Jackplate causing boat to porpoise ???

[tvpear12]

ok, I installed a right hite jack plate to the back of my 1989 tracker Tournament 1600 TF 16 foot fiberglass hull with my 1992 90 horse v-4 cross flow to lower the cavatation plate to about 1" above the bottom of the boat. Now my hole shot is great with my 13x19 prop, but when i am trimmed out and pull throttle back about half way the bow starts to bounce and makes it hard to controll when going into a turn, not to mention how goofy it must look to other people as this thing is probably looking like a low rider with hydrolics. any one know how to stop this other than trimming down, tell me. sometimes i will need to turn before i can get it trimmed down but dont want to take some of these turns a wot. thanks for any help. P.S. The jack plate is a 5" set back if this makes a diff. Speed is 48 mph at wot.

 

[LubeDude]

Re: Jackplate causing boat to porpoise ???

There is nothing wrong. You cannot have the engine trimmed full up at much of anything under WOT or most any boat will porpose. As safe practice, allways trim down when negotiating a turn, We all do, Mostly because we have to.<br /><br />With the jack plate, you could probably raise the engine another inch or maybe two.

 

[tvpear12]

Re: Jackplate causing boat to porpoise ???

Thank you comander. before i installed the jack plate the cavitation plate was about 3" above the bottom of the hull and it seemed to vetilate at full trim and wot. do you think i can put it back at the same height is was and not ventilate? does the jack plate play that much of a roll in this? P.S. my hull is a stepped hull so do i measure from the bottom of the hull or the transom?

 

[WillyBWright]

Re: Jackplate causing boat to porpoise ???

Play with the height until you get a good compromise between speed and control. With a stepped hull and a jackplate, it's difficult to determine where the surface of the water will be when the boat is on plane. With a transom that goes all the way to the waterline and no jackplate, the surface is easily predictable. That's really the determining factor, not the bottom of the hull so much as the surface of the water. You might want to consider trim tabs to control the porpoising.

 

[MarkHPCA]

Re: Jackplate causing boat to porpoise ???

If you are going to play with the height be carefull of your water pressure. If you don't have a pressure gauge GET ONE. They are a LOT cheaper than an engine re-build at about $30 for a complete kit.<br /><br />I agree with Lube, when I added a 5" setback palte to my 'Stream it would bounce all over if trimmed out at anythng less than 50MPH. Raising the motor helped a lot. As stated before trim in before turns or slowing down and you should be fine.