Given Robs tender motor reuse for boat motoring, I was wondering if an electric tender made sense, as the tender should not need a long power duration.

Then I was wondering if dragging the prop might be a redundant/additional power source. Given swapping the prop out for one optimized for 'dragging', does this idea have any merit?

    Many DC brush motors can be made to generate........ I've made generators out of motors in the past, and vice versa.   Ideally one would have a shunt wound motor versus series.   Shunt wound motors have less torque, but are more efficient, and easier to regulate.    An automotive electric starter is series wound....... designed for extreme torque for short intervals.  I would suspect that most outboards are either shunt wound or pemanent magnet, either of which could generate easily with some creative modification.   More and more we are seeing brushless DC, and these would seem completely unsuited, though one of the two types could be built from the factory to generate I suspect.   

    It's far from an original idea, and you will find a number of discussions on this topic by Googling.   The fact that the manufacturers of electric outboards do not offer this feature.... which is a pretty obvious value added feature, suggest to me that it simply does not work well.    In general a motor will work well for motoring, and less well for generating.    The newest generation of high efficiency electric outboards are probably completely unsuited for this.... at least that would be my guess.........

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