Jet foot height

Just got this boat had it out a few times at first the foot was about an inch below the tunnel extension and got a lot of spray and drag so I raised it up even with extension and got some heavy cavitation and still spray up into the boat so now I moved down just below the extension and tucked it in a hole to get it directly under the extension any other suggestions to help not gonna get back out til this weekend or next week so got some time to do some adjustments if need be thanks

By looking at the first pic, I would guess that the steps are causing your cavitation. By lowering like it was, it would cause drag but you were getting clean water. I would smooth out the steps with some tiger hair.

I though about that after looking at other designs. Get rid of the piece in the middle and just attach the top piece of aluminum directly to the bottom idk why that plastic is in there but I'll give that a go

The jackplate pushes the motor back farther which might be causing more spray. That step can't be helping though so try it without that first.

Something I've learned and you may already know is that spray and cavitation are two separate issues, which are both usually handled with those plates. I'd get the cavitation worked out first then build a plate to deal with the spray.

Moving the engine back away from the boat with a jack plate adds to the spray problem but I've seen some people take care of it with a spray plate attached to the bottom of the jack plate.

Jd,

I just went through this on my 3rd jet boat. From what I can tell your to high now, here are pics of mine based directly on Dick Stallman's drawings. The intake fins help tremendously! My boat handles like a Porsche now, I slide over a gravel bar and the foot never touched so it's in the tunnel as it should be. Hope this helps, be safe!

Steve

Did you make those fins or did you buy them I already took out the step and made it more smooth of a transition from boat to the extension gonna try it like this if that doesn't work gonna have the sides of tunnel extended out also I'm more worried about the cavitation then the spray but I would like to get both fixed eventually thanks for the replies

Did some measuring and don't even need the jack plate so I took that off now the foot sits a lot closer to the tunnel and is tucked under extension

You might not need the extension with it tucked in but it's definitely worth trying it with and without it to see what the difference is.

jd4x426 said:

Did you make those fins or did you buy them I already took out the step and made it more smooth of a transition from boat to the extension gonna try it like this if that doesn't work gonna have the sides of tunnel extended out also I'm more worried about the cavitation then the spray but I would like to get both fixed eventually thanks for the replies

Click to expand...

You can purchase the intake fins directly from Outboard Jets, a set runs around $50.00 but work great if your having any cavitation issues.

Good luck with it!

Steve

You can now raise the motor about an additional inch until it touches the extension. I would also suggest that you extend the sides of the extension as well. I sell jet boats that are built for me by a prominent manufacturer. I specify a stahlman tunnel, but it is made of one piece 3/16 plate, and the tunnel top and sides extend 6 inches past the transom. I typically mount the motor high so that it touches the underside of the extension when tucked in. I have never had a boat cavitate and spray is minimal. I have mounted 60 to 125 HP jets on the 1756s with no problems. The boats are rated to 90 HP at the pump, but customers have mounted as high as 150s (100HP at the pump) successfully.The intake scoops do work if you have a questionable setup, but I have never needed one on one of my boats. If you have low speed steering issues jet wings help, as does trimming the motor up during low speed maneuvers.