24 Active Thunder Cat hull set up questions

**2017 Liberator Stealth** · 07-02-2021, 05:58 AM

New to twin cat hull set up so I have some start from scratch set up questions. First. some boat history and info. Boat is 24 feet, light race lay up, hull 1700 pounds 1990 Active thunder built cat hull. From what I have learned about the boat so far is that not too many of these hulls were built for outboards. Boat came new with 2.4 245 EFI motors. When buddy got it it had twin 245 2.5 carb motors. Boat would run high 80s. Well not fast enough! But boat did not chine walk or porpoise and we ran 28 cleavers. Boat came right out of the hole no slip and take off good, ran smooth all the way to 86 mph. So we sold the 2.5s and put on a set of 300x motors. When we mounted the motors we decided to try them an inch higher than the 2.5s to start with. Well needless to say we have a totally different boat. The 300s came with 3 sets of props, all cleavers, all 34p but 141/4, 14.5 and 15 x34. So with the more low end and less RPMs the 300s provide, we started with the 15 x 34 and an inch higher than the 2.5s were. This boat has 12 inch set backs. So like I said a totally different boat, it chine walks valiantly at 85 plus and porpoises all the way to 85 and because of the chine walk the most we could get was 93 mph and that's about it. So we lowered the motors and the boat settled down, a little easier to handle and didnt loose any speed. 93 mph at 5500 rpm. I am a STV, Stealth, single engine 1 3/4 above the pad kinda guy so this no pad twin engine low rpm chine walking porpoising stepped hull thing has got me scratching my head.

First question: how do you come up with the correct prop shaft Hight on a cat? Up till you loose water pressure like any other or what?
#2. Can these motors really turn 6800 safely? That is what the sticker on the mid says max RPM is.
#3. Does a 15 x 30 4 blade cleaver sound like a possibility? Or more like a set of 30 or 32p 3 blade?
#4 I hope we have not put to much weight on the back of this boat and have thrown off our yeng and yang so to speak.
#5 Help, Help Cat people!

Thanks, Liberator Stealth.

**mistah_max** · 07-02-2021, 07:13 AM

imo your'e over propped. i have a single 300x on a 22 talon that weighs around 2300lbs fueld up and ready to go, and i can turn it mid 6's with a 30 bravo 1 no problem. 62-6300 with a 32 bravo. 15in diameter runs good with those big cases but you need to come up rpm wise.

what gears do you have?

**2017 Liberator Stealth** · 07-02-2021, 12:35 PM

Yes, I am sure of the over prop situation, but I need to get motor height worked out before I can settle on a pitch to start dialing in the boat. I would think it would be the same as finding the prop shaft sweet spot like any other boat but not sure about the twin cat hull. I need to get my RPMs up for sure.