Power calculations
The wind turbine outputs 250Watts peak so will output the following: 250W/12V = 20.83Amps (Turbine output - peak).
If you had a standard 100Ah battery in your yacht, the Rutland 913 wind generator would have it charged, from flat, in around: 100Ah x 80% = 80Ah, 80Ah/20.83Amps = 4 Hours minimum.
As the turbine wouldn't be on peak all of the time, 4 hours charging is the best case scenario. Due to the unpredictable nature of renewable energy you could usually expect to charge your marine battery in about 16 hours.