Importance of maintaining “dynaplate” style ground plates

Question, Is this really a Dyna-Plate or a big zinc plate you are asking about?

The Dyna Plate makes for a great electrical contact with the water. Not a smooth surface but like open cell foam. Usually made of better bronze.
This grounding makes for a great Di-Pole effect for SSB transceivers. Also dissipates other electrical noises.
On out Bert, We have 2 original plates that seem to be still like new condition 44 years later.

When living around marinas, our zincs could last yearly to just a couple of months.
When a new neighbor backed into the next slip, You could near exactly determine when your zincs would need to be replaced.

So, if your zinc plate was to be replaced, maybe it was and already burned off.

New boat to you?
If you have a bunch of wires going to it and it burned away like a zinc, you may have a problem device leaking current to it.
I don't think I have ever heard of a Dyna-Plate burning away, even after a lightning strike.
Do you have SSB on board?

Well, that is an old Dyna-Plate, and the other is a zinc.
Never witnessed a Dyna-Plate installed so far back or in such bad shape.

I would say at one time (or two), some bottom paint with copper/tin was over it.
If your not using a SSB, I'd remove them, fill the holes properly and move all the remaining wires to the transom zinc plate.
You may want to inventory where all those wires came from/go to. I still do feel something is not correct.

Now that I slept on it; I would find out what is at fault first and fix that first.
Dyan-Plates just don't wear away..
Dyna-Plates are not sacrificial like a zinc.

If that's your ships picture to the left; they are probably used for a lightning path.
So, scratch my idea of removing them, you may consider improving them.

They should already be tied together.

Dyna-Plates are not for passing fault current (except for lightning).
They form the reflective end of a Die-Pole antenna and dissipate other electrical noises.

Not a ground, Battery negative should not be present on them.
Not a primary part of the bonding system but may be tied to it.
Not connected to the gen-set(s).

Consider this;
You just spent LOTS of money on your ships purchase.
Please don't be-little your ship by not investigating all faults and improve the safety of your investments.
Please consult a REAL marine electrician, show him my notes here.

Captain Ralph Crapps
Marine Solutions & Associates, Inc..

Please do..

Looks like you have a ground fault on one of the ground wires connected to this particular dyna plate. Easy enough to trouble shoot the ground fault by isolating the individual grounds off of this plate while using a VOM on millivolts positive vom lead on the individual ground wire off of the plate and neg vom lead on a solid ground like and engine block or through hull and this will identify the circuit causing the fault. You then have to start isolating individual equipment off of this circuit until found. The dyna plates porous bronze material was made that way to increase overall surface area for counterpoise or ground plane for HF radio installations. These were generally tied to glassed in flat metallic screens under the helm/ Fly bridge on some manufacturers and normally had 3"copper strap or copper tape in lieu of a round copper conductor due to more surface area of the flat strap. Copper strapping would run from the auto tuner or coupler down to the plate. While this ground plane will make it easier to tune the auto coupler matching the antenna it has zero effect on what type of antenna that's being tuned be it a loaded coil, trap, long wire or dipole, makes zero difference.

You're looking for a + millivolt reading. Could be slight .004 up to a few millivolts. Depends on the severity of the ground fault. Could be a bleed from Florescent ballasts, small transformers, electric motors etc. these are usual suspects for ground faults on the alternating current side of things. Same holds for the direct current side. Plenty of "how to" concerning tracing ground faults online for you to reference.

Many times it's a simple as a wet or flooded junction box.