This could be a little misleading.

Horizontal antennas perform just about the same over salt water as they
do over regular ground, with one exception: If the horizontal antenna is
low, very high angle waves will be attenuated when over real ground, but
won't be attenuated nearly as much if over sea water. The radiation at
zero elevation angle is zero for any antenna height and ground
conductivity. So there's nothing about sea water that would make a
horizontal antenna work worse than over ground.

However, a vertically polarized antenna has much stronger low angle
radiation when over sea water (*) than when over plain ground. And this
low angle radiation can be much stronger than anything but a very high
horizontal antenna. So a vertically polarized antenna is usually the
best choice for a boat.

I also don't think that an L antenna is the best idea, especially if the
horizontal part is low. If it is, the horizontal portion radiates mostly
straight up, wasting part of your power. It's a better idea to make a T
shaped antenna. Then the top will radiate very little, leaving most of
the radiation to the vertical section.

(*) The important factor for good low angle radiation is the ground
conductivity at the point where reflection occurs, rather than the
conductivity just under the antenna. For lower and lower angles, the
reflection occurs at farther and farther distances from the antenna.
Also, the reflection occurs farther away as the antenna gets higher. For
typical HF antennas and low angle propagation, the important region is
on the order of up to a few hundred feet from the antenna. Efficiency is
a separate issue, and for that, the important thing is the conductivity
just under and close to the antenna. Having the antenna directly over
salt water makes getting a good low loss ground connection easy, as
another poster pointed out.

Roy Lewallen, W7EL

Richard Harrison wrote:

Gary, K4FMX wrote:
"Are you saying that my low (less than 1/2 wavelength high) horizontal
antenna will be next to useless if I live on the sea shore?"

No. Your antenna will do whatever it does. I said that sea water
reflects so well that the reflected ray from the sea is almost as strong
as the incident ray. At low angles they cancel when horizontally
polarized, being equal and of opposite polarity, and this eliminates
low-angle radiation. This is demonstrated in Figs. 13 & 14 on page 3-12
of the 19th edition of the "ARRL Antenna Book".

Low horizontal wires tend to send most energy straight up. This can
provide near vertical incidence contacts.

For distance, when the reflecting surface is good (sea water) and the
antenna is low, the antenna had better be placed vertically. Results are
shown in Fig 16 on page 3-13 of the same book.

Best regards, Richard Harrison, KB5WZI