#6 Top Gun straight bottom drive height
 

I have a factory #6 95 Top Gun, appropriately named the Kangaroo Rat because it hops like a Kangaroo. This is more than the standard Top Gun porpoise, this gets violent at high speeds unless the boat is run extremely wet. Talking to people familiar with the boat from way back when, I have gotten conflicting reports on whether the boat came factory with boxes or not. Everybody did say though that back when this boat was new, it handled like it was on rails and it was very fast. It is neither of those things for me. Right now it does not have boxes and has wet sump 6's. I think the drive height may just be too high and this could be a significant part of the problem. When trimming up, when the porpoise starts it feels like the props are losing bite and the bow comes down, then they regain bite and the process starts all over. I would like to know where these drives should be height wise for the best performance. I have tried various diameter 4 blade and 5 blade props, spinning in or spinning out, and nothing simple like that is helping the issue. If anybody familiar with these boats and this setup could shed some light on what drive height works best I would greatly appreciate it.

wheres the prop shaft sitting now

Old school II prop shafts are 1” below the running surface, when I ran that boat a few years ago it had a slight porpoise with one set of props, bad porpoise with the others. I know they were both 4 blades but don’t remember any other specs.

1" below the notch.

Does it still have ten tons of stereo equipment in it? I'm guessing that doesn't help the CG

how about in relation to the bottom of the boat?

top of the notch ?

It doesn't have all the equipment, but it still has a fair bit of it, yes. She's a girthy girl.

The drives are 1" below the top of the notch or 2&1/4" above the bottom of the boat inline with the propshafts.

being that high, I’m sure that boat had boxes on it before. Put a 1.5” spacer in and it should help a ton

It took a while to get used to running that boat. It was also set up to run over 100 with big power, so it took some time to figure it out after going with the NA motors. After figuring that out, I never had "porpoise" problems. It didn't like trim under 60 or so, but when you started trimming it, you had to do it a little bit at a time and let it settle. It was quite a change from a Bravo Bullet, which you could let an 8 year old drive it and not worry!!! ;) :D LOL

I think you'll find Old School's advise spot on. I have to run negative drive trim and drag some tab in any configuration other than 3/4 power and above. Even at WOT I lose speed at any drive trim setting above +3. I have a Tiger btw.........

Good to hear from you Matt. It's been a while brother.

When that boat was here on the west coast in the 90s it had standoff boxes on it and it ran through anything. I don't remember any porpoise but it was a heavy *****.

I found my boat improved significantly in that department when I lowered the boxes 1" down .(more so then a 2" spacers)
maybe something to do with the 'point on impact' on the hull.

Thanks, I had to put the boat in a time out for a while. Dropping a valve after 60 hours was just a kick in the balls. It's been 2 years and I have been running around on my 29 Fountain with a Whipple, but it's no Cigarette. I'm finally ready to make the Rat great again. I really love the big ugly turd, and most importantly so does my family so she's getting rebuilt again and will hopefully be better than ever.

I'm ok with heavy, I'm ok with not being super fast, but I am not ok with it bouncing around like a Jack Russel Terrier all the time, which is how it is now. It must have had boxes on it, that's the only thing that explains why they would be mounted so high in the first place. I'm going to try 2" spacers which should get me about inline with the bottom of the boat and see how it runs, if it's a significant improvement I will be thrilled.

Just out of curiosity Matt did the boat sit on the trailer for any length of time? Maybe its starting more and more to fight a little hook?

Yes, it did sit on a trailer that was too short for the boat for quite some time, but it does not have a hook in it that I can find. I talked to Tres Martin about it at one point and when I brought that up he actually laughed and said yeah, there won't be a hook. The way Cigarette laid up those Top Guns you could put that boat on a trailer 5 feet to short and it isn't going to hook the hull.

Man! I blew my .02 cents worth in one post! haha
Seriously though, If anyone would know I’d trust Tres for sure. At least thats something you’ve already ruled out. So, is really the only variable the fact that the boat doesnt currently have boxes on it?

The only boats that are getting a hook from that are cheap production boats with gaps all around the stringer core material.

To the best of my knowledge. Going to install some 2" spacers and see how it does. Unfortunately it will be next season before I have results.

Sheesh! Cliff hanger! This feels like the season finale of the tiger king!