Annoying porpusing..........

kreed · 05-05-2009, 06:34 PM

Has anyone one experienced the bow of their boat nose diving to the left under acceleration ? Its in a Carrera ss8M with a single big block.Just started doing it after new engine. About 700 hp and 700 F/P torque. Also, the boat is porpusing after 60 MPH now. Its really annoying. I would assume the nose diving is from the torque, but how do I correct it ?

Dude! Sweet! · 05-06-2009, 05:39 PM

You may want to try PM'ing MarylandMark. I believe he knows a lot about "porpising".

onesickpantera · 05-06-2009, 06:21 PM

My 24 will "roll" to the port side under acceleration a bit. At WFO run the port tab just a touch lower and BARELY drag it to keep the boat level. 700 hp is a lot of power. More torque=more roll. If the bow is "diving" you may have the drive trimmed in too far. Try trimming it out a bit.

My boat will also porpoise if I don't use the tabs just a touch. Some props are better than others.

What prop are you running?

rchevelle71 · 05-06-2009, 09:39 PM

Also, trimming the drive up will help with the roll, not really so much with the porpoising though.

fast fun 2 · 05-07-2009, 07:19 AM

Tabs are your friend

kreed · 05-07-2009, 07:30 AM

Its a 28 bravo 1. The prop is actually alittle too big I think. But I tried a 26 bravo yesterday and the " torque roll" was worse. I think I need to try a 5 blade prop to lift the hull out of the water more. Less drag, less roll ? Maybe? Im going to talk to Hydromotive and bblabes today to see what they say. Thanks for the advice.

rchevelle71 · 05-07-2009, 08:23 AM

As far as the rolling goes, it is a light narrow beam boat, even my 24 with a 225 outboard does it under acceleration with all props except a 23 mirage, just drop the tab a bit, and trim it up. Porpoising can be helped with weight transfer, drive height, or prop selection.

kreed · 05-07-2009, 09:21 AM

Ive tried dropping the trim tab, that didnt do much at all. Driving this boat above 60 MPH can be a handful. Its not even fun. Someone needs to do some tricky prop work I think. I mean, Im not the first person to put a motor like this in this style boat. I will stay on it until I find the answer!

rchevelle71 · 05-07-2009, 09:58 AM

Quote:

Originally Posted by kreed

Ive tried dropping the trim tab, that didnt do much at all. Driving this boat above 60 MPH can be a handful. Its not even fun. Someone needs to do some tricky prop work I think. I mean, Im not the first person to put a motor like this in this style boat. I will stay on it until I find the answer!

I am not saying this is definitely going to work, but it did for me on the 24 with the 540, An old racer taught me, drop the left tab a bit, and trim up til it goes away. Of course we had big tabs on that 24, depending on what tabs your running, it may need more. Yes the prop work will help a ton if they get it right, prop work is a science, I tried all kinds of props, with no luck, then I bought a pair of old solid hub mirage 23's off Ebay, just because it was a good deal, I was going to use the righty for a spare, and even loaned the pair to Lucky Strike to try, but he didnt like the speed. One day I decided to try my spare prop, and it was the perfect prop

lukiepal · 05-07-2009, 11:33 AM

Check the hull for a hook on the bottom, I had a 33 avanti with stock 454 mags, when I put in 540s with blowers about 900hp each, the hull acted the same way as yours is, found the problem to be a hook in the hull, when fixed it rode great, the hook will act as a trim tab pulling the bow down.