I wish to hoist an antenna up a sailboat mast on a halyard to help
receive TV stations when out in the Chesapeake Bay. The challenge is
that the boat will rotate at anchor with the wind and even turn the
antanna on it's axis as it it "hoisted" by rope and not locked
rotationally.

There are commercially available antennas .. but it looks to me that
it's simply a "fat" folded dipole. I would think that I could
construct it's equivalent using the basic homemade folded dipole
approach.

http://www.boatenna.com/framesample1_000002.htm

Any other suggestions for a do-it-yourself antenna? It's not often
that I want to watch TV when on the boat (i.e. the reason I'm out
there) so I was hoping to build something myself out of thick guage
wire and 300ohm antenna wire.

Would 2 stacked folded dipoles with a 90deg offset (and "X") be an
effective approach?

If I just do the loop, what would you recommend the diameter be for
mid-range VHF5-13 or so?

Thanks in advance
Angelo