RF grounding methods for sailboats: A Summary

This is a distillation of several recent postings and other readily
available information on securing a good RF "ground" for a vertical
antenna on a plastic or wood sailboat. The basis for each method was
either reported model results or a presumed "organizational authority" on the subject (i.e., ARRL, Icom, and SGC).

No ranking or recommendation was intended.

If anyone spots any errors of fact or significant omissions, I'd welcome appropriate "recalibration". Thanks in advance.

1) Grounding plates

Will not work if submerged as much as four feet, but will work as
near-perfect if at the waterline, and may work if attached to hull even
when submerged four feet (awaiting clarification from Roy, W7EL). In
fresh water or low-conductivity water, a ground plate may not function
acceptably. Sometimes used in combination with #4 below. Recommended
only "as a last resort" by Icom.

2) Wire in water

A one-foot length of wire immersed near water surface is sufficient for
near-perfect results based on W7EL's NEC-4 model results. Assumed
performance is similar to grounding plate.

3) Radials

Even shortened (loaded) radials elevated over seawater work as near-perfect based on N6LF's NEC-4 modeling. Objections to radials are safety (high-voltage insulation notwithstanding), tripping hazard, undesirable RF coupling, and the necessity of either tuning the radial(s) or installing multiple 1/4 wavelength wires. Radials will be useful even over fresh water or when boat is on land. Single radials can provide significant near-vertical radiation which may be useful, but at the cost of reduced radiation from the vertical radiator. Considered a viable alternative by Icom but not recommended by ARRL.

4) Counterpoise (i.e., mast, forestay, shrouds, lifelines, engine, metal
tanks, 100 square feet of copper, keel, rudder, etc. bonded together)

One of the traditional approaches to marine SSB installations on plastic
and wood sailboats. The mast and rigging often provide the equivalent of
~200 lineal feet of counterpoise wire above deck with additional metal
structures connected on and below deck. Sometimes used in combination
with a grounding plate. If copper is placed inside hull below waterline,
useful capacitive coupling to the water may occur. Will work over fresh
water and on land. This is the method recommended in the ARRL Antenna
Book, where radials, as the only considered alternative, are discouraged
in their discussion for the reasons stated in #3. This type of
counterpoise is also the approach recommended by both Icom and SGC.

5) OCF dipole w/horizontal component along deck

Not commonly used, but obviates the need for multiple resonant radials.
Analyzed by W4RNL. Usually requires a current choke in the coax from
tuner to rig to reduce undesired RF coupling. Suffers from some of the
same objections listed for radials; will also provide some
near-vertical radiation. Will work over fresh water and on land.



Is that where it stands, folks?

73,

Chuck,
NT3G



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Relevant Pages

  • Re: RF grounding methods for sailboats: A Summary
    ... The focus on "water surface" is as ... I doubt there is much disagreement on that, even though water might be characterized in relative terms as a "terrible conductor". ... Even shortened radials elevated over seawater work as near-perfect based on N6LF's NEC-4 modeling. ... This fact combined with tidal flows, man made pollution from storm water drains and other factors makes "connecting" to sea water seem dubious. ...
    (rec.radio.amateur.antenna)
  • Re: Yacht Rf ground and radials
    ... 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. ... Not any more efficient than a foot long uninsulated wire extending downward from the surface. ...
    (rec.radio.amateur.antenna)
  • Re: RF grounding methods for sailboats: A Summary
    ... That it will not work if submerged as much as four feet? ... The focus on "water surface" is as ... Even shortened radials elevated over seawater work as near-perfect based on N6LF's NEC-4 modeling. ... Richard Clark, KB7QHC ...
    (rec.radio.amateur.antenna)
  • Re: Yacht Rf ground and radials
    ... 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. ... Since the salinity of salt water is not constant using one or 2 radials on yacht would be more efficient. ... Not any more efficient than a foot long uninsulated wire extending downward from the surface. ...
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