Pontoon Boat & Deck Boat Forum

Hey all, I've got a 2015 JC Neptoon 23tt with a Honda 150.
When I bought it, the old prop was beat up so I bought a new Quicksilver 15.25x15 aluminum prop as starting point and had nothing but issues with it blowing out. If I keep the motor trimmed all the way down it did fine but once I'm up and running, if I trimmed up more than 1/8 to 1/4 it just loses bit.
Motor was at 2nd hole down from top so I dropped it down one more hole to lowest spot and still the same issue.
It was running about 5600rpms at 32mph (gps) w/ just me and about 20 gallons of gas.

Ran a bunch of prop calculators and reviewed what others were using and it kept showing either a 15 or 17 pitch prop.

Decided to try a new stainless prop and picked up the Turning Point Express Mach3 14.25x17.
This one seemed to have better bit as I could trim up to about 1/2 before losing grip.
New rpm is about 6,000 trimmed down and about 6,200 trimmed up before losing grip. Speed was showing about 30 on the speedo.

Based on the new prop, it seems I should need a 19p prop to get the rpms down since the motor rpm range is 5000-6000. This just seems like a lot of pitch and the whole cavitation issue is driving me nuts.

These are the old pics I have after lowering it but when it was on the trailer and level, the cavitation plate was still about an inch higher than the bottom of the middle toon.

Not apples to apples but the standard prop Yamaha uses on a 150hp or 200hp inline 4 on a tritoon is a 14.5 x 15. That's what my F200 runs and it hits 6k on the nose at about 45mph, no blowout, and very responsive to trim. My boat is a G3 which is owned by Yamaha so it's a "power matched" setup. Cavitation plate is about 4" above the bottom of the outer toons.

Thanks, everything I've been reading people were saying that you get blow out if the cavitation plate is higher than the bottom of the toons?
Also a 15p prop should be the right one but based on the 17p I just tried, a 15 would run too high of rpm unless a 15+ bigger diameter prop is big enough to cut down on the rpms?

I'd really like to stay w/ aluminum due to running on a river that can get low fairly often. I somehow manage to always hit something at least once a year. Doesn't hurt so bad replacing a $100+ prop vs a $300+ .
I tried the stainless just because they are supposed to have more cupping to get some extra grip.

I think the major problem is the cavitation plate is above the center ‘toon. You need a longer/deeper shaft-length/prop-depth.
That prop, at speed, is up at the surface behind that center ‘toon.

That what I was/am thinking too but Woody another member here had basically the same boat (but w/ a Honda 135) w/ the same issue. He said he managed to get it working by adjusting the engine height (guessing lowered all the way) and going w/ a Stainless 15p prop.
That's also why I tried a stainless to get more bite.

Right now there is no way for me to get the motor any lower. I can't seem to find what it would take to make this long shaft into an extra-long shaft.

I was looking into jack plates but none of them will lower the engine any further, they are only designed to raise.

I did find this static jack plate and was thinking about trying to flip it around?
https://www.wholesalemarine.com/t-h-mar ... gJk_fD_BwE

The transom on the above boat appears to be non-typical in design at least in the photos as provided. As it is now it appears that the water is coming in under the boat and the smooth transitional flow to and through the prop is being spoiled by transom design issues that are creating problems.

Bamby wrote: ↑

Mon Jun 01, 2020 1:06 pm

The transom on the above boat appears to be non-typical in design at least in the photos as provided. As it is now it appears that the water is coming in under the boat and the smooth transitional flow to and through the prop is being spoiled by transom design issues that are creating problems.

I agree. I think that's a JC brand because they use those U shaped toons. But I'd be willing to bet that wasn't the original motor. I don't see any way to get that motor down low enough to get the cav plate where it should be. I'm guessing the original motor was either a long shaft, or perhaps the boat was built for an electric motor.