I have only played around with 12 volt ones that drew about 10 amps at slow - medium speed. = 120 watts. They say that a person in good condition can generate 50 - 150 MECHANICAL watts for and hour on a bike. The efficiency of your generator will be critical I would think, depending on long you would like to cruise. Might be better to use mechanical power to turn the prop, although you won't have battery back up as suggested above.
David