Water Pouring Over Transom at WOT

[Cleonard]

Hey all, new member here. Hoping to see if I can get some helpful info. I have a 4.5m Saturn Triton with a 40HP Johnson (I know it’s a little overkill, but really nice in the bigger waves). It’s sitting on a 6 inch setback jackplate, and I’ve fiddled enough with the height to know that I’m set at pretty darn close to the perfect height.

The issue I’m having is at WOT I’m basically getting a waterfall kicking back over the transom.

I’ve changed the trim pins up and down but really the only difference I’m seeing is cavitation on hard turns when it’s trimmed higher, and a low bow when it’s trimmed lower. Meaning the trim isn’t changing the issue at WOT. Any help would be appreciated.

[ptm]

To be honest- I think you have too much power- especially if you are running at WOT. Your transom will not be particularly high anyway for a relatively weighty engine, and I’m guessing the boat doesn’t have much of a ‘v’ hull, therefore not sending much water down the sides. Peg back your speed and things ought to settle down a bit.

[Matt]

6" setback on a 4M hull? So I assume this is almost certainly a "top speed" setup for lake & river use? That's not how I would expect a good "all round" setup on a 4M boat to be.

I used to run a 4M RIB with a 35 on the back and as I moved the CG back it did go faster just 1-up - it was good fun - but load carrying and acceleration were both affected negatively.

Anyway, regardless of that, you might well need a horizontal plate on the bottom of the jack plate to deflect the water fountain. My old race boat had an extra plate bolted to the bottom of it to prevent this - otherwise there used to be a water fountain coming up the middle of the jack plate - I assume this is where the water is coming? Probably something like a bit of 14-16 swg NS4 with a fold (up?) along both sides to stiffen it up, as long as it's securely mounted.

You can't quite see the plate here - but you can see the bolts that attached it, highlighted in red.