Slow build - 8S Twin Cat

[TRUCKPULL]

OK guys I have got to have a better idea about the CG.
Once I glue down the ESC trays, I will be restricted to how much I can move my batteries, to adjust the CG.

Larry

[jaike5]

Don't use battery trays. velcro on the floor with small tab of velcro on each end of the batteries , wedge a pool noodle between the deck and the batteries and they stay put. lots of room for adjustment, great for windy days and ruff water.
J.

[TRUCKPULL]

Jay -I do that with my 6S twin Cat, But I have had a battery unplug in a flip and stuff.
The batteries in this one are heaver, so I would like them to be anchored a little better.
I am asking about the ESC trays, Once I glue them in, I will only have about 1 1/2" of movement in the Batteries
because of the short wires on the ESC's

Right now The best I can get is 13 1/4" to 14 1/2" from the transom

This why I am asking about the CG on a large CAT.

Larry

[fweasel]

I measure my CoG from tips to the rear of the ride pads and start at 30%. Your long drives and rudder arm are definitely going to add more stability, but that hull looks wide and tall. I suspect it's going to pack a lot of air. I end up running my long skinny hulls way over 30% (HPR, Genesis, Rivercat) to keep them on the water at SAW speeds. The 48" Zelos G I converted to electric, was a wide, tall hull. It packed a lot of air and I just couldn't keep it glued to the water after a certain speed threshold was passed. I was worried I was starting with my CoG too far forward in that hull. Painted myself in a corner, and had to run the two 6S packs pushed all the way back just to hit 33ish %. I ended up pushing them farther forwards every pass as I figured out how the hull responded to the power I was throwing at it.

If you're copying a tried and true setup, glueing everything in makes sense before testing. When you're blazing your own trail, I'd leave as much adjustment as possible before the initial runs start. Skip the battery trays until you know what you want. Since the ESC wires are a limiting factor, I'd also hold the ESC's down with some type of temporary fashion, couple dabs of aquarium silicone or something like that. Lots of foam on top to cushion them if they let loose in a blowover. It really won't take much time on the water to quickly sort out where you need to be weight wise.

[TRUCKPULL]

I measure my CoG from tips to the rear of the ride pads and start at 30%. Your long drives and rudder arm are definitely going to add more stability, but that hull looks wide and tall. I suspect it's going to pack a lot of air. I end up running my long skinny hulls way over 30% (HPR, Genesis, Rivercat) to keep them on the water at SAW speeds. The 48" Zelos G I converted to electric, was a wide, tall hull. It packed a lot of air and I just couldn't keep it glued to the water after a certain speed threshold was passed. I was worried I was starting with my CoG too far forward in that hull. Painted myself in a corner, and had to run the two 6S packs pushed all the way back just to hit 33ish %. I ended up pushing them farther forwards every pass as I figured out how the hull responded to the power I was throwing at it.

If you're copying a tried and true setup, gluing everything in makes sense before testing. When you're blazing your own trail, I'd leave as much adjustment as possible before the initial runs start. Skip the battery trays until you know what you want. Since the ESC wires are a limiting factor, I'd also hold the ESC's down with some type of temporary fashion, couple dabs of aquarium silicone or something like that. Lots of foam on top to cushion them if they let loose in a blow-over. It really won't take much time on the water to quickly sort out where you need to be weight wise.

Ryan
That sounds like a plan, I can live with.
13 1/4" is 32%
14 1/2" is 35%

Larry

[srislash]

Keep the weight back Larry. I am pretty sure I?m 30-32% on my R42. These bigger hills do pack the air but won?t likely be much over 70 and they are heavy with packs and gear. One usually wants to run it as light on the water as you can. Bigger gas hills are usually designed to run wet because then they stay glued into the water in a race situation.

[jaike5]

Only one battery came un plugged thats pretty darn good on a 60plus mph flip. Batteries in the sponsons lower cog and spread the weight. My insane G3, 10s 2p
44" hull is right at 30%.
J.

[Jesse J]

I agree with Ryan on 30% start cog. In new to me boats, I like 2-3% wiggle room forward and aft.
Desired application, speed, hull design (lift) and other factors play into the equation.
Agreed lighter is better, but ultimately handling at desired speed is the most important. I am not against a little ballast if I just can’t arrive at the correct cog. I’m sure some will cringe at the thought of adding even more weight.. not first option, but not the end of the world.
On the other hand, if you just cannot get cog far enough forward, one can add a small air dam to reduce lift.

Ideally, layout should allow 2-3% around the target 30%.

[TRUCKPULL]

Thank You very much guy's

So it looks like my next project is all the wiring
water pumps, Servos, ESC's, BEC, Radio.

Then Paint

Larry

[TRUCKPULL]

I have figured out a way to get the CG down below 30%
This is a rabbit hole that I don't want to go down.
So hopefully my set up at 32% turns out OK at testing time.


Larry

[ray schrauwen]

Just keep cranking the props down, lol.

[TRUCKPULL]

Just keep cranking the props down, lol.

My setup right now is 3 3/4 degrees down. This should be a good starting point seeing my Q is at 2 1/2.

Larry

[Doby]

Started the cg on mine at about 30%.

Running mine on 10S2P with a big Neu 2215 in it.

Just got it tuned in at the last Michigan race I went to..its a beast, heavy as a tank, but moves nicely.

Went with dual rudders on mine.20220127_003702.jpg20220127_003713.jpg

[Doby]

.....another pic...fbcat.jpg

Think this was taken in London...Chris K's cat in the background.

[Jesse J]

It’s all about the upright fins, that’s why you are ahead!
Great looking boat and I love the action shot!