Just about every antenna imaginable has been tried on boats and ships. While in Morocco many years ago, I used to talk regularly with the radio op on a ship who had brought his own 5-element monoband yagis aboard for 15m and 20m. After the captain made him take them down, they ended up atop my house in Rabat...but that's a long story :-)
At dockside or in an anchorage it is possible, of course, to mount just about anything. I've even talked to sailboats which had yagi's atop the mainmast. But, clearly they weren't sailing with those in place!
To me, a practical
marine antenna has to be one which will be suitable for real ocean sailing, not just one you can rig while dockside. Thus it has to be very strong and built of materials which will withstand the rigors of the marine environment, including storm-force winds and high seas. That's why I favor marinized vertical dipoles -- in addition to the traditional backstay, of course -- and have posted details of their construction here:
Gallery :: Constructing a Marine Dipole Antenna
(click twice on each pic for full resolution)
and details on how to tune a marine dipole here:
SSCA Discussion Board :: View topic - How to Tune a Marine Dipole Antenna
The major limitation of these dipoles is that they are single-band only. That's fine if you mainly use one band, e.g., 20 meters, for long-distance communication.
I've explored the many ways of building multi-band vertical dipoles, but none of them meet my criteria of being truly seagoing. At dockside, of course, you could build such an antenna and it might outperform the backstay on several bands.