The idea is not perpetual motion as long as you're not trying to extract energy for propulsion directly from a head wind. You could, however, certainly use a wi

The idea is not perpetual motion as long as you're not trying to extract energy for propulsion directly from a head wind. You could, however, certainly use a wind turbine to store energy while not underway (e.g. while in port trabsferring cargo or at anchor) and then use that energy to propel against a headwind later. (I'm a marine engineer and work on ship propulsion system design, specifically WRT energy efficiency of propulsion systems.) The challenge with a hybrid wind turbine-electric propulsion would be the energy efficiency losses from turbine generator through a power conversion (and probably storage) device and ultimately the propulsion motor. By the time you're finished, it probably would have been more practical to use some type of sail to harvest wind energy for propulsion directly with no losses. For a head wind, your wind turbine would be harvesting energy, but it would also be creating significant air drag which would be added to the total resistance of the vessel, so the sum total of propulsive power would be negative in a direct head wind scenario. Interstingly, the opposite is true for a tail wind - that is you'll be gaining thrust (like a sail) in addition to harvesting some of that energy. Again, though, because of the energy conversion losses, I think you'd probably get better propulsive efficiency if you just used a sail, which has no energy transmission losses. I think the best case for wind turbines on ships is to use them for energy harvesting in port and in tail winds. I'm sure someone is doing this, but you need to balance the initial hardware investment and operational maintenance costs against the potential fuel savings in order to justify the installation. There are a large quantity of energy harvesting/conserving technologies out there that are trying to take profit the IMO restrictions (which is a very good thing I think). The interesting thing is that global shipping is only a few percent (used to be 2%) of the worlds transportation carbon emissions, but it transports the most tonnage of any mode of transport. My point is that, while all of this focus on the shipping industry is necessary and very interesting to me personally, things like converting automobiles or airliner emission is much more of an environmental impact.