Roy Lewallen wrote:
I put this aside until I could do a little modeling. A lot of postings
have been made in the interim, but I don't see too much in the way of
answers. I'll try to answer some of your questions.

I think we all would be interested in how a small piece of metal buried
in sea water can provide an efficient ground versus one or 2 elevated
radials. I also dont see how its efficient concentrating all your
current in such a small area. Since the salinity of salt water is not
constant using one or 2 radials on yacht would be more efficient.

Will wrote:
I want to set up a hf antenna for my sailboat.

I have read various guides from Icom etc.

They suggest running copper foil to a Dynaplate and use sea water as
the ground. How can this work when the Dynaplate is below sea water?

I don't know anything about Dynaplates, but if it's on the hull, it's
very near the surface of the water. Any current it conducts will flow
along the top of the water displaced by the hull. If, on the other hand,
it's really under any depth of water at all, it'll be invisible to RF
and might as well not be there.

Is sea water equal to copper wire radials as a RF ground system?

Yes.

Does sea water make a good enough ground without radials?

How can salt water which would have some resistance even though
its conductivity is high compared to earth behave better than copper
wire when returning antenna currents to the feedpoint. The small amount
of current flowing in a 100 watt signal i would not want to waste
sending it into salt water. Salt makes good resistors, why would you
introduce a loss into the equation which radials seem to eliminate
even though we dont have ground loss over sea water? We also have the
issue of the skin depth of sea water to consider.

Yes. A foot-long wire "ground rod" below the antenna provides a nearly
lossless ground connection at HF.

This is not how most yachts connect their ground connections. They
connect to the sea cocks well below the top of the water anywhere for
3ft to 5 ft down. Some even use slim flat ground shoes again well below
the water line. Its impractical for a any sail vessel to maintain a
connection to sea water close to the surface because loading and the
yacht heeling when sailing.

How can a piece of copper metal about 1 ft square equal several
radials laying on the boats deck?

Radial wires are used for land based systems because of the poor
conductivity of soil. Radial wires reduce the resistance of the path
current takes going to and from the antenna base. Salt water is a good
conductor and doesn't need -- and won't benefit from -- radial wires.

Indeed radials do perform this way. I would still want to use radials
wires even 1 or radials wires even on a yacht since the length of the
radials will have a greater capacity to sea water ground. It also would
be more efficient in providing a current return.

Why do i have to use copper foil when most other people suggest using
ordinary copper wire?

You don't. And won't copper corrode rapidly in salt water?

Over seawater what would be the best number of radials to use
considering that maximum length i can run is 40 ft. I am planning to
use a backstay antenna with a SGC 230 Tuner.

None. A simple wire down into the water is adequate. Or use a small
plate very near the surface if you prefer.

Again yachts bury their ground connection well below the skin depth.
Some even run the ground wire from the tuner down to the keel which is
well submersed in salt water. All they are using is one short piece of
foil that is behaving like a small radial. We will see what the models say.

2 elevated radials over seawater versus a 1 ft square piece of metal
buried below the skin depth. My money would be on the radials.

Bob

Roy Lewallen, W7EL