alls good

[Cracker Larry]

I'm trying to find you a few pictures. Here is the first one, this is Aripeka's XF20 (before he painted it red) with my OD18 tied up next to it. You can see the anti ventilation plate on both of our engines are right at waterline level. Both are 70 Yamahas, both on jack plates. His is higher than mine, about even with the top of the tunnel. Maybe a little higher.

[Cracker Larry]

Look at these pictures, this is Red Alert before she was red. It's in front of my GF16 but you can see how high the engine is.



This is Brian's XF20



Both have almost twice the HP of your boat and both engines are mounted much higher than yours.

[jacquesmm]

From what I could see from the gallery pictures, the jackplate/engine mounting plate are scooping water into the boat when you lower the jackplate. I'm running a Powertech triple cup ,four blade prop and it doesn't cavitate.

That's how the water floods the boat.

[Noles309]

Nice looking boat
The transom looks low to me. It is straight across at gunnel level, not raised like the others shown. You might have to build it up to get a high enough mounting position for the JP/motor.

[Matt Gent]

My pontoon boat does the same thing when the engine is at low trim angles. Water shoots up the front of the tower housing onto the clamp, then fwd into the motor mount area. Luckily for me, that is still outside the boat so it just goes back into the river.

The pontoon may be similar to the tunnel in that my center pod is higher than the waterline at rest (just barely) and it is higher running than a standard flat or v-bottom would be. My cavitation plate is a few inches below the bottom of the motor pod; any higher and the engine loses cooling water under certain loading conditions.

On mine as I trim the motor up a bit (to around level relative to the water, or slightly up) the entire mechanism stops, and water streams back behind the boat. I can't tell if that Merc 40 has power trim or not. My guess is if you play with engine trim angle and engine height you will find a happy spot that it will neither cavitate nor dump water over the transom. It may require another prop to do it.

Alternatively maybe a piece of bent aluminum mounted below the clamp, or within the cavity of the jack plate, could block the flow of water from coming up. But it would need to clear all of the possible engine positions if it extends beyond the jack plate.

[CaptDan]

Larry, thanks again for taking the time to post pictures. When I was doing my research on building this boat I checked out several. One guide fishes his with a 50-HP Honda and it did fine with 3 people and gear.

On my Gallery I just posted pictures I took this past April of Capt Billy Henderson's Personal XF 20 transom and also one built by Joe at Storm Port. They don't seem to have their transoms any higher but they might. It may be an Optical delusion but my transom is within 1/16 of an inch of what was shown on the plans including the camber (my deck has no camber).

Ya'll are correct. "SWAPPING" motors is not an option. I want a light boat to get back in the bushes.

STUPID, STUPID ME................ I built my boat just like the cartoon. Larry do you know the transom heights of the boats you posted pictures of such a Red Alert and Aripeka's XF 20?

It looks like just for fun, I am going to have to unhang the motor and Jack Plate and build up my transom so I can figure out the prop situation. I should have a temporary tach next week for that.

[TomW1]

Dan let us talk it over among us as I am not sure you need to raise the transom. It looks pretty close to Richards. I would prefer that you get a temporary tachometer and see what your top rpm's are with the 13 pitch prop is with the engine mounted at the top of the board and the JP started just above the tunnel or where Richard might suggest it.

With the 40HP we have a difficult time propping and getting you on plane but we will do it. Hang in there. '

Tom

[cali123]

Since you already have your jackplate and motor hung , the actual measurement is not important. What is important is that no part of the motor mounting plate or jackplate is lower than the top of the tunnel. I think you should start with the motor cavitation plate about 1 inch above the top of the tunnel at its lowest position.If you think thats too high then put the motor in the middle hole (assuming that the motor has 3 adjustment holes) with the jackplate all the way down. My XF20 transom height is 26 3/4" total and 22" above the tunnel. I believe that it is a couple inches higher than Arpeka Angler's Red Alert transom.

[Aripeka Angler]

The transom on Red Alert is 20" from the top of the tunnel to the top of the transom.
I've seen bunches of Henderson skiffs. Fished on a couple as well.
Put a tape on one, it' should measure the same transom height as my boat.
Cali is right, if any part of the plate gets into the rooster of water jumping out of the tunnel it will cause your issue.
Even if the plate is slightly higher than the tunnel it can still be a problem.
Also, you really need a cupped prop. My boat will hardly plane with a un-cupped prop. A standard prop is useless on this boat...

[Cracker Larry]

Yep.