Of course, antennas on a ship are different from those on a sailboat, because you have a lot more room to play with AND you have a wonderful RF ground in the form of a steel hull and decks!
It is true, of course, that all the standing rigging on a sailboat will affect both the azimuthal and the elevation radiation pattern, so that a perfect omnidirectional pattern at HF frequencies is highly unlikely (though the VHF antenna atop the mast is pretty much omnidirectional).
Whip antennas on sailboats work well, and some experienced hams prefer them. You have to have a good RF ground system to work them against, of course, and if you're going to go to sea you need to be mindful of the whipping action of a long antenna. Mostly, these are attached on the transom, with some support at the level of the pushpit. Still, they can be a real bear in a seaway :-)
I actually carry three types of HF antennas aboard...have done so for years.
The first type is the "alternative backstay", similar to the traditional insulated backstay, but rigged separately with a good autocoupler at it's base. This antenna is very versatile and can tune any marine, ham, or other HF frequency. As I've said before, it's a good antenna, but not a great antenna!
The second type is the monoband vertical dipole: I carry several for different bands, and can rig up to two simultaneously on the foredeck. These dipoles give me a great advantage over the backstay antenna on long DX paths but, of course, they're only for the high bands (8 mHz and above) since I only have a 64' mast!
The third type is a mobile whip...the popular Hustler center-loaded mobile antenna, with changeable resonators for different bands. This is rigged on the pushpit and is really there as a backup, e.g., in the event of a dismasting. A full-size vertical would do better, of course, but the Hustler does a credible job when called upon. I had a friend on a Valiant 40 who used the Hustler as his only HF antenna, and we remained in contact during his voyages in the Caribbean, Bermuda, and the entire East Coast of the U.S.
Last edited by btrayfors; 03-19-2008 at 12:27 PM.