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Running a Cat

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Old 08-07-2002, 11:28 AM
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Default Running a Cat

Okay all you cat guys,I have finally finished the restoration of my 1987 Maelstrom cat.It is powered by twin small block 425hp with all the goodies,(forged everything aluminum heads,etc)I have Kaama drives turning 15.75x26 three blade props.This is my first cat and I am taking it slow.They are totally different from a v hull.The boat is beautiful and I love it and it turns heads.
I have had it up to only 4000rpm and the gps only reads 45mph.This equalls out to 45%slip factor.I talked to Marc at Bam and he says that the hull is not over the hump yet and will see better speeds at a lower RPM once it is there.I would love to recieve all inputs from anybody with experince or Knowledge on cats,and how to drive them and trim them(with the surface drives)I will post pictures as soon as I can figure out how to do it.(I can fix and rebuild boats but barely know how to turn on a computer)You can either post here or email me at [email protected] or feel free to call at 770-920-1444 or cell 678-522-4873.I look forward to everybody's input.Thanks Mark
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Old 08-07-2002, 12:07 PM
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How to drive a cat ?
3 hail Marry's and throttle forward !!!
I'm no expert but all cats are a bit different . Your's has a center pod right ? With that power ,it sounds like you don't have enough prop unless you have a higher ratio in the drive . Your twin disc model 502 trans are a 1.5 to 1 ratio and you drives have a ratio also . You should use long hub props not short ones .(more bite) . You may benefit from 4 blades too . surface drives on cats don't need much trim if any . My arnesons are fixed mounted and work fine . ON my old 40' formula ,the Kaamas only needed a tiny adjustment to get that big battle wagon on plane . I had 17 1/2x 24 3 blades short hubs . needed bigger props . Surface drives run their fastest when they are perfectly level with the bottom (unless the boat has a problem ) . I'm sure you will get much more input from the board . This is just a little taste ! Good luck with it . And WELCOME TO THE CAT HOUSE !
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Old 08-07-2002, 12:10 PM
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I just noticed your prop diameter . You may be better with a larger diameter too . 17 1/2 is the norm . some 18's around once in a while . Remeber ,you have little, to no blade in the water at speed with surface drives You need all the bite you can get . such as big diameter , long hub , and /or 4 blades .
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Old 08-07-2002, 12:10 PM
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I do not think you will find to many boaters familar with the hull or the drives. 45% slip is really high. Over the hump? The boat is going to run out of rpm before it starts packing air. Most cats pack air at speeds of 60-80mph. Some bigger cats need 100+. I am guessing you are shooting a massive rooster tail to be slipping that much. Sorry, I can only think the setup such as drive height / props is far off the mark. How much does the boat weigh?
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Old 08-07-2002, 12:16 PM
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First things first, get some rpm's going, and see what the gps says, keep in mind, you are safe in a straight line in a cat, it's when you turn that things can happen, so take it slow, get some speed up in a straight line, and re-evaluate prop selection, and trim if those drives are trimable, but most importantly, have fun, and get us a bunch of pictures. You gotta get the hull in the zone, or get some lift on the hull to let it come alive, plowing at 45mph is no fun in a cat! is it on plane at 45?
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Old 08-07-2002, 01:13 PM
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The boat weighs about 8000lbs.I have tried bigger props but the 26x15.75 works the best.Anything bigger and I can barely get on plane.The boat is on plane at 45.I do run the drives pretty high on the trim indicator and I am shooting a rooster tail.Maybe I should have the drives down more.I am going to go to 5000rpm this weekend and see what happens.I have the rev limiters at 6000 and I am sure I can hit them .I am sure that I have some work to do with the trim.The Kaamas are trimable.The problem is with the surface drives you have to get the props to cavitate and then it will hook up,no hole shots with these drives.I also think that I am scrubbing speeds because I think one of the drives is towed out a little.I am having trouble trying to find a place to measure them so they are perfectly straight behind the boat.I also need to adjust the trim to make sure they are both the same as the guage reads.Also sometimes it starts to wander but not out of control.This is a true tunnel without a center pod.On the inside of each sponson there is a shaped piece of wood about 18feet long and 2"wide that is curved on the bottom.They are pretty chewed up.Does anybody know what they are for?I am sure they must be for lift or something.I will have to find a wood working shop to make new ones.Keep the info comming.
Mark
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Old 08-07-2002, 01:46 PM
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just an idea .....go to the top of your post here and click edit ,Then in the top subject line where you put "Running a cat " Add " with kaamas" or something to that nature . These kaama guys need to a little slap to get them going and talking . Once you get their attention ,you'll get the info you need !
That ,and that guy that talks too much ! "TxYz3" or something like that . . Once he gets up from his nap ,I'm sure he'll have something to say worth carving in stone !

The only down side I see with small blocks is very little torque on the low end .That would be your problem getting on plane with bigger props that you probably need .Once you wind them up ,they make the hp . but it's mostly top end . Nothing a couple small blowers wouldn't help !
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Old 08-07-2002, 02:19 PM
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I think part of the key might be the small blocks. 8,000 lbs is ALOT of weight-especially for a cat! Even though your small motors are making good power, they don't have the torque that it's going to take to move this thing. I'd have to guess that they won't have enough power to really start lifting the hull out of the water.
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Old 08-07-2002, 02:37 PM
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Quote:
Originally posted by fishead
.The boat is on plane at 45.I ........

On the inside of each sponson there is a shaped piece of wood about 18feet long and 2"wide that is curved on the bottom.They are pretty chewed up.Does anybody know what they are for?I am sure they must be for lift or something.I will have to find a wood working shop to make new ones.Keep the info comming.
Mark
I was just kidding about the on plane thing. The shaped piece of wood thing, is this like a spray rail like most cat's have? They usually follow the bottom, a few inches above the running surface in the tunnel, and are a few inches wide, and fade out into the tunnel as you get towards the front. We may need some pictures here. Made of wood, is the entire boat made of wood or fiberglass, or is the wood piece looking like someone added it on after it was produced origionally, to possibly try to improve lift? I'm definitely no expert with surface drives, I run outboards on my cat, but with a high x-dimention, and they cavitate and need to be worked on plane, but this wandering you are talking about, it may be part of the tow in/out one may be off?? I dont know the Kamma's setup, or adjustability, rudder, non rudder? I dont know, but measiring from the centerline of the rearwardmost part of the propshaft, and the centerline of the middle of the drive where it enters the transom should give you a starating point one way or another, just keep filling in the blanks for us and lets get some Kamma experienced people asking the right questions, and see if we cant get you where you want to be.
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Old 08-07-2002, 02:47 PM
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This boat was en ex APBA race boat in the late 80's early 90's called CAT DANCER.I called Michael Peters the designer and he said he designed that boat to run small blocks and it will run in the upper 70's low 80's with my power.The boat is glass and the wood pieces may be spray rails.I am going to call Michael Peters again and see if he designed them there or they were an add on.The power plants will spin the 26"props all the way to 6krpm,at 4krpm I have alot of throttle left, so I do not think that is the problem.That is a pretty big pitch,bigger than some race boats.Keep the info comming.
Thanks
Mark
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