drive height
 

Ok, I got the drive hung today. It looks like the prop shaft is centered on the bottom of the hull. I have an adjustable extension box, but due to the step and rub rail I can only move it 1/2" each way. What are people's opinons as to how well the boat will plane vs. how it will run with this drive height? The application is on a tri hull single step cat. The center sponson is about 1/2" lower than the outer ones.

Cord that sounds pretty high. If I understand correctly that the propshaft is in line with the hull bottom. I would think it would be hard to plane. A 5 blade prop might be worth a try.

Eric

Yea, that's what I'm fearing...

Most cats run with the X up higher then the bottom that is why they suck to get on plane some times. I would just give it a try and see what happens. If you need to you can get one of those spacers.

Jon

My experience is with 21 Eliminator O/B and a couple twin engine Chris Cats. Depending on setback and weight distribution, it sounds like you're pretty close. The cris cats ran well even 1"up from the bottom (4 blade cleavers on speedmasters). The eliminator was even higher.
How long is the extension box, what kind of drive? I wouldn't doubt that you could easily run 1-2" up from the bottom with 10" setback, especially with a 4 blade.
Gary

I have a 12" box on. The drive is a bravo with a 2" imco lower.

I would start with it all the way up and bring a saw to cut your rub rail. Depending on what kind of cat, most of the boats bow lift is going to be genetated by air at high speed, so a lot of trim control is not necessary. Keep raising it until it has problems getting on plane or blows out easily. With that much setback and a notched transom (step?), I think you'll want to start at about 1" above the bottom.
Gary

Is there a step on the center pod? I agree with Gary with 12" of setback I think you are going to be way low.
I know on the Chris Cat 2" above the bottom is to low without boxes and 4"-6" with 10"-12" set back.

mike

Cord,
Did you get FireHawks recommendation on the drive height? I would think they could give you some sound advice.

Paul

Really! The prop shaft can be above the bottom? I'm just trying to picture how the water is flowing off the bottom in order for the prop to bite. Here I was fearing that I'd have to go down an inch!

Katdrvr-yes, the center pod is stepped and notched.

PB-Firehawk said that the gimble was cut for 19.5" x-dim. The boat was originally set up to run a blackhawk and no box. With me using the 2" shortie drive and a box, I have absolutly no idea where that puts me for a x-dim. But I believe that the blackhawk would have been another 5" above my current height.

AHHHHH. I forgot it was originaly set up for the blackhawk. Sounds like it will be trial and error
to get it dialed in. Then again what isn't. Hopefully with no error. Good luck.

BTW, that Interthane Plus looks AWESOME. Like a black mirror!! Time to start rigging!! Oh, and the respirator was a MUST!!!! Thanks for your help.

Paul

As the hull moves through the water as the water passes the transom the water rises.

On my Chris Cat I was told to take a straight edge and lay it along the bottom so it rests on the step and run it back passed the transom, this will establish the true line of the hull. Take your measurements from the straight edge. I don't know if that will work on you boat or not.

I know on my Chris Cat if I measure the drive height with the straight edge method the drive is about 1 inch lower than just lining it up with the bottom edge of the transom.

Can you put spacers in your drive to make it longer? If you can I would mount the drive as high as you can and just add spacers if you need to lower the drive. Also your prop choice can make a big difference in how the boat with plane.

mike