Before connecting the radio into the boat, measure from the DC power leads
to the shield of the antenna connector. Many radios have the DC negative
lead directly connected to the radio's chassis and antenna coax shield.
This would connect his negative DC power (batteries) directly to the hull
where the antenna tuner is grounded to the hull. If his DC system was
isolated from the hull, of course, it would no longer be after such a radio
was installed. Galvanic action may be the results if stray DC currents
flowed through the radio.

As far as the RF current eating the hull, he is correct. RF current will
consume the hull of a steel ship, just as bad as any other ionizing DC or
AC current would. A religious nut, RG Stair, who runs a religious commune
in Walterboro, SC, for his own enrichment and grandisement, bought an old
Canadian Fishing vessel and a 40KW TMC HF transmitter circa 1960, the
latter from the stupid Federal government's own Voice of America. The
transmitter was installed in the fish hold with another powerful AM
transmitter. The antenna system was two T-topped cage antennas strung
between four big self-supporting towers welded to the boat's steel decks.
Power was from two 100KW diesel gensets also welded on deck. This powerful
HF transmitter was eating holes in the hull underwater, even with a ring of
grounding blocks, in no time at all after they fired it up just above 7.3
Mhz in the Wando River they were anchored out in. (The FCC took a dim view
of the operation and confiscated everything a few weeks later, negating the
hull eating problems.

Of course, your little HF transmitter isn't on the air 24/7/365 and isn't
running a few hundred RF amps through the hull, either. In the very
intermittent SSB use the boat will be using the transmitter, at 150 watts,
such a very low RF level and hull currents, it shouldn't take over 500
years to cause the hull to be eaten away. I'd be much more afraid of that
DC connection through the radio's ground system.



"Brian Reay" wrote in
:

I've got a query re galvanic corrosion and radio transmitters.

A friend of mine lives on a steel Dutch barge moored in a sal****er
marina. He has a transformer isolated mains supply and a number of
'sacrificial anodes' around the boat. On the boat side, the hull is
isolated from his mains wiring 'boat side'.

He plans to erect an antenna for HF use (amateur radio rather than
marine use) which, depending on the antenna type, may require an earth
connection. From the RF point of view, using the hull (and thus the
salt water) would give him a good RF earth but he is concerned re
galvanic corrosion problems.

I'm not an expert on galvanic corrosion but my logic tells me there
shouldn't be a problem- any currents would be AC and (I believe) only
a DC differential can accelerate galvanic corrosion.

Ideas, views, comments anyone?