Hi, Rich. All what you say is true. Now extend it to a fibreglass rowing
boat! The connection of the hull with sea water is of no significance at
all, as I'm sure you know. The pernicious idea that you can dump
unwanted electricity into the planet, dry(ish) or wet, is responsible
for more EMC failures than you can shake a mainmast at!
This confusion stems from radio transmission at low radio-frequencies.
At VHF and above, the transmitter's output is connected to the two arms
of a dipole (or other mechanical device that has effectively the same
electrical function). At lower frequencies, such a structure would be
too big, so one arm is simulated by an array of wires buried in the
earth. This acts as a mirror, so eliminating the problem of sinking a
300 foot mast into bedrock. There must be a continuous circuit,
otherwise no current could flow from the transmitter. The fact that we
can't see the energy flowing out as an electromagnetic wave is just due
to our limited visual bandwidth (just one octave out of at least 21
octaves in the electromagnetic spectrum).
The same thing applies at the receiver; for VHF and above we hoist a
dipole (maybe with extra elements to make a Yagi), which has two
conductors leading from it, but at lower frequencies we have to put up a
long wire antenna, connected to one side of the receiver input circuit
and connect the other end of the receiver input circuit to a buried
metal rod, thus setting up the continuous circuit. This has nothing to
do with some concept of a 'ground', with mysterious powers to absorb
however much unwanted electrical energy we throw at it.
Ground is whatever you decide has zero volts on it, so all other
voltages are measured with respect to it. In a digital wristwatch, it's
about a square millimetre of PCB foil.
Best wishes
John Woodgate OOO-Own Opinions Only
J M Woodgate and Associates www.woodjohn.uk
Rayleigh, Essex UK
On 2019-07-08 20:48, Richard Nute wrote:
Hi Peter:
Sea water is a very good conductor, better than soil. Fresh water is
an okay conductor. Pure water is a poor conductor.
The hull of a steel ship is well grounded in the ocean, and reasonably
well grounded in fresh water due to the large contact area with the
water.
If the hull is not steel, there usually are enough fittings that the
ship is reasonably well-connected to the water. The propeller and
drive shaft also provide a connection to the water.
I've heard of ship-board hams who will tow a large brass plate for a
good ground for their transmitter.
Commercial AM transmitters try to locate their antennas near a body of
salt water like San Francisco Bay or the Great Salt Lake.
I would guess that a ground pin of a shipboard outlet would be
connected to the hull metal. This gives the same protection from
electric shock as land-based outlets.
See also:
http://electrotechnical-officer.com/primary-methods-of-grounding-and-bonding-on-ship/
Best regards,
Rich
On 7/8/2019 11:19 AM, [email protected] wrote:
Hello group,
Is there a real ground in a ship? i.e if a Class I product is used
on the board of a ship, does the ground pin actually doing anything?
The ship is floating in the ocean and I cannot understand if there is
a real ground there or not? Can you guys educate me please?
Thank you
Peter
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