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.

[Mike W]

The hull running surfaces are concave front-to-rear. A massive amount of work is required to correct this. Put a straightedge on it and you will see the center two running surfaces lower than front and rear. The concave portion causes it to stick to the water anytime the nose drops even slightly.

[Silver954]

If you post pictures it will help visualize what you are saying

[Mike W]

Set it on any flat surface. Observe where the hull contacts the table at the end of each running surface. There are 4 on each side. All 8 should touch the table at the same time. On every hull I?ve seen the middle two on each side are high. I think the hulls warp. You could try a bulkhead? Always check for twist too.

[MikeP323]

Set it on any flat surface. Observe where the hull contacts the table at the end of each running surface. There are 4 on each side. All 8 should touch the table at the same time. On every hull I?ve seen the middle two on each side are high. I think the hulls warp. You could try a bulkhead? Always check for twist too.

Mike - Is this a problem with all Cheetahs or just the XL in particular? Then u mentioned trying a bulkhead which I am not familiar with either. I am still fighting the battle with this hull which has been blueprinted by a friend with no tangible results. Thanks for your reply!

[Mike W]

Just the XL. And possibly also because of the additional step that no other cat I have ever seen has. The bulkhead comment was a suggestion to possibly stiffen the low area to the deck to make the repair more stable.

In most cases blueprinting is smoothing the existing running surfaces to flat and squaring edges. If they are not true to start with there is a great deal more work that needs to be done.

Have you placed it on a flat countertop to observe how true the running surfaces are?

[MikeP323]

Just the XL. And possibly also because of the additional step that no other cat I have ever seen has. The bulkhead comment was a suggestion to possibly stiffen the low area to the deck to make the repair more stable.

In most cases blueprinting is smoothing the existing running surfaces to flat and squaring edges. If they are not true to start with there is a great deal more work that needs to be done.

Have you placed it on a flat countertop to observe how true the running surfaces are?

Yes I have and it still needs more work on the bottom thats for sure. I did find that one of the two motors was faster by 1744 rpm (no load) and so they are now matched with a new one to match the other new one already installed. (within 10 Kv.} Funny that the installed used motor had a higher Kv rating than the new one. I dont know if the matchup will help but it cant hurt. As to the bottom I believe I will need an expert in the booth with me.

Thank you for your reply! MAP

[Notoriousone]

Just guessing here, but you mentioned that you adjusted the struts up a degree, maybe try 1 more degree up? Are you using lifting props? If so, maybe some non lifting props and a slight upward strut adjustment would help to get the bow up. I also think large fiberglass RC boats can come out of the mold straight, but then slowly warp especially if there is no Carbon or Kevlar lining

[MikeP323]

Just guessing here, but you mentioned that you adjusted the struts up a degree, maybe try 1 more degree up? Are you using lifting props? If so, maybe some non lifting props and a slight upward strut adjustment would help to get the bow up. I also think large fiberglass RC boats can come out of the mold straight, but then slowly warp especially if there is no Carbon or Kevlar lining

Thanks for your reply Notorious. Yes I have tried the struts at all reasonable angles. Now to lifting props. I have tried ABC three blades and detounged CNC two blades to no avail. What type props make the least lift? I am about to try a small aluminum blade at the nose to give it the bit more it needs to get up and stay up. I have used blades to put some downforce on cats but this will be the opposite. Have to drive it with the throttle then for sure I think. When it does get up it flies.

[Silver954]

Big cats handle like a drunk noodle at low speed. They have to be on top of the water going to act normal.

[srislash]

A set of Octura 447’s should be a good all around choice here. Low on the lift. This is my go to on my R42 cat which is similar in design, ( ie: wide body). The ABC props you have, are they SK series? If not then most other ABC props are of high lift. They SK series will actually push the nose up (or push transom down depending how you look at it). What you seem to be experiencing is the old Geico hop or porpoising. It is a combination of small things to get past this.
You may also be onto something with ‘the blade’ in front of tunnel. The tunnel design can also effect things.
Have you tried an air dam under the tunnel? This is commonly done with a windshield wiper blade taped to the underside of tunnel a couple inches back from the leading edge of the tunnel. This will create turbulence within the tunnel and sometimes helps.
Aerodynamics comes into play on anything over 35mph so on our light little boats doing 50-60+ just imagine.

