baronbob

I have recently installed an M-1 procharger (5PSI) on a big-heavy cruiser powered by a 7.4 MPI. The boat comes out of the hole great with 26" cups on a bravo III with a 8" stern jack extension. The boat tries to get in the mid 40's however it porpoises eating up the speed potential. Tabs down take out the porpoise but also tax the speed down to 42MPH with the bow in the water. I straight edged the bottom near the transom and found a 1/4"-1/8" rocker. I purchased some GOOP MARINE FAST FIX which supposedly is non- sag in a bottom application. I am thinking of building a 1/4"-1/2" hook into the bottom. Any experience out there with this type of situation?

zahndok

Sounds like too much.

Panther

What kind of tabs are you running?

baronbob

Bennett tabs (not very big I would estimate 12" across and about 11" deep) and they are deflected down about 3/4" down when they stabilize the boat.

Mr Gadgets

How long of a distance for that rocker? IF you can fill in behind it a bit, take out the back side of the rocker, that would make it all hook. Does that make sense? If you measure 5' forward and the rocker is in the last foot, if you fill in behind it.. the hook would be in front of that 1' mark. You dont want too much hook or it will suck the bow down and you will go slower. Can you sand out the rocker? Make the bottom flat and see how that works.. Rocker with tabs is a negative and a positive.. Flat bottom is neutral.. IF you add anything do it in small steps.. 1/4" is a lot ..
Experiment.. experiment..

Good luck

baronbob

Thanks for all the advice. I fixed it and here is how!! The product is Goop Marine fast fix. It works great on up side down applications. No sag or tear. 5 bottles no waste on the driveway or on me. I have a 8" ride pad, dead rise and then the first lifting strake about 18" up the rise. I built a dam out of aluminum and stuck it to the transom flush with the ride pad and then tapered it to fall 1/2" below the beginning or highest point of the strake. I started out with a 1/8" rocker and if you average the new material starting out zero @ the ride pad and sloping to the maximum of 1/2" @ the strake Thats 1/4" average over 18" each side. Factor out the hook and I ended up with a 1/8" hook over 36" of a 10' wide boat. Probably only 9' wide @ the chine. Therefore 33% changed from 1/8" rocker to 1/8" hook. Bingo the Porpoising is gone.