The submerged flotation gives seasteads a lot of drag. However, friction from drag is proportional to velocity squared, so as long as we move slowly its still manageable. Renewable energy could be used to directly power a propeller. For example, simple vertical-axis wind turbines could be connected directly to propellers, or the up-and-down motion of waves could be converted to rotation. Or we can use our standard methods of electricity generation to power electric trolling motors. These methods will appeal to the environmentally conscious, since they do not require burning fossil fuels, and may even prove to be cost-efficient. However, they are unlikely to generate much speed.