stopping a flat bottom from porpoising...
 

Have a 99' Top Gun with blower motors, 5's on boxes that run level with the bottom of the hull. Cant seem to stop it from porpoising. Once i trim up in the sweet spot and hit a wave it will start, drop the drives down and it goes away, but i can feel the boat drag and slow down, If its completely calm im fine.....What seems to be the fix for this problem? Ive tried spinning the props in and out out helps a bit...

On my 1997 Gun we lowered our X dimension a few inch's with the addition of drive spacers & we went from 87 to 94mph and also stopped running like Flipper.

Night and day difference on our hull.
Good luck!

I still have new spacers, if you can use them.

Gary

Thats why you need a constant 3' to make the hull happy... :)

X
 

Agreed, your X-Dimension is a little too high, the spacers should make a big difference. You may see an improvement with 1" spacers but 2" should be right on the mark. What length trim tabs do you have? If you don't already have them, 380's will help the combo as well.

Not mine thats for sure!
-Mike

If you are in your "sweet spot" I would use tab input rather than drive input to settle her down and then when it settles out you can ease up on the tab input. A little bit of tab goes along way and you aren't scrubbing as much speed either. I agree with everyone with respect to your X being a little high as well.

what speed is it starting at?

id call bblades and tell them what you dont like about the way the boat acts, send them your props, and try it after they do their thing. my boat chine walked and everybody told me do this and do that. i sent my props out and had them labbed, now it runs like its on rails. just a thought.....

props have helped the porpoise in my boat, more blades

i agree, if they can run the same boat with surface drives and get it dialed in, then i think playing with the props should solve your problem.......my prop shafts are 1" below the running surface and about 48" back from it.

wow, thats deep !!!!!

should be more like 1/4 inch above the runing surface,
at 48 back !

What kinda power are you running

Just curious, but did the boat come with 5's on it when it was new? 1999 is a pretty late year model to have 5's on is the only reason I ask.

If someone added the 5's afterwards, the X dimension could be off by quite a bit if they didn't adjust for the drive change & transmissions, since TRS drives were pretty much out of production by 1999 when the boat was built.

Like others have already said, I'd try either having your props redone, or buy new ones all together if it were mine. If you have a reputable prop company do the work, they should be able to eliminate the porpose for you assuming it isn't too violent. If props don't smooth it out, try spacers next.

You 99 with even a covergirl cabin is trying to carry alot of weight up front. With the "X" as high as it is your fighting a leverage problem. I agree with both opinions. Props will help but your "X" is a little too high. I would looks for a 2" spacer see how it runs, then send the props out. If you do the props first and the problem isn't fixed you are gonna have to get the props done again after the spacers. The only way to get the props right is to give the prop guys the correct information BBlades is great to work with.

i have 2" spacers that I'am going to put in this season once the weather turns around here and stops raining every day.. my props are 17.5x29 merc 4 blades, what should i try first? (more blades, different pitch, diameter?) Also my tabs are 380's i run them level with the bottom as often as i can. The boat had 3A's form the factory, and then was switched to 5's and boxes. Power is 598 tall decks, 14-71 blowers, tuned down a bit making 850hp with 3.8 psi of boost..

i would go 18 X 29P or 30P 3 blades. Bigger diameter will help you still get on plane, and 3 blades carry the bow better. find a pair and try them, what do you have to lose???? dont try going to five blades then you really wont be able to get the nose up. mess with diameter and blades, pitch is only going to get your rpm's where you want them.

I think you need more blades with 17.5 to 18 inch diameter.

more blades is going to lift the stern, but ur the guy who should know cause your running way up top. did you have the same problem??????? i love surface drives by the way...

My boat never porpoised, but it is very sensitive to props. I've never had a set of 4 blade cleavers that I was happy with (spend a fair amount of money with bblades trying to get them better). I had a set of Hoss 4 blade round ears that ran very well after bblades worked on them, but threw the blades off one of them. Now I have a set of 6 blade Herings with a high rake angle, these seem to run very well but I only have limited time on them before I tore the boat apart. Now I up-ed the power a little and lightened the boat?? We will see in the next month how it works. btw Since I switched to bblades for prop work I have been very happy with the results.

Try some different props even if the pitch isn't exactly right, you will get a feel how they carry the boat.

Kris Vogt

stick some boxes on the damn thing, it will help a lot !

i apologize for bringing this topic up again, i see that it has been dead for several years...

I have a 94 TG with 780hp blower 540's and Teague platinum drives, with labbed props, i can get 82GPS on smooth water. i still have a porpus problem though, should i look into putting extention boxes on?

this boat is new to me, and im new to the "go fast" side of boating, so i apologize if i ask a dumb question.

What props are you running? I would have bet that it would be faster than 82.

All straight bottom cigs hop until 62-64, then they lay down and run flatter, I run tab until 60, then I can raise tabs up all the way if wanted. Running 15 r, 17.75 diameter, 5 blades

Zero, how deep are your drives relative to the bottom and do you have boxes?

Yes, curious on this one too. I have porpoise problems.

17.5"dia 32P - 4 blade Merc cleaver, 5s on boxes even with bottom, 1000hp a side

Seems to run pretty good above 72-75mph, but bad porpoise where I want to cruise at 65mph without burying the tabs and using more RPM to cruise.

I want to try drive spacers, any before and after experience here? I also have a set of 32s to send to BBlades that need cupping to help planning, any experience on what was done to props to also help stop the "hop"..


<---- See, look how bad it hops in my avatar!!!

If this was true I`d put on my spacers in a second. I find it hard to believe however that putting the bullet deeper in the water would increase speed unless it really gets that hull out of the water that much. I did not notice that when I had the spacers on .. boat planed a bit better but speed was not increased. It only increased with higher X

Wild - did the handling improve at all with the spacers?

Mine loses 2-3 mph max using tab to stop the hopping.

The lower "X" gives you a little more leverage. at cruise speed the hull run a little deeper in the water. With the inherent HOP issue of all Top Guns this makes things worse. Lowering the "X" 1-2" will give you more forward push helping the HOP with a little tab. Then try prop work. I believe Gary (RPM) has a set of spacers if someone needs them.

Biggest Diameter Wheels you can find eliminated the hop on my 1993 Top Gun when I had the boat. Sky high X dimension 3A's and almost 900HP. No spacers

fill in the notched transom. that will stop the hop

It will stop hoping because you will loose 3-5 MPH...lol

I spoke with Tfarmer he said the spacers didnt make much difference. He had some kind of hook or wedge put in the bottom(wait I just spend $$ to get rid of one) but at the end of the day it seems it`s just the nature of the beast.


I`m running 17 3/4 props . That`s not exactly small.

I also remember the wedge thread - can anyone who finds it post up the link? I'll start searching......

And speaking of the wedge, does it work? Does it help the boat fly level? And who does it?

OK, found it:
http://www.offshoreonly.com/forums/c...tom-wedge.html

another:
http://www.offshoreonly.com/forums/c...2-top-gun.html

Well I had a this so called wedge believe in the form of a hook. The ride was better because the boat was plowing thru the water like a tug boat lol
I`ll stick with using tabs for transom lift.

Did you notice the flight attitude change at all?

Meaning before the bottom work "with the hook" it flew level?

and after the bottom work to make it straight or a bit of rocker it flew bow high?

I am probably most interested in this as I do not like how my boat comes out of the water and would like to correct that with the proper setup.