genesis twin? Is the stock flex shaft to thin? calculate top speed

[waterproof]

Hi.

I maby want to buy a genesis twin version.
This is the setup:
2x 3660 2726kv motor
2x 120a esc
2x 36mm prop one is reverse.
Flex shaft is stock 4mm.

I wonder what the top speed is vs the single version with 3674 2070 motor and 38mm prop.
Both boats is stock out of the box from tfl.

Have reed about the speed calculator:
mph (Twin-Cat) = [prop pitch] x [Prop dia(mm)] x [kV] x [LiPo V] / 31060

This will give 49mph on 3s lipo on the twin model?
Would it be so fast or is something calculated wrong?

I have search around about the genesis and someone says that a stock single genesis could have trouble with the driveline even if it stock with 3674 motor 2070kv on 4s. Is that true?

Seems like the flex is 3,5mm on the round edge where it mounted to the motor and the other side is 4mm where it is square/ have 4 flat side?

Would the stock flex shafts be good enough if i buy the twin version and would it also handle a bigger prop or 4s?

It would be fun to try a twin motor cat, only had single motor cat before, im happy if it could reach 45-50mph :)

Only unsure about how mutch the flex shaft could handle before it snap and maby destroy the hull.

The next step is to buy a zonda with stock 4,76mm shafts but it cost more and it is a bigger boat, so big that i dont think it would fit back in the trunk of my car, that is why i maby go for the genesis and it cost me less :-)

Thanks for any reply

[10gauge]

My formula to calculate speed works for metal props, not plastic props. You'll have to have to deduct a few % due to the distortion of the prop under load. Here's the calculation of a 38mm METAL prop at 3S for a twin-Cat:

mph (twin-Cat) = [1.4] x [38] x [2075] x [11.1] / 31060 = 39 mph

However, 3S @ 23,000 rpm is not optimized for speed. Furthermore, a 38mm prop is too small for a large 37in hull, but only a starting point to get everything dialed in.

For me, I've never been hypnotized with twin drives. Prop factor (pitch x diameter) is the determining factor for speed, i.e. swing a larger prop, you're going faster. For me, twin-drives isn't the answer to substantially increase speed. The little gain in speed may not justify converting to twin drives - double cost, double problems, double complexity, more weight, but not double speed. But that's just me, others may disagree.

The hull could benefit from upgraded components:
- carbon center of hull reinforcement
- conversion to 0.187in flex cable assembly
- 0.187in Genesis strut (OSE stocks it)
- run it at 4S, not 3S
- m545, x445 prop would be the most I'd use for that motor with a 120A ESC.
- Can later change motor to TP4050, TP4060, or Neu 1521 AFTER reinforcing the hull and cable assembly.

Do prop and motor upgrades in small increments. i.e. don't jump from a 38mm prop to a 45mm prop.
Check temps after each mod.

BTW, I have a Genesis Offshore Cat on order too... It looks awesome!

[waterproof]

Hi. i mean 3s on the twin model since they have 2726kv motor, sure the single 2075 motor is a 4s boat :)

Dobble motor dobbel cost, dobble chance of trouble :p

I have only watch the twin model on youtube, seems like they go more straight forward and it's more stabile because of the two props, my experiance with single cats is that you get the torque roll/ hull is leaning to one of the side because the single prop on the middle and the torque.

Guess thats the same for all single cats, never run a genesis before but the single model also seems to handle a lot of speed without problem.

Good luck with your new boat. Very fun to try it for the first time :-)

I wonder how the 4mm shaft would handle the stock setup on both genesis model?
Could they also handle 4s on the twin model 2726kv or 5s on the single 2075kv?
I know it would be mutch rpm but i could also change motors to get the same power on less rpm if the driveline could handle it if i use it right :)

[Make-a-Wake]

If a Cat could ever benefit from twins it would certainly be the Narrow hulled Genesis.............torque roll is very evident with powerful single setups.

[martin]

Re the stock 4mm flexes, it will pay to have the extra head room going to 3/16" flexes. Having said that a friend ran the stock 4mm flex on a single Genesis with a 4082 1500kv on 6s for around 2 years with no flex failure before selling the boat.

[10gauge]

I wish you luck with your hull too. I'll probably run the stock motor and 4mm shaft with 4S2P/10000/25C packs until the bushings wear out.

Any motor mods might entail having to reinforce the hull. I've already ordered the Genesis 3/16" strut and a TP4060 4Y 1300kv for 6S2P - cart before the sea horse here. I ordered a weaved carbon sheet that I'll lay down with epoxy over the hull center.

As far as stability goes, I think the offset rudder will help avoid getting the rudder out of the propwash. I might experiment with the angle the rudder makes with the water, as a turn fin, to correct for any torque roll. I am sticking with a single drive. Ha, if the hull still won't behave well, it will make for a nice display in my office.

OSE is out of stock, does anyone know where to buy the Genesis Offset Bracket besides RC Boat Bitz (Australia)?...
Is stock cooling enough, or does one need additional water pick up?...

[martin]

Kintec Racing sells the offset bracket for the inline rudder.

[10gauge]

Thanks, Martin! I thought I'd get a double water pick up rudder too, just in case. I owe you a beer.