I believe sails are more efficient than an equivalent sized windmill, if you
are considering "lift to drag" ratios. This is irrelevant when the windmill
is bolted to the ground, but important for a boat (unless it's at anchor).
For instance, if you are generating electricity on a long cruise it's more
efficient to have the sails push the boat and generate electricity from
dragging a prop in the water than generate the same electricity from a
windmill.

There are additional engineering problems, such as centre of gravity,
gyroscopic effects and "reefing" issues.

Years ago I saw a Popular Science picture of a windmill cat with a long
inclined shaft that ended in a prop in the water. It's best (and likely
only) point of sail was straight into the wind.

I have seen large vertical axis "egg beater" windmills in New Zealand. These
would have many advantages over horizontal axis Propeller windmills for this
application, but I've never seen them used on a boat, even for generators.

I may be wrong, but I don't believe Cousteau's Turbosail captures and
mechanical energy for the prop. I think it generates a net cyclonic flow
around the mast/sail to increase "lift", the way the backspin on a golf ball
creates lift. Apparently the broad, flat light "monocat" hull has such a
high roll frequency that it incapacitates the crew with seasickness in
snotty weather.

I think there is a reason boats look like boats... at least boats that work
like boats are supposed to...



Bruce




"slvrspun" wrote in message
...
Just an off-the-wall question, and couldn't think of anywhere else to
send it to

I was thinking a while ago that one or several windmills could harness
the energy of the wind as much as sails, and also be made to continue
providing power to a drive shaft and propellor even when the wind is
blowing in any direction, by turning the face of the windmill(s) into
the wind.

Possibly more expensive, but much simpler to operate, because a
ships's pilot would just allow the windmill's sails to turn, and then
decide how much torque to accept, and then steer it with the rudder as
per normal.

Is this a feasible idea?


slvrspun :-)
--
A place for everything, and everything in it's place.
Samuel Smiles - Thrift, Ch 5, 1875