head of the river cat hull thread

[ozzie-crawl]

hi paul. it it will flip on fast cornering but if i slow down then turn and excelerate it will spin out. from what i see if the nose is a little to high then it spins out if the hull is running to flat it flips. iam having trouble with mine at the moment just to get it running nice in a staight line if i run the hull a bit wet it is very twitchy at speed, if i run it nose up it becomes very loose and spins out easy may have to drop the prop size back down
cheers scott

[DISAR]

I have the same boat but not "pushed" it too much until now. Seems that the boat has a speed limit for proper handling. If you compare it to a Mean Machine for example this is much narrower which means less stability.

[Jeff Wohlt]

You need a pretty deep rudder...and wider....a typical Fuller rudder is not enough because it is not wide enough. The MM rudder (speed master) is wide and deep. Too big of prop can also cause problems in corners.

I am running a wide tappered style and will let you know when I get to run it.

Yes, the narrowness of it can be tough. Be sure everything is as low as you can get it...no cells on top of the tub, etc. Cells should always be in the sponsons for best perfromance. Prop can have decent Dia but watch the pitch. I figure a 442-445 with mine to start.

[Jeff Wohlt]

Still working on this but hardware is done. Running 078 wire (062 is in it now and might try it to see how it holds the power)

5/32 Stuffing tube and very smooth. The rest is homemade...motor mount, etc.

Will run 4S, 8Xl, Etti 150 ESC and starting with 438 prop...Paint...not sure but I am considering trying my buddy's wrap system...says he can do anything I want.

[785boats]

Looking good Jeff.
It will be good to see how it handles.

For what it's worth,a guy turned up last weekend (didn't catch his name unfortunately) who used to race fullsize tunnels & cats. He told us what he thought the problem was after only watching two laps & three spins.
He said that as I come off the throttle going into the turn the hull doesn't just drop the nose, it rocks on the air under the hull. That is to say that the nose drops but the tail lifts. Giving the hull a slight nose down attitude. This makes the chine of the outside sponson grab at the front & it lets air in under the side of the rear of the sponson as it starts to turn. So the rear slides out as it pivots on the front edge of the outside sponson. This causes the spin out. The fullsize ones can have the same problem.
The remedy is a small turn fin at the very rear of the inside sponson, according to this learned gentleman.
I know the purists will say that a cat does not need turn fins, but it's worth a try. I'll knock one up & try it out this weekend.
All the best.
Paul.

[Jeff Wohlt]

I have thought of that on some past hulls. Just a small tab maybe 1/2" in the water or so and inline with the inside sponsons could make a big diff.

As you can see, I am running a pretty deep rudder and steps on cats can be tricky with the CG to get some cornering.

Maybe you just don't let off the throttle in the turns :)

[calcagno45]

Could the CG be a little to far forward? Might slide it back a hair and try that.

Also, what about a skeg on the strut? Like:
http://www.offshoreelectrics.com/pro...rod=oct-struts

Just a little more to help keep her straight...

[ozzie-crawl]

hi paul. got a chance to play with the cat on the weekend for some testing. my c.o.g was to far forward so after fixing this and reseting the strut angle the boat is running very nice. i was having trouble with interferance for awhile (under ground pumping system) but i did get to try some cornering out and what i found was to back of a bit at the start of the turn and once you are about 1/3 -1/2 way through excellerate hard out of the turn. tryed with a smaller prop. x440 it was running 88klmh (55mph) was only pulling 68 amps max and temps were low,would like to try a x442-x445 prop but dont have one so going to try a detounged x642 this weekend
cheers scott

[Gerwin Brommer]

I shouldn't have sold mine

[785boats]

Well guys, Thanks for all the great info & help .
Yesterday I finally got the cat to take the bends at 3/4 pace. At top speed the arc is just too wide for the course.
On all your advice I've done the following.
Dropped the strut a smige, added a small hooked turn fin on the rear of the right side sponson, & changed back to the X642 prop.
Still moving the COG around a bit each run.
I also decided to remove the wedge from the tunnel to reduce the lift.
for next weekend I'll add a bit more throw to the rudder linkage. If that doesn't tighten the turn without hooking again it looks like a wider blade may be needed as you suggested Jeff.
But man, am I happy or what?
Thanks again to you all.
Paul.

[Jeff Wohlt]

A skeg on the cat strut works well on cats. It stops the dancing when WFO down the straights.

[ozzie-crawl]

hi paul good to hear your getting it sorted. how many of you running the cats up there now.
jeff can you please explain about the skeg and if possable a picture
cheers scott

[Jeff Wohlt]

Here is one shot but I think Speedmaster makes some. This one is a mini but gives you an idea. (on the left) It is really just another part that keeps it running straighter. All lower units have them in real boats and is known as the skeg.

[785boats]

I'm happy with the way the cat runs in a straight line. No wobbles or twitches, no skipping or bouncing. Just straight & fast. But I'll keep the skeg idea in mind.
Scott. There's about 4 of them in the club now & a couple of Blackjacks.
See ya next time you're up this way.
Paul.

[ozzie-crawl]

thanks jeff. i thought that was what a skeg is but didnt even think of adding one think i will try it.
4 thats good geoff and i will have to come up soon. just waiting to get some batteries.
cheers scott