Annoying porpusing..........
 

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 ?

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

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?

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

Tabs are your friend :drink:

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.

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.

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! :angry-smiley-038:

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:eek::drink:

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.

Ironman had big power in his 24. I had the boat with a 330 and didn't notice any issues. Mirage 23 prop.

HMMMM,

did you say Mirage 23??? Thats the same Best prop I am using, and what we used on Scotts 24(although his may have been a 25):eek: Unfortunately, I think he has too much power for that:drink:

That's what I think I had on there. I'm going to see the boat tomorrow so I'll check. Don't remember what Chris had on it, but I'm sure it was a bigger wheel.

I can tell you my boat HATED a stock Bravo prop. Rolled the boat to port and didn't have enough bow lift. Threw the boat all over the place, especially in choppy water.

My boat seems to like 3 blade props better. For all out speed I still haven't beat the standard Mirage(non-plus) and I have tried a lot of props. Last year I tried a Turbo 27 and it was close but then I blew out the rubber hub. I plan on testing it more this year.

The Rev4 was by far the best 4-blade prop I tried out of the box.

Try a Mirage or Mirage Plus 27 and see how it handles.

The 24 with 600+ HP ran the fastest with a 29P regular Mirage, not the plus.

I have it still for sale if anyone is interested.

Kirk

Hi guys-
Talked to BBlades today. Very nice guy Brett. He recommended something that no one had said yet......put a left hand rotation prop on the boat. With the 700 f/p torque driving the bow to the Left, the LH rotation prop should counteract that. He said that its pretty common in 27 to 29 ft fountains to have this problem when they put big power in them. Sounds reasonable. He also mentioned the hook in the hull, if I cant fix the problem with proping. That will be alittle down the road. So Ive borrowed a 26 LH bravo 1 to try tomorrow afternoon. Just to see if the boat rides straight at high speeds, then Ill find the right size prop. I just need to remember that when I shift in reverse, the boat will go forward!!!!!!!!!!!!!!!!! :eek::eek::eek:

We have already tried that, it helps, but doesnt cure it, between that and prop work though you might get rid of it.

your sprinkling on my parade. I really need to sleep tonight!! Im growing tired of thinking about this 24 HRS a day. Looking forward to trying this prop switch tomorrow so HOPEFULLY I can move on. Ill be happy if it goes 70 without leaning, at this point.Had NO problems with 450 HP and a 23p 3 blade prop lat year. I definatly will consider trying a 3 blade if you guys think it will help.....................

IMO...definitely try a 3 blade.

550hp in my 24, liked the Mir+ best.
never tried a Mir thou.
Wasn't too fond of the B1.

Sorry,

If you have access to a lefty, try it, I hope it works for you.But here we go back to the 23 3 blade again ("NO problems with 450 HP and a 23p 3 blade prop lat year"), I know you need more than 23, but I think 3 blade is going to be the ticket.

tried a 26 P LH 4 blade yesterday...........worked great!!! :evilb: BUT, I am going to try a 27 3 blade also. LH and RH to see which one works better. Cant get my paws on the 3 blades till Monday. For now I can play w/ the 26LH.

Glad things are moving in the right direction.