How do I stop porpoise on 24ft cat?

[WILDMAN]

I'm setting up a 24ft Liberator, same hull as Skater, It's got 225 Johnson HO's and runs 86-90. I've tried different props, setbacks, engine hieghts, and weight distribution, and still have a porpoise problem. I've only tested it on a small lake that's dead calm, so I'm sure that may be part of it. Other that that, is this always a problem? It hops at 60 and above! Any suggestions are welcome. We're setting up 2 more with merc 2.5's and one with 300x's.

[24RODjr]

MORE POWER!!!
Got me man. I have a 24ft tunnel that is prone to porpoise a bit, but I found that with more pitch, it did it less...

[jm2drvr]

I've never driven an outboard before, but on my io cat when it is dead flat calm, I hold the boat on a slight (very slight) turn. This will imidiately stop the porpoise, I'm sure this will work for your outboard version also. I eventualy added hydraulic trim tabs which took care of the problem in flat water altogether. Good luck and hope this helps!

[stanpace]

WILDMAN CHECK TO SEE IF THE HULL HAS A HOOK IN THE BOTTOM. TRY ANOTHER INCH OF PITCH ON THE PROP OR ADD MORE CUP TO THE PROP, THIS WILL GIVE MORE BITE TO THE WATER AND THEREFORE LESS PORPOISE. THIS IS A STUPID QUESTION, BUT ARE TRIMMING DOWN BEFORE YOU PULL BACK ON THE THROTTLE? IF YOU PORPOISE AT 60+, LOOK FOR MORE BITE.

[Whatboat]

Solid motor mounts help, Have you tried a four blade? A Friend has the same problem, been working on it all summer. Let us know what helps.

[WILDMAN]

I've tried 30 cleavers, 34 cleavers, and 30 roundears. They all do it. I've run it WOT and played with the trim. Does'nt help! I talked to Skatermike today, and he said, " If it's calm, It's gonna porpoise" His 24 Skater does it 45-70 mph. Mine does it 60-85! I know more power will help, but this boat's already rigged. I'm going to run it on a big lake this weekend and see if a chop helps. Wish me luck http://

[flyinbrian]

My Skater porpoises like mad on flat water. Find a light head wind and some good 1'-2' chop, keep the trim neutral to negative and run the cleavers.

[Skaterfast]

I'm pretty sure what is happening is the tunnel is finaly passing air at 60.This is what is making it porpoise.Because the boat is not going fast enough to cary the bow it lifts then drops in a never ending cycle.In theory what one might do is put round ear bow lifting props on the boat.Beleive it or not this is the exact oposite of what you should do,because you already have more than enough bow lift with this bottom design.Any way there are 2 solutions.First solution is to put on some trim tabs.I'm in favor of solution #2 because it costs you nothing.And that solution is,not drive it at 60mph.

[steve@kps]

NOT trying to get prop business, but...i've worked w/ some boats w/ that problem.
see your local prop guy and talk to him
add 2 deg. more pitch, and reduce the rake angle by 2 deg. and take out some cup.
Just like skaterfast, it's the opposite of what your thinking.
Fast hulls don't need help lifting from the prop and that's what rake does. Similar to drag boats, etc.
Hope this helps.
steve g.

[Brad Zastrow]

Save your money on the props, light cats are going to porpoise. Flat water is only going to make it worse. The boat is making the transition from a boat to a airplane. It is getting lift and then spilling the air at that speed. Here is what you can do: As silly as this sounds do not cruise at that speed, either speed up or slow down. Also you can turn slightly to spill off the air until you get to the speed that will hold the hull up. After about 75mph your boat should level off. I have owned 6 high performance, light weight cats from 20' to 35', inboard, outboard and all have porpoised at a certain speed. Cleavers tend to run the best on light cats.

[bulldogdad]

wildman you still having problems with that rig?don't know much about them but i have seen a center trim tab for tunnels,anyone here heard of them,help wildman out please :D

[dorC]

Hey Brad, hows that coverted 35 working for you?

