Your math doesn't addup. Watts equals amps times volts.

Be nice to know the actual current draw of the winch under full load.
The battery charger with the 12 volt boost setting sounds like one
good answer. Spare battery sounds even better.

--

Christopher A. Young
You can't shout down a troll.
You have to starve them.
..

"Tom Kendrick" wrote in message
...
650 amps at 12 volts is 6500+1300=7800 watts of power, DC.
The rectifier (converting AC to DC) as well as a transformer (step
down from AC power voltage to 12 volts DC) will have some losses as
well. I believe that you will find such a rectifier to be impossibly
expensive for such an application. So costly that several alternatives
become affordable:
- Another battery, kept charged
- A small winch driven by a suitably geared gasoline engine
- A suitable tow line capable of attachment to a vehicle

There is no information regarding the anticipated current drawn by the
winch at stall speed, nor is the effective load of the boat (including
both friction drag and angle of incline on the railway).
Surely the winch does not demand maximum battery current along the
entire hauling path.