Jo
My drive is 4" below on my 28 with a Troy Dennis 731hp dynoed engine.You told me to try going down 1".What is the height of the 95 28 with 647hp that runs 86mph? Anyone's response would be greatly appreciated before I purchase a new drive.This boat is Too Old's old boat.
Steve

First, what are you trying to accomplish and what is the boat doing now???? Bow lift??? Reduce slip %????

I have a '96 with a notched transom and my propshaft is about 3.5" below the bottom. It is higher than I want it and I may be lowering it an inch this summer. I just can't get enough leverage to lift the bow. Imco just started making a 2.5 and 3 inch spacers and I already have a 2" on it.
I'm looking for both bow lift and slip reduction. I'm getting the prop reworked for more bow lift/less stern lift and should be testing it SOON. I hope it helps.
If you search through all the old threads in the Pantera section, there are a few more about X dimension.

Hi Guys,

Question: does x-dimension really affect slip tha tmuch? I guessas I am asking I can see that it might. Any thoughts?

Here my simple mans analogy.

Stand in a pool with your arm about a foot under the water. Push your arn through the water. Then repeat about 6 inches, then right under the surface then breaking the surface. You'll find it gets easier to push your arm the closer to the surface you get.

The more water around the prop the more it will bite (for lack of a technical term).

Is my anoalogy correct?

The deeper the water, the denser.
But getting the prop higher should increase RPM.
There should be a happy medium.

i think i need to get into this thread...

im only 2 3/4" below the bottom (prop shaft) and i still need to come down. way too much slip from what im seeing with your boats. i dont think the X is as important as how deep the prop is in the water. With shorter lowers and spacers, we could be all over the place. Where is the best succesful setup. anyone that feels that they are as efficient as can be should post their drive height.

I like the picture Bruce. As far as drive height goes I heard an old rule of thumb that you can gain about 1 mph for every 1" of height increase at about 60mph. Problem with this is that once you go too high you loose more than 2mph for every inch too high due to the leverage loss. The only non cat hulls that I have seen that can run the propshaft within 2" of the bottom successfully are the superlight hulls like a hydrostream or allison, shallow V with outboards. So with a Bravo drive on a deep V let's say that the deepest the drive can run is 8" below the bottom (16" max prop diameter) and the highest it can go to still get some leverage is 3" below the bottom. Now to narrow it down some more 8" below is way too conservative for a 70-90mph boat, on most hulls 6" below the bottom is good for any stainless prop as the deepest you would want the shaft. Ok now we have basically a 3" window to find the optimum drive height. Personally I think that 5" below the bottom is a safe bet for todays props like the B1 as a deepest limit. So If I had a Bravo drive on my boat I would install it at a point that puts the shaft 3" below the bottom and then space it down 1" and retest, Then down another 1" and test and then by 1/2" increments if you really have the time and motivation. The shaft on my 24 is about 5" below the bottom, I have tons of leverage to lift the bow with any prop I use. It is cheaper and easier to lower the drive than raise it so I wish mine was much higher than it is. Every boat is different and will require a slightly different height to maximize its potential. I would predict that the shaft should be about 4 1/2" below the bottom on theese boats.
I am sure that Jo will chime in with the real correct figures.

If you are wondering if I think about drive heights and props every day You are right!!! The Ironman.

thanks..very informative

Bruce, It looks to me that your problem is solved. Its just a matter of doin it

as soon as week get the motor back in, we will put a standard length lower on adding 2". We will then be 4 3/4" below. and see what happens. P-2 here we come