Cheetah xl - hull problem??

[MikeP323]

After looking at it for weeks I bought the last Cheetah XL that OSE had listed. It was on there so long I thought it needed a home. It is set up with two TP 1750 KV motors fed by a couple of ZTW 200 Amp ESCs. The rudder is the original blade except it is hung out back on a six inch extension. This stopped the hooking it was doing with the original bracket right against the transom. The present set of props are 1814 ABC by DasBoata. I am running 6S to each side.

The problem is that that boat will lift occasionally and run like it should with the bow up and it flies. Then the bow will drop and it plows and really does not want to come up but it will for a bit and so it goes up and down. I have never done the bottom of a boat but put it on a flat and saw that one side was not quite touching by maybe 1/32 in. A friend who has done this work before leveled one side and now the space is gone and all seems square. This operation did cause less plowing but it still drops often enough that I feel it is a problem. I have added about three ounces of weight back at the transom and run the batteries and ESCs as far back as I can. Both stingers are raised about one degree.

Is there a tutorial some where that would give me some basic info on leveling the boat bottom if in fact that is the problem. What materials to use and the steps etc. I know all edges need to be sharp but thats it. Do the three bladed props have too much lift. What props should I consider? HELP!! And my thanks to all who read all of this!

[koen]

Do you have the CG wright ? because it's very important ,you can move the batteries to front and aft to get the cg wright and try to raise the stingers a bit more ,to find a good setup take some time

[larryrose11]

First step I would think is to blueprint the hull.
Did they correct the design problem in the new version? Here is what I did on my original Cheettah:
https://forums.offshoreelectrics.com...636#post518636

This blueprinting process should let you run a level stinger.

[MikeP323]

Koen Thanks for your reply - I do believe I have the CG right using about 33% of the hull length as a start and experimenting from there on my smaller (34 inch) version which is running really well. This one that I am having trouble with is the XL version
39 3/4 inches long. The only way it will come on plane at all is with the batteries as far back as I can get them. I will try raising the stingers a bit more but I believe the whole bottom needs to be blueprinted.

[jkflow]

What motor / prop combo do you have on your original non XL? Struggling with heat myself.
Sorry for side-tracking.

[MikeP323]

larryrose my thanks for your reply. After looking at the photos of your blueprinting process I can safely say that I would need some instruction before I attempt that operation. I might try and level a few more of the pockets using epoxy and balloons though.
I also looked at the pic of Tiumans hull and mine does have that problem with the last step to a lesser degree I think. It also has some low places that need to be filled. I think I have been told that body putty has been used for as filler for the process by some - I wonder if there is a downside to that. It sure would sand easier but is it durable?

[MikeP323]

jkflow - I am running two TP 4050 2100 KV with CNC 5016 2 blade detongued props at this time - It has been very successful in club racing but since I live down South it does run a bit hot however not to the point of any failures yet.

[EddieM41]

jkflow - I am running two TP 4050 2100 KV with CNC 5016 props at this time - It has been very successful in club racing but since I live down South it does run a bit hot however not to the point of any failures yet.

Must be 4S with those motors! Otherwise, it would burn down (I speak from experience).

[larryrose11]

larryrose my thanks for your reply. After looking at the photos of your blueprinting process I can safely say that I would need some instruction before I attempt that operation. I might try and level a few more of the pockets using epoxy and balloons though.
I also looked at the pic of Tiumans hull and mine does have that problem with the last step to a lesser degree I think. It also has some low places that need to be filled. I think I have been told that body putty has been used for as filler for the process by some - I wonder if there is a downside to that. It sure would sand easier but is it durable?

Lots of info on this site about blue printing hulls

just get some microbaloon so mix into a lowish viscosity, slow set epoxy. you can mix enough in that is can become like mashed potatoes, or make a dam to prevent it from running. Boat sealing tape works well to make dams, but must be applied thoroughly while everything is clean and dry.
You will be WAY happier with the result.
Bonndo sux, and gums up when you try to sand it. Clogs the sand paper.
Aside, always use slow set epoxy if you can. Its stronger. Fast cure epoxy can not be waterproof too.
You can speed up the curing process with an incandescent light to increase the temp, but don't go over 130F

[MikeP323]

Must be 4S with those motors! Otherwise, it would burn down (I speak from experience).

True - the boat was built to run using 4S as it is run in "P" or what we call "Straight P " in our club racing. I do know about burning things up and down and it is NO FUN! I have run it on 5S occasionally with no problems other than how to hang on to it.
It was pretty quick.

[Alfa Spirit]

I think it’s a design problem, the catamaran is wide so it’s very sensitive to the tunnel effect. As soon as a flip is triggered it’s screwed. The choice is to adjust the center of gravity further forward or to change cat...

[MikeP323]

I think it?s a design problem, the catamaran is wide so it?s very sensitive to the tunnel effect. As soon as a flip is triggered it?s screwed. The choice is to adjust the center of gravity further forward or to change cat...

ALFA - Flipping has not been the problem. The boat is doing the opposite - it is plowing a lot and only lifting occasionally and then flopping down to plow some more without letting off on the throttle . Since I have more than a grand
into the thing I believe I will work with it some more before changing. The boat does need to be blueprinted. I am still looking for a tutorial on how to do that. I will probably try the method larryrose suggested (see below)
Thanks for your reply.

[Silver954]

I'd move some weight to the rear slightly and see if it helps. Also you can try different props with slight tongue/lift to see if that changes the ride attitude.

[MikeP323]

I'd move some weight to the rear slightly and see if it helps. Also you can try different props with slight tongue/lift to see if that changes the ride attitude.

SILVER - thanks for your reply. I have a few other sets of props and plan to give them a try. I have about five ounces of sticky weight back at the transom. I was told to try running with one battery back and the other forward. Well with the right forward and the left aft it got its nose up and stayed up until it flew thru the air with the greatest of ease It was really moving . I am presently strengthening both sides with zpoxy and fiberglass as the hull flexed. TFL built this thing with no carbon fiber inlay so I should have done some work on that first.

[Silver954]

You are on the right path to find the right CG for the cheetah xl. Since it's a longer hull it will need that center of gravity slightly further back than the regular cheetah. I think you were pretty close so small changes should do it.