OK, I'm almost there but have a few things to work out. Breif description of what I'm running 1988 32' Hydra Cat w/ T/ 700hp 540's, N/A. Imco SC's w/ -2 shorties 1.5:1 lowers. 12" Stellings boxes set at neutral/ top holes. According to my calculations that should be raised up 2 7/8" from stock however I do not know my X dim. Running B1 36P props turning out.

Boat runs great so far. No engine problems except for blowing oil out of the VC breathers which I will plumb into puke tanks over the winter. Have rev limiters set at 6K but builder says I could push to 6500. Popped a couple of uppers doing hole shots from 50mph so I have eased up on the hammer during acceleration. I know I have to re-gear the lowers to 1.34's so I can dial in the props next season but right now here's whats happening.

Smooth acceleration out of the hole, slight bit of cavitation getting up on plane then it bites and goes. At about 80mph it starts to porpose. A slow rolling porpose. Trim the nose down it gets better but run oout of trim before it goes away. Conitiues thru up to 105mph at 5K rpms where the tail starts to get loose like chine walking. Boat has more power and rpms to go.

My thoughts are the X is too high and the props are not carrying the bow. I'm thinking of starting to space down the lowers 1/2" at a time figuring that if I get more prop in the water at speed it will carry better and stabilize the rear of the boat better? Am I on the right track? Thoughts, Ideas?

I was under the impression that you can tame alot of porposing problems with prop work. If this is true, call Brett from Bblades, he can help for sure.

Try turning the props in. That could help. Cats will porpoise at some point when they transition from a boat to an air entrapment hull.
Sounds like you are running too much down trim. Try trimming it out and let it pack air. If that does not work try trimming it out even more. When you hit 90-100 mph then trim in it some. If it starts duck walking (almost like chine walking) back and forth you are trimmed in too much. Sometimes on cats I have made sweeping turns while gaining enough speed to straighten it out and let it pack air.

Props too low in the water will cause a porpoise also as the lower units cause too much drag.

I wouldn't jump to turning in, most of the guys I know picked up speed but lost handling and the boats azz is lifting out of the water turning in so its going to walk and make the nose fly high in rough water. what was the old prop shaft height how far above keel was it. did it have #4s when new and you went with b1 style drives and boxes. I could measure set back and height from the Gerrys skater this week his would be higher with 6s. theres a friend that has a motion 35 I think its b1s I could ask him if it helps. whats easier dropping a bolt slot on the box or spacer on the drive try it. it would be good to here from fountain 40 they have a motion to Dan, I'll call him.

Air time may be confusing cat and v hulls on prop rotation. Cats handle better turning in and faster turning out. Opposite of the Vhull. I have tried every combo and prop on nearly 15 cats I have owned over the years. Turning in tends to help limit some of the porpoise on some cat hulls. Every boat is different. Cats are very different to drive than a v hull. I am guessing the hull needs more trim up which tends to freak some cat owners out when the hull starts lifting up. Some guys think the up button is faster and overtrim the cats. The mention of chine walking is a symptom of not enough air under the hull. Before any major changes to drives or props try the easy stuff first.

boats azz is lifting out of the water turning in WRONG !
Artie the AIR must be thin in Easton Ma
check out his avatar he is running a Cat

faster spinning OUT as she picks up the transon ,spinning in drops the transon and carries the nose .spinning out keep an eye on water Temps raising the transon to high will short the motors on water & yes too deep will porpouise as the air being packed can't get out as the hull is stuck to the water .

Fireboat take lots of notes as things will change considerably from spacers to inboard/outboard rotation

I'll try switching the rotation first and some trim up. It did seem to get worse as I trimmed up but not having enough prop to power thru is holding me back. I have more throttle left but I know I'd be up on the limiters. Do you think I should re gear the lowers and then start over? I'm pretty confident that the boat has 115-120 in it if I can get it to settle down a bit. far as I know it was always a Bravo hull. Ran out of Kurts Marine in Brick NJ, Danny built the engines I have now and they still do the heavy work on it. Wish the season was gonna hold out a little longer so I could do more changes.

Wish the season was gonna hold out a little longer so I could do more changes DONT WE ALL !

u will be amazed at the difference when you switch the rotation and dont overtrim BIG Daddy she should power thru and run flat 4 ya

get a couple of cougars to run up front really quick...

Season isnt over tell it snows just need a bigger coat