48" Catamaran build, looking for criticism before I buy

[Quax]

I'm building a 48" Catamaran with the goal of running 5 miles at between 45-55 knots. From reading forum posts and guides over the past months, I've come close to a list of parts. I'm looking for criticism and pointers, specifically about the motor, but I'll take anything you've got.
Here's the parts list:

• 2 780kv Leopard 56110 motors
• 2 6s 20Ah LiPo in series
• 2 Turnigy 150A ESCs

I'm running the motors/ESCs in parallel, and I expect prop diameter will be upwards of 56mm.

Thanks in advance

[srislash]

Which hull are you building? I?m thinking 56mm motors may not be necessary.

Mmm, on second thought 20,000mah won?t be light.

[Peter A]

From my experience with running endurance I would go with a much lower kv, like 500kv, you can prop to suit. In a 45" mono with a TP 4070 440 kv it will do 20 min runs at around 70 kph on 20 AH. The high capacity batteries are all low C rating so you need to be careful of amp draws on them. Based on the speed and distance you are looking at 12 min runtime, with a max average amp draw of 80A. I am not sure you proposed setup can draw that low amps for the speed you are after.
Are you actually racing over the 5 miles or just running alongside a boat or such like? At the speeds you want to run at, on open water stuffing in at speed is very possible.

[Quax]

Wow, that was fast.

I'm new to this, so I don't know what "stuffing in" means. I'm running a 1-mile track in a creek just outside the Chesapeake Bay. There'll be a boat to fish it out if something goes wrong.

Do you know what kinds of considerations you need to make when building a twin-motor vs a single-motor design? Are props and motors going to be smaller with a higher kv?
Is there a significant difference between a 40mm and 56mm motor with the same kv?

[Peter A]

I think you may be better off with 40mm x 100 mm cans. They will give you the torque you need. I run an ABC 2414/4 chopper on my 45" mono for speeds around 80 kph. That would give me aprrox a two mile run on 12s 6000 mah, on an oval course (11 laps). The higher the kv, the smaller the props. Lower kv and bigger props would be my preference. With twins, the motors 'help' each other so the individual load is less on each motor. The smaller cans will be easier to mount also, whether you are mounting them on the tunnel or in the sponsons. It all depends on where your batts will fit really.
Stuffing in, is when the boat pretty much trips on the water and goes in nose first and hard. You need to reinforce the hull for the weight and speed. CG balance will be fairly critical at speed also.

[hispeed10k]

I think you may be better off with 40mm x 100 mm cans. They will give you the torque you need. I run an ABC 2414/4 chopper on my 45" mono for speeds around 80 kph. That would give me aprrox a two mile run on 12s 6000 mah, on an oval course (11 laps). The higher the kv, the smaller the props. Lower kv and bigger props would be my preference. With twins, the motors 'help' each other so the individual load is less on each motor. The smaller cans will be easier to mount also, whether you are mounting them on the tunnel or in the sponsons. It all depends on where your batts will fit really.
Stuffing in, is when the boat pretty much trips on the water and goes in nose first and hard. You need to reinforce the hull for the weight and speed. CG balance will be fairly critical at speed also.

What size can do you run in your 45 mono and why? That’s next holiday project build. Thanks!

[Peter A]

What size can do you run in your 45 mono and why? That’s next holiday project build. Thanks!

I have been running a TP 4070 440kv on a Seaking HV 130 esc. This was an endurance setup, but due to too much bs and the cost of batteries I stopped doing the endurance. just sticking with club racing.
I have just decided to upgrade it to a Castle 2028 and SF300 esc that I have for next years race season.