Just sharing thought# and experience here, Shawn

[JOHN BOCCHER]

Hello every body, I am looking for some expert advice for those of you you that have a lot of experience with the TFL cheetah XL . I am about to give up on this hull if I can't get it fixed over the winter months.
First a little history. I bought the Cheetah directly from TFL . To run in our club under Q cat Club and IMPBA rules which are as follows. Max hull length of 40 inches . The hull just makes that rule as my hull is 39.75 inches. I must use a 40 mm x 92 mm single motor and run on 6s Lipo battery. and limited to a 50 mm prop. TFL now sells this version with a SSS 40 x 92 mm 2140 kv motor. So I originally went with that.For added strength they added the Kevlar to the hull with water pick ups in the bottom rear sponson. When the hull arrived they had the battery trays mounted as far forward as possible in the hull. I have already moved them back but not enough yet.I was burning up 200 amp ESC. It was suggested that I switch motors to a TP 40 mm x 92 mm and a 1350 kv and use a Castle XLX2 manba hydra 180 amp ESC. I have tried up to a 445 prop with the flat bottom strut up 1/8 inch from the bottom of the sponson. The hull runs very very wet and only hit 41 mph.
I can only get to boat to balance at 13 inches forward of the transom.
I am now in the process of moving the battery trays back as far as I can . I could get another 1 1/2 inches further back if I remove the dual bottom sponsom water pick ups and just stay with my dual water pick up rudder. With the Castle ESC relocated toward the rear behind the motor it would just fit between the shaft tube and the servo radio tray. This will allow me to get the GG back to 11 1/2 inches forward of the transom.
If I remove the bottom water pick ups I could gain another 1 1/2 of battery movement to the rear if need be. This hull weighs in at 12.5 lbs. ready to run.
After ready many post here on the design flow of the sponsoms, I check mine and they are off big time. I can see why the bot is stuck to the water.
So, I guess from here what would the best motor kv be if I stay with my new castle ESC ,or am I looking at another new larger amp ESC. ?
What would be the best CG location for the configuration. ?
Also should I install a rudder extension to move the rudder back off the transom ?
I need to find the site with pictures that shows me what the corrected sponsons look like.
Thank you all for any help you can give me in advance.
Signed frustrated .

[Bande1]

post a pic of your data log

[koen]

maybe this helps:set the strut 1/8" above the sponsons and if you need lift at the front use ABC 1815-17 this prop you can use it for a start and put the battery try's next to the motor(the motor you use is exellent)and also you can give the strut up angle (just a bit and adjust when need)

[srislash]

Hello every body, I am looking for some expert advice for those of you you that have a lot of experience with the TFL cheetah XL . I am about to give up on this hull if I can't get it fixed over the winter months.
First a little history. I bought the Cheetah directly from TFL . To run in our club under Q cat Club and IMPBA rules which are as follows. Max hull length of 40 inches . The hull just makes that rule as my hull is 39.75 inches. I must use a 40 mm x 92 mm single motor and run on 6s Lipo battery. and limited to a 50 mm prop. TFL now sells this version with a SSS 40 x 92 mm 2140 kv motor. So I originally went with that.For added strength they added the Kevlar to the hull with water pick ups in the bottom rear sponson. When the hull arrived they had the battery trays mounted as far forward as possible in the hull. I have already moved them back but not enough yet.I was burning up 200 amp ESC. It was suggested that I switch motors to a TP 40 mm x 92 mm and a 1350 kv and use a Castle XLX2 manba hydra 180 amp ESC. I have tried up to a 445 prop with the flat bottom strut up 1/8 inch from the bottom of the sponson. The hull runs very very wet and only hit 41 mph.
I can only get to boat to balance at 13 inches forward of the transom.
I am now in the process of moving the battery trays back as far as I can . I could get another 1 1/2 inches further back if I remove the dual bottom sponsom water pick ups and just stay with my dual water pick up rudder. With the Castle ESC relocated toward the rear behind the motor it would just fit between the shaft tube and the servo radio tray. This will allow me to get the GG back to 11 1/2 inches forward of the transom.
If I remove the bottom water pick ups I could gain another 1 1/2 of battery movement to the rear if need be. This hull weighs in at 12.5 lbs. ready to run.
After ready many post here on the design flow of the sponsoms, I check mine and they are off big time. I can see why the bot is stuck to the water.
So, I guess from here what would the best motor kv be if I stay with my new castle ESC ,or am I looking at another new larger amp ESC. ?
What would be the best CG location for the configuration. ?
Also should I install a rudder extension to move the rudder back off the transom ?
I need to find the site with pictures that shows me what the corrected sponsons look like.
Thank you all for any help you can give me in advance.
Signed frustrated .

If your ride pads are convex at all it will run wet. They should be ?blueprinted?. They should be flat with a very slight dihedral(like 2-3degrees). Until this is checked or done you cannot make proper adjustments with consistency. As stated the ABC props will lift the nose.
Shawn

[JOHN BOCCHER]

post a pic of your data log

Hi Bande1,
I don't know how to do that but i can type the info you would like. I have found other problems with the bottom of the boat. They steps are all different . Two on the right side are low and the middle step on the left side low low by about an 1/8''. I need to fix them first.