Help with tunnel hull jet

[mckinney004]

I just got a 1648 Landau flat bottom with a jet tunnel. I mounted my Evinrude 50/35 jet on it. The mounting job seems to be good... I can run wide open and through fairly rough water without sucking air and causing cavitation or ventilation issues. I can also turn sharply with no issues. The one problem I’m having is during fast takeoff. I can ease into the throttle and take my time getting on plane, but if I punch it to jump on plane quickly, the motor spins out as if I’m having cavitation or ventilation issues. I have quite a bit of experience with jets, but none with tunnel hulls. Anyone have any thoughts? I initially thought it was a mounting height issue, but like I said everything runs great except that scenario. Thanks in advance for the input everyone.

 

[DeepCMark58A]

Pics of the set up?

 

[Sea Rider]

The motor counts with 2 lower leg horizontal plates same as traditional motors ? A pic, much better than 100 written words.

Happy Boating

 

[Bondo]

Ayuh,.... How worn is the impeller, 'n wear ring in the pump,..??

 

[mckinney004]

Sea Rider- I believe the mounting bracket is the same as a prop motor if that’s what you’re asking.

Bondo- haven’t checked them recently, but had zero problems on the previous similar boat before swapping it over. I could hammer full throttle and be on plane within a couple seconds. Makes me think it’s more of a mounting or tunnel issue. Could it just be that the intake is closer to the surface than on a standard hull? I never saw it sucking any air, but it’s not impossible.

pics coming soon.

 

[mckinney004]

 

[Grub54891]

Not an expert by any means with jets, but it looks a touch high to me. Have you tried lowering it?

 

[mckinney004]

It’s hard for me to tell for sure I the height. Normally I can use a straight edge along the bottom of the hull, but the tunnel makes that more difficult. In my experience with other jets, I mounted them as high as possible, until they cavitated when breaking onto plane or making a hard corner. That seems different here, since I have the cavitation problem almost instantly if I punch the throttle. If it only happened later as the water level dropped parallel to the bottom of the boat (tunnel), I would tend to agree. I’m hoping someone with a tunnel will see this eventually. im going to try dropping the motor 1/2” or so, but I suspect it won’t fix it since I’m able to plane out and run full throttle as long as the acceleration is somewhat slow. I’m going to experiment with height, but it might be something I just have to learn to live with. Or grow to hate.

I have two theories.

1. The motor is able to suck air from the surface as I punch the throttle since the intake is closer to the waters surface than when mounted on a standard hull. This will only get worse if I add the floatation pods on the back as I plan to do.

2. The motor being mounted higher causes the impeller to sit in a partial air pocket when floating, and it takes a slower acceleration to draw water up into the void in order to keep the impeller from spinning out.

 

[Sea Rider]

To set engine height correctly need to determine where is water flow passing by when on plane on flat calm water, with deck weight evenly distributed and engine running trimmed to 90 deg.

Ideal is for water flow at plane to skim right under small water deflector plate and bulb, if flow passes right above deflector plate water splashes upwards will be produced and slow combo down a bit.

To check engine height pull head out middle transom while on plane or have someone follow from behind to check that for you. Wild guessing raising or lowering engine is a waste of precious boating time.. Just match boat's middle water flow under splash plate.. Report your findings..

Happy Boating