Outboard jet problem

[Cfriday12]

This past week I just purchased a used 2010 Lowe R1860CJ with a tunnel hull. Powering it I have a 2010 Mercury Optimax 115/80 Jet. It is mounted with a manual jack plate. The boats tunnel hull is 14 inches wide at the top of the tunnel. When I plane the boat out it feels and looks like it is squatting a little in the rear end, and if its squatting I know I am not going to be able to run real shallow. Typically when you get on plane you can bump the trim on the motor up a little and really sit the nose down, but when I bump my trim up it starts splashing water into the back of the boat and does not bring the nose down. I have a splash guard on it. My question is exactly what height should I mount my motor to the tunnel. Should it be flush with the top of the tunnel? Currently it looks to be about 1" to 1/2" to low from being flush. Everything i have read says to mount it flush, but where it is out now the jet outtake is already about halfway out of the water, so if I move it up flush it will barely be in the water. Also, the boat is only running about 28 MPH and I believe it should run faster than that. I think I need to move it down just from driving it, but everything I read says mount it flush with the tunnel. Has anyone else experienced any problems similar. Any tips would be greatly appreciated.

 

[wired247]

Re: Outboard jet problem

I ran a 150/105 on mine for a little while until I pulled that stupid jet off and put a prop lower on it.

Had the best results drawing a line directly from the bottom of the pad to the front edge of the jet intake . Any higher it suck air on turns. Any lower and it would drag through the water and drop the stern. Forget you have a trim with a jet. Set it and forget it. Its the intake you need to worry about. Not the jet nozzle.

FWIW I was hitting 50 MPH with the jet with the timing control and rev limiter disconnected.

 

[Cfriday12]

Re: Outboard jet problem

When you say drawing a line from the bottom of the pad, are you referring to the bottom of the hull or the top of the tunnel? I guess my real question is. What is a pad? When you had yours were you able to run shallow water? If so how shallow could you run it.

 

[Cfriday12]

Re: Outboard jet problem

Also, did you have a tunnel hull on your boat?

 

[wired247]

Re: Outboard jet problem

Mine was not a tunnel . Shallow V with a pad ( foot wide flat in the center ) In your case you'd be going from the top of the tunnel as a reference. Otherwise that jet foot is going to be a plow. I could run in 3-5 inches of water as long as I didnt stop but in your case with a Lowe tunnel its not going to be that simple. Low jet boats arent true tunnels though.

 

[Cfriday12]

Re: Outboard jet problem

I just spoke with a guy at Lowe boats. He said I should mount my motor so that the foot is 3/4" to an inch lower than the top of the tunnel. Which is currently where it is mounted. Also, he said to bend the thin strips of aluminum that are at the bottom of the hull down to act as trim tabs. He said this should pick my stern up and lower my bow so I can run shallower. You can see the strips in this picture right at the bottom of the hull. Has anyone tried this? Does anyone think that will make a difference.

 

[wired247]

Re: Outboard jet problem

Personally I'd try it a bit higher than that. 1/4's of inches make a lot of difference with outboard jets. Have someone watch your jet foot while its running and see if the the leading edge is plowing through the water. If you have water spraying back off the jet while at speed thats a sure sign its too low.

 

[Cfriday12]

Re: Outboard jet problem

Ok. I'm going to toy with it, and I'll post an outcome later thanks.

 

[Mi duckdown]

Re: Outboard jet problem

Cfriday12 The Pic you posted did not show motor to transom height, At least not on my computer.
Jets on boats are a manner of 1/4" adjustments up and down. Once set properly, trim most times not needed.

 

[Cfriday12]

Re: Outboard jet problem

In the previous picture, I was showing the aluminum tabs at the bottom of my hull asking if anyone had ever tried to bend them down and use them as trim tabs. Here is a picture of my foot . Does anyone know the ideal degree angle of your intake?

 

[Cfriday12]

Re: Outboard jet problem

 

[Mi duckdown]

Re: Outboard jet problem

Motor too low. needs to be raised aboat 2"s at least, maybe more since it is a tunnel.

 

[Outsider]

Re: Outboard jet problem

Your concern should be with how the jet intersects the water, relationship to the tunnel is irrelevant. Try trimming you motor out some to a position with only a slight angle (relative to the water surface when planed out), the lower the plate until the jet leading edge is an RCH above the water surface when planed. Whatever those strips are, they likely won't make decent trim tabs. As mentioned, jets do not respond well to conventional 'trimming', and they require an undisturbed water intake or the impeller ventilates. Good luck with it, they are fun ... :joyous:

 

[Cfriday12]

Re: Outboard jet problem

This morning I raised my motor up a 1/2 inch. I have now gained 4 MPH and the boat planes out really well. The back no longer squats and I ran it in about 6 inches of water. It will run shallower but this is my 1st jet, so I'm going to get the feel of it before I start trying to run it really shallow. Thanks for y'all's feedback and help.