[Brad Zastrow]

The 35 Motion Baker Marine converted from a two seat to a four seater is "scaryfast". 100 mph and it will just cruise at 2/3 throttle (2,000 hp and #6's). Interior turned out really nice. 4 bucket seats, five point harness belts for everyone, intercom system, oxygen tank (just in case), GPS speedos front and rear console. A lot of fun. :D

[WILDMAN]

The 24 still hops on calm water. I had it out in 1-2ft chop, and it goes away. I just setup another 24 last week with Merc 260's. Awesome acceleration! On flat water it hops until 80 mph or so then flattens out. The slight turn thing works well if you don't need to go straight. I took the Merc powered cat out in 3ft crap Sat, and it flys at 90 plus over that stuff! Totally awesome feeling! I raised the motors yesterday and picked up 6 more mph. It was on flat water at 98 mph. Will choppy water add more speed? It's a new 2003 24 LIberator. I had it sold for $68,000, with the refusal option if it did'nt do 100 mph. Well, he took his deposit back. Anyone interested? The OMC powered one is a 2002 and is $52,000. Email at liberatorboats@yahoo.com for pics. See-ya WILDMAN

[dorC]

So, does that mean that you're now a convert? :D

[Skaterfast]

On a good day my 24 Skater with 225 Promaxs will do just over 100mph.I'm setting the motors back 6" to maybe get 105mph.Keep playing with the set up.A 24 Skater with twin 260's should go over 110mph.Does the boat weigh less than 3400lbs?It should.

[Brad Zastrow]

Tht boat should run 100+ with 260's. Yuo say it is a Skater splash? A true Skater would run that fast, a variable could be the weight of the boat. Setup will get your there if it is not a heavy boat. Engine height is important!!!!! Test, test, test. 1/4 inch at time will suprise you. Too high is when the boat wants to wander side to side (prop walk) or water pressure starts to go away. Probably worry about water pressure before you get so high it walks around. Neutral trim should be the fastest angle of attack. Make sure to have a dual trim gauge to keep the motors even with each other. It really hard to tell just looking back. Cleavers props will get you more speed and all around performance will be the best by far. I will guess Merc 15" x 32" three blade labs will be faster. Are you turning the props in or out? Turning in will be faster in most cases and may help the porpoise issue. Turning props in will give a slightly loser feel to the boat when turning the boat. I run mine that way. Also check to make sure the motors are aligned. Propshafts and nose cones same distance apart. Sometimes a slight toe-in or toe-out of 1/8" to counteract the prop rotation and the slop in the steering, depending on props in or out. Boat should run 105-110 with 260's or 280's Mercs.

[Charley]

Brad Zastrow:
Tht boat should run 100+ with 260's. Yuo say it is a Skater splash? A true Skater would run that fast, a variable could be the weight of the boat. Setup will get your there if it is not a heavy boat. Engine height is important!!!!! Test, test, test. 1/4 inch at time will suprise you. Too high is when the boat wants to wander side to side (prop walk) or water pressure starts to go away. Probably worry about water pressure before you get so high it walks around. Neutral trim should be the fastest angle of attack. Make sure to have a dual trim gauge to keep the motors even with each other. It really hard to tell just looking back. Cleavers props will get you more speed and all around performance will be the best by far. I will guess Merc 15" x 32" three blade labs will be faster. Are you turning the props in or out? Turning in will be faster in most cases and may help the porpoise issue. Turning props in will give a slightly loser feel to the boat when turning the boat. I run mine that way. Also check to make sure the motors are aligned. Propshafts and nose cones same distance apart. Sometimes a slight toe-in or toe-out of 1/8" to counteract the prop rotation and the slop in the steering, depending on props in or out. Boat should run 105-110 with 260's or 280's Mercs.Brad really knows his stuff! but...he does have 3 boats :D hahahaha..... my thoughts to add were gas tank placement and if the "Splash" was vaccume bagged on the layup.... those 2 things, I would think... could easily cost you 10mph or more in that small of a boat...

[WILDMAN]

Brad, will running in a 1-2ft chop be faster than calm water? How much faster? I'm turning the 30 cleavers out.

[Brad Zastrow]

In most cases a little chop will be faster.

[jolley]

O.K. I have a 26foot Ocean Express it hops on flat at full bore, but I can't drive through it! I'd like to find out where I can buy a ballast tank preferably a collapsing one instead of a small fuel tank. So I can pump in weight on flat water dump it in the rough.Anybody know who has 'em? thx. Bill :p