To Ground or not to Ground. That is the question?

[Pete7]

Originally Posted by deblen

Just a personal observation.
Most EU boats go to great lengths to bond every underwater metal to each other with substantial "inside" bonding wire plus many use a "ground" plate.

Many N.American boats have none or little of this bonding.

Are you sure, or is it the other way around?

My EU yacht has the AC earth and DC negative bonded together at the switch board by the manufacturer Moody and from there the DC negative is bonded to the hull anode. None of the seacocks are bonded, nor the twin keels. The propshaft has its own anode. The rudder shaft and P bracket are bonded to the hull anode as is the 12v DC negative.

This is fairly standard for an EU yacht, unless someone has been buggering about with it.

Whilst I acknowledge Jedi's advice is top notch, cost and space for a huge blue box on a 31ft yacht are problems and why we may only fit a galvanic isolated at best. Particularly since we use so little shore power.

Pete

[s/v Jedi]

Originally Posted by deblen

Just a personal observation.
Most EU boats go to great lengths to bond every underwater metal to each other with substantial "inside" bonding wire plus many use a "ground" plate.

Many N.American boats have none or little of this bonding.

Both EU & NA boats generally use shaft/prop/strut zincs.

In many years of reading "corrosion" posts,I detect no difference in performance of either system on fiberglas boats.

If a serious zinc/metal eating problem arises,it is usually found to be leakage of "hot" to the surrounding water,as opposed to DC bat negative or AC green wire earth to the water.

Earthing and/or connecting DC neg to the mast :
I have seen the results of a floating mast becoming DC hot,due to a lighting wire,or other 12V + source shorting to the mast.If the mast is DC neg connected,a fuse/breaker will blow. If it is floating,or only earthed to the water,current will flow thru any path it can find,back to DC neg. This will usually be the VHF ant. braid & radio and/or the water to the prop & shaft which are attd to DC neg at the engine.

I suggest any lightening earthing of the mast,etc., be thru a lightening spark gap,to prevent DC flow. I also suggest that the mast be connected to DC neg with #10 (or so).

I have personally seen no evidence of the need or benefit of bonding each or any proper thru hull fittings on a fiberglas boat.

Above are my personal observations & opinions only.
Cheers/Len

I believe bonding is a requirement of the ABS certification. I have seen many bonding wires on American boats and they all love connecting electrical systems to the water. But this is off topic and doesn’t really matter much.

So let’s look at this in more detail:

1. Underwater metals. Galvanic corrosion happens when you insert two different metals into the water and make an electrical connection between them. This causes the less noble metal to dissolve.

First observation: do not make electrical connections to these metals and you don’t need protection systems to begin with.

There are exceptions: underwater structures that are assembled from different metals and also certain alloys that have internal corrosion at the molecular level. An example is the prop shaft and propeller. These parts are electrically connected to each other and different metals are involved. Even bolts/fasteners count. So this must be protected and we do this by adding zincs.
For alloys that corrode: simply do not use them and if you already got them, replace them. Many production boats have brass fittings used underwater. Replace those at the first signs of corrosion with bronze or plastic, making sure you don’t just buy from the chandlers shelve but research the good brands and even models within a brand before spending money.

2. So we have an engine. The starter motor uses the metal block as DC negative. So does the alternator. So does every sensor that needs a DC negative return path. Stupid! but cheap, saves money
You can try to isolate things but that’s all costly and difficult. I like to see things like engines be kept as they come from the OEM so recommend to keep them as they are, but that doesn’t mean hook them up to AC power and other weird things people do with them. I actually recommend to remove all electrical connections when they aren’t needed. So I remove AC ground permanently after installation of an isolation transformer for shore power (or remove shore power completely for solar powered boats) and creating a separate AC ground aboard and converting to double pole breakers.
This leaves DC power. Install disconnect switches in both DC positive and negative conductors (I believe there’s double pole switches too) and keep those in disconnect position whenever the engine isn’t needed.

3. Why builders connect bonding wires between underwater metals: often this is done to make a zinc protect other metals that don’t have a zinc. Other times they do it without having a clue as to why.
So if an underwater structure has different metals, add the right amount of zinc anodes (measuring this using a silver chloride reference cell) and when you have inferior alloys then replace them with the good stuff. Remember that stainless isn’t good underwater either. I have a Monel prop shaft. Stainless steel needs air contact so limit use underwater as much as possible.

4. Safety codes. These are needed to keep people and boats safe but often a pain. This is because they are under pressure from manufacturers and the market demanding cheap solutions. Also, most people are clueless, example: they connect secondary side ground of an isolation transformer to the water because when they don’t, the GFCI outlets don’t function. They actually create dangerous alternate return paths so that they can install gear that protects people from those dangerous return paths even though they invested into eliminating those dangerous return paths completely

[K1MGY]

Originally Posted by deblen

I suggest any lightening earthing of the mast,etc., be thru a lightening spark gap,to prevent DC flow. I also suggest that the mast be connected to DC neg with #10 (or so).

Cheers/Len

Len, I am considering the install of an isolation/spark gap protector for my (two) antennas (one VHF/AIS at top of mast and a big dual band vertical on one of the upper spreaders for Amateur Radio).

Would you suggest the isolator be installed at the antenna coax connector or can it be done before the radio gear, in the cabin?

Also, if the mast is DC grounded, then it is also AC grounded (inside the boat after the galvanic protection diodes), and so then are the keel bolts. Yet, I read that keeping the mast and keel bolts bonded but not connected to the common DC/AC ground is best.

Again, I am confused

[deblen]

[Bowdrie]

In an earlier post I had said that connecting the mast step to the keel would be a reasonable "first step", and also said that their were other methods that improved on that.
A previous post mentioned the idea of a "gap" in that connection.
That is how my set-up is, as the distance between a keel bolt and the mast step is only a few inches, a simple piece of bent bronze and a bolt are rigged to give about an 1/8th in, gap to the step.
This keeps the mast isolated, but if lightning strikes the gap will ionize and conduct to the keel.
In many boats the headstay fitting is also part of the anchoring system as well as the pulpit, (perhaps also a bowsprit/bobstay).
If that be the case, (and the mast is directly connected to the keel,) then you have a scenario in which the whole assemblage of mast, rigging, both pulpits, lifelines, chainplates, and anchor rollers are all connected up electrically, (especially if the AC ground is connected to the DC negative per ABYC).
I personally don't want that, others may disagree, and indeed I've read posts on other forums in which reasons have been given for connecting everything up together.
Neither do I want a set-up where a lightning strike travels thru the engine, (fusing the bearings and ruining both engine and transmission,) on its mad dash to the sea thru the prop shaft.

[shimari]

Originally Posted by s/v Jedi

...

3. Why builders connect bonding wires between underwater metals: often this is done to make a zinc protect other metals that don’t have a zinc. Other times they do it without having a clue as to why.
So if an underwater structure has different metals, add the right amount of zinc anodes (measuring this using a silver chloride reference cell) and when you have inferior alloys then replace them with the good stuff. Remember that stainless isn’t good underwater either. I have a Monel prop shaft. Stainless steel needs air contact so limit use underwater as much as possible.

....

Our Southerly (built by Discovery) has all of the thru-hulls bonded to a large zinc attached to the hull.