SSB grounding on a steel hull

[goboatingnow]

In Europe ISO boat standards have no requirement to "ground" anything in most cases

DC ground is a misnomer, its a current return path to the battery. It may or may not be at earth potential, on a schematic GND and Earth are different symbols. There is no need and in a metal boat an advantage not to to have a earthed DC ground.( or any ground to the hull).

There is a clear advantage in not connecting DC return to earth to AC protective earth wire on a boat. Again ISO does not require it as protection is left to an RCD. so called equipotential bonding is a "practice" that is not actually well though tout for metal boats in particular.

Bonded underwater fitments can cause more trouble then bonded ones and I personally see no point to them in a GRP boat for example. You are actually creating galvanic cell and a route to potential impressed current corrosion

ICOM specifically state that RF ground and DC ground () i.e. DC return) should NOT be connected, any one with electronics 101 can tell you why.

Also I would state that AC earth should not be connected to DC negative , let the RCD do its job, this prevents load dumping into the DC system. ABYC has a shortsighted view of this of course and doesn't allow it because its thinking follows NEC and its shortsighted views on whole house/whole boat RCDs.

RF ground is in effect part of the antenna system and the seawater makes any excellent counterpoise , If the hull is inert, then making it an RF ground ( install those DC blocking capacitors) is a very good idea. If the hull is part of the DC system ground, consider and isolated route to seawater, or if not possible separate RF ground point and DC ground point to minimise load dumping and raising the DC noise floor. By preference I would have an isolated path to seawater, if my hull is in the DC return path

Lightening protection is more then adequate on a metal vessel and needs not to be further covered here , its a distraction


Common mode voltage as a result of lightening are a complicated discussion and beyond most people here. ( and they arnt interested) its a complex subject with a degree of uncertainty of outcome. But its not a problem in the vast majority of people in day to day sailing.


be very careful of people that quote "code" and practice to you. Understand that around the world there are all sorts of national "codes" often that directly conflict with each other , ask yourself how that can be and maybe your "code" is wrong ( or not) YMMV. Look at thing from first principles and remember a boat is not a house.

Dave

[nofacey]

As OP, for the record:
- I have an isolation transformer to separate our AC system from the weird and wonderful world of dockside AC wiring
- we have not (and never will) use our hull as the 'DC return'. All circuits are double cabled.
- electrolysis driven by the differential created by grounding helter skelter is real, hence we have a common grounding point for all electrical systems.

I truly appreciate the RF grounding info shared, and will be grounding the antenna tuner to the hull via DC blocking capacitors.

[goboatingnow]

Originally Posted by nofacey

As OP, for the record:

- I have an isolation transformer to separate our AC system from the weird and wonderful world of dockside AC wiring

- we have not (and never will) use our hull as the 'DC return'. All circuits are double cabled.

I don't think anyone mentioned using the hull for that

Dave

[continuouswave]

Radios powered from 12-Volt batteries using antennas with a direct DC ground have been installed in automobiles for decades. The antenna is bonded directly to the car body, and so is the battery negative. The usual caution is to insert a fuse in both the positive and negative power leads.

As for the antenna tuner ground lead, it should be as short as possible and to the metal hull. If you do insert a DC blocking capacitor, it will need to have enough capacitance to be a low impedance at your lowest frequency. And you will have to weather protect it. And the voltage and current rating of the capacitor will have to be appropriate for the power. A Centralab 858S type capacitor of 1,000-pF should be a good start, if you can find one, or this Russian made version

1000-4 Doorknob Capacitor, 1000pf 4kv, Radio Komponent

If you are really worried about stray DC current on the antenna ground, then put a double-pole power switch on the power leads to the radio and antenna tuner, so when they are off both the positive and negative power are disconnected. That should eliminate any worries about stray currents or corrosion. You probably won't have the radio power up all that long.

By the way, I never liked vertical monopoles worked against ground, anyways. Better to put up a dipole or inverted vee.

My basis for this comment: radio amateur for 50 years; FCC First-Class commercial license for 40-years; built a lot of antennas.

73 de K8SS