M939 series had a new hydraulic winch, and separate numbers for with/without winch models.

The rear section houses the rear axle, hydraulic winch with 100 meters of cable, the operator and his/her controls, batteries, electronic control panel, and the drive gear.

As with any sailing race, the voyage must be completed under sail, and the boat must be operated and powered by wind and muscle-power alone (no electric or hydraulic winches).