the coupler thru the gimbal
 

98fatboy

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What I was apparently calling blow out was actually the coupler slipping causing the feeling of a slipping clutch. When I had someone with me to visually watch the prop and foot there was no change in water characteristics, just engine revving with a loss of speed.
 

98fatboy

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I am planning on pulling it out of the water in the next couple of weeks. Time is not my friend at the moment. Just hoping it will last through the weekend for this birthday weekend.
 

Maclin

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Usually once a coupler slips that is it, as it is all metal to metal and the splines are gone. A spun prop hub can allow some torque to pass on to the prop, but usually once it has spun it will never be able to take full power without spinning more and more.
 

98fatboy

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Well I am out on the toon now, 6 kids 2 adults, boat pulls tube fine through 3200 rpms, just over that it acts like it blows out, rpms rev up boat slows down. Back out of throttle then get back in it pulls fine to 3200. Steady throttle at 3000 does fine unless I try to turn sharp, then rpms shoot up speed drops. No noise, no burnt rubber smell. Ohh this is a brand new prop, and hub.
 

muskyfins

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I don't think your problem is prop. I have seen coupler issues where you could get 1500-2000 rpm out of it before it would slip. But 3200 seems high for that. Certainly worth a look.
 

98fatboy

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Going to pick up a new hub in the morning, it's cheaper than a coupler and faster to swap out. Worse case scenario, I have an extra hub.
 

98fatboy

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Brand new hub kit, brand new Quicksilver 15 1/2?15p prop. Pulled strong got to 4000 rpm wot 20mph on a GPS, just a little bit of a wake/rough water and rpms shoot up and boat slows down. Couple of guys said put a wide aluminum whale tail on it? Was also told to drop to a 13p prop. At this point I'm almost ready to pull the boat out and completely go through the boat and replace every little bearing, seal, coupler, mount, and hell, may even rebuild the engine while I'm at it. I just hate throwing parts at something and guessing that this time it might fix it.
 
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