I will ask a question for sailors here and add a bit more detail on actual sailing.

You may have missed my point that motoring to charge a battery will rob more distance covered than you can recover by motoring.  If you have a nice breeze and are humming along at 8 to 10knots toward your destination there will be some reluctance to drop speed to 4 or 5kts for a few hours to charge the batteries.  You may start out with a different view but reality is a tough master; mid afternoon 20nm from a safe port with a busy shipping channel and no sun charging batteries, batteries down to 30% after two days of little sunshine with wind rising and channel current due to start ebb at 6pm and peak at 5kts at 7pm - what do you do.   I would like the choice to either run a small generator to get the batteries up to capacity before entering the channel but keep sailing at best speed or be prepared to run the diesel propulsion upon entering the channel.  It may work out that the wind is just right to allow you to sail though the channel but you need to be prepared for adverse conditions.  

A sailing boat spends approximately 50% of the time going up wind if it is an efficient upwind performer like a HP; longer if inefficient unless motor-sailing.  That is simply a factor of the windward VMG versus the offwind speed.  I have seen some bilge keel heavy cruisers that tack through 160 degrees in good conditions and simply go sideways if there are decent waves.  Upwind performance is a function of overall sailing efficiency.  Charging a battery upwind using an electric drive as a water turbine will reduce the overall sailing efficiency on a HP to the point where the VMG is a negative number.  So regenerative sailing is really out of the question for 50% of the time when sailing. Although I have not assessed this quantitatively, I have a reliable VPP for HPs and could advise the loss in VMG versus the rate of battery charge.  We do not try to sail the 18m proa with the drives immersed because  just the drag on the legs and free spinning props kills sailing performance.  The drives swing sideways using 2X lifting tackle and the one that the torque is pulling away from the lift is impossible to lift when speed is above 8kts because there is insufficient strength to overcome the torque, even without regenerating.  As soon as sails are up and the boat is moving the drives are lifted clear of the water.

Rick

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