Dynamo hubs?

[02gf74]

... and if it is overcast, you can shine a torch onto the panel.

 

[xerxes]

Re:

.. I imagine that will work every bit as well as putting a fan at the back of a sailing boat.

 

[02gf74]

Re: Re:

.. I imagine that will work every bit as well as putting a fan at the back of a sailing boat.

No it will work much better.

The above won't work - remember Newton's third law - there will be an equal force pushing back on the fan. Assuming the fan is fixed to the boat, which is has to be else it will drop off, the fan will push the boat back so nett forward motion is cancelled.