We have a ROV robot that operates at 24 volts and with direct input power (No battery)
The cable used is 50 meters
Power consumption 1000 watts
35 Amp used
What cable number should we buy? (AWG)
Depends on your input voltage. If your input voltage is 24 volts and your tether is 10AWG, you will get less than 12V at the vehicle under load. Powering a vehicle from the surface is dangerous, and it is not easy. I recommend you use a battery instead.