You get into the anchorage near sundown, and it needs a considerable amount of power to do so (against the tide and/or wind, along a narrow un-sailable passage). You want to get out in the morning, and will need plenty of power again. A petrol genset will disturb the overnight peace. Then, wind is the only option available
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Well the most recent turbine I had, which burnt out at the end of January in Storm Brendan, would have contributed approxiamately zero amp-hours to the batteries overnight in such a scenario. Any anchorage worth anchoring in will hopefully not be blowing a steady force 6 or 7 which is needed for these little gennies to crank any useful power out. In fact, and it's a current best-selling model, it's controller actually uses more power than the turbine creates for most of the time.
You do see them quite often on cruising boats but one wonders if the owners are delighted with them, most I've talked to are not.
There are plenty of Airbreezes, etc, to be seen on long-term, long-distance, high-electricity-usage cruising boats. Myself, I prefer the total silence of solar panels, but if I were to go for electric propulsion, I can only see it as being safe and dependable if there were as many sources of generation as feasible. Hydrogeneration is certainly one of them in certain circumstances
I agree, many sources is good insurance. It might also be worth considering a bio-ethanol fuel cell like the Efoy... (might be opening a new can of worms discussing that though!)