I agree with all comments, especially about getting a second source of charging the batteries, wether it be solar, wind, or some other. A lot of power can be shut off on a boat, but you always need you're Radio
, nav lights, and anchor lights, which have a way of bleeding the battery
dry at the most in-appropriate time. Make sure you have at least two batteries, which are isolated from each other, and can be run one at a time or together.
My experince with engines have all been deisel and found that the one cylinder 8 Hp ran at 1 litre /hr, while a 2 cylinder 18 Hp ran at 2 litres/hr. And Yes, plan on running the motor
for one & 1/2 hrs per 24 Hrs