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?

--
Brian Reay
www.g8osn.org.uk
www.amateurradiotraining.org.uk
FP#898

Hello Brian,

Interesting question you've posed.

Theoretically, AC will not cause a problem. Practically,
however, it can be troublesome. Being AC, of course, RF may
similarly contribute to galvanic corrosion.

The good news is that the RF ground currents will be spread
over what may be hundreds of square feet of hull submerged
in water. The current density anywhere is likely to be quite
small. I suppose it could be roughly calculated if you are
curious.

But there's even more good news. Unless your friend plans to
run a broadcasting operation (kidding, of course), his
actual time on the air will typically be small in any 24
hour period.

So, small current density and a duty cycle of only a few
percent suggests that this will not be a problem. I have not
heard of any instances of galvanic corrosion resulting from
RF currents passing thru a metal hull, but there will
doubtless be others posting here with the ability to offer
counsel of greater substance and broader experience than this.

Good luck!

Chuck





Brian Reay wrote:
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?

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?

Larry W4CSC wrote:

(The FCC took a dim view of the operation and confiscated
everything a few weeks later,

You were his chief engineer and the feds found out you only have a ham
license?

Can't believe you have the balls to show your face here again.

Rick

If the AC or RF does not have any DC component it should not cause a
problem.

His radio (and antenna tuner) should be grounded to the hull via
capacitors,
This should create a low impedance path for the RF but block any DC.

If he powers his radio via a 12vdc power supply powered from the AC mains
the transformer would block the DC.

I assume ih will have a lightning arrestor at the antenna mount for statis
or lightning protection.
He should use a gas discharge type lightning arrestor that does not have a
DC path.

I'd to work him when he has his station set up.

Regard's

Mike N2MS

"Brian Reay" wrote in message
...
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?

--
Brian Reay
www.g8osn.org.uk
www.amateurradiotraining.org.uk
FP#898

Brian,

This West Marine Advisor articel has a good writeup on RF grounding...

http://www.westmarine.com/webapp/wcs...gsystems.ht m

Regard's

Mike N2MS