Bonding and Grounding Systems

Tech Tips #5
by “The Old Salt” (Bill Whitney)

Goodness! It’s already June! Where did the time go? Here So, what’s going on! The problem stems from the electrical
am, sitting in the workshop, surrounded by boat projects, system at the marina and the other vessels plugged into the
hoping I can get them all done before the end of the month. All system. The problem is transmitted to your boat and any other
the paint, varnish, terminal strips, wire, and other parapherna- _boat plugged into the system through the green ground wire of
lia that keeps the discount chandleries in business seem to reach __ the AC wiring system that you so conveniently connected to the
a peak in June before it gets to the boat. Hope I get it all done ocean in and around your boat via that common ground connec-
by the end of the month. One of the projects that I have tion – your engine.
managed to complete is to install a separate ground for the AC Under ideal conditions, as long as the marina wiring is
wiring system. It’s also time to look at all of the seacocks and _installed according to the National Electrical Code (NEC), and
see if there are any signs of galvanic corrosion. Strangely _no other boats are plugged in, you have little to worry about.
enough, those were two of the topics that were on the original Problems arise when the marina’s electrical system corrodes or
list of articles 1 was planning to write. In case you don’t connections loosen with age. As the AC current in the less than
remember, the topics are; electrical wiring, alternators and __ ideal wiring system increases, voltages can be induced in the
regulators, battcrics, grounding and bonding, radios and anten- ground wire that create a small current through the ground
nas, and instrumentation (depth, speed, GPS, LORAN, etc.). In connection to your engine. Another cause can be other boats
this article we’ll look at electrical system grounding and how it _that are plugged into the AC system. If they have an electrical
can impact your boat if you don’t pay a little attention to your —_ problem, and the same common ground connection, you have a
ground connections now and then. problem. Any stray ground currents created in the marina’s

Once again, I would like to solicit questions from readers. _ wiring or galvanic corrosion problems created on other boats
After all, this column is intended to be the place where you, the can be coupled to your boat through that green ground wire.
reader, can submit technical questions and either obtain If you have noticed that your engine zincs seem to waste away
answers or direction to appropriate reference material. over the course of one season, you may have a problem. The

The DC System components in a boat are usually the easiest best way to avoid the problem is to unplug the AC power cord
to understand. We have already presented its components: when you don’t need it. This way you have removed the
battery(ies), alternator, regulator, and wiring in previous connection that was being provided by the green ground wire.
articles. In general terms the battery produces the electrical Another way is to isolate the ground or install an isolation
energy that you need, the alternator replenishes the energy you _ transformer. I don’t recommend the latter solution for our size
consumed, and the regulator tells the alternator how much __boats however, since they are both expensive and heavy. I do
energy to replenish. The wiring delivers the energy to the recommend minimizing the use of the AC shore power cord,
system components. In a DC system the negative (-) side of the and keeping your DC system as clean and healthy as you can
battery is normally connected directly to the engine block. The One of the other symptoms of this AC ground current
primary reason for this is that the starter motor usually has the __ problem can also be accelerated deterioration of other underwa-
highest current draw of all the other electrical components in ter components of the boat. In wooden boats this can include
the system; and running the negative side of the wiring directly the screws, boat nails, and other fastenings that hold everything
to the engine block near the starter is good design practice, as it together. Unfortunately many of these may not be visible, so
keeps any voltage drop in the wiring to a minimum. you can’t inspect them. You can, and should, look at all the

At the same time it also creates a problem; especially if you other fittings. These include the zincs, seacocks, valves,
have both DC and AC electrical systems. General practice is to stemhead fittings, rudder fittings, straps and engine accessories
connect the green wire of the three-wire AC system to a that are exposed to saltwater. Any heat exchangers on the
grounded point on the boat. That point is normally a terminal engine should have their own sacrificial zincs. If you have
Strip that is also used for the black wires of the DC system; and never checked them or worse yet don’t know where they are
that’s connected back to the engine block. Well, under normal _ located, get out the engine manual (or see your mechanic) and
conditions, when you are out sailing or hanging on the find them. Nothing will ruin a cruise faster than having all
mooring, the common connection of both DC and AC grounds —_your oil pumped out through hole in the engine oil cooler.
does not have any adverse effects. But if you have a slip ina Admittedly these are sail powered vessels, but my blood
marina, and plug in the AC system for any sustained length of pressure doesn’t need the boost it gets tacking through a
time, you could be creating a condition that not only eats up crowded mooring field trying to get to my mooring. The
your engine cooling system zincs (you do know where they are _ challenge is a lot more fun knowing that you have a reliable
located, don’t you?) but also sets up a condition that can devas- engine to extract you from disaster should anything go wrong.
tate underwater boat fittings. (Continued to Page 7)

Inspect the valves (and other bronze components) by taking
them apart and looking at the interior and exterior surfaces. If
you see a pinkish tinge on the bronze surfaces it indicates that
the zinc is being leached out of the bronze. You need to inves-
tigate! Either you have an AC problem or you need to add more
sacrificial zincs to protect the components from galvanic corro-
sion. Selecting the right amount of zinc to a hull and selecting
the appropriate location for it is not that easy. If you know
what was used on your boat in the past, and know where it was
located on the hull, restore it to that original location and use
the same size that was used originally. You can cause yourself
problems if you use too much zinc.

Master Mariner Co. used to manufacture a corrosion meter
that was very useful in determining the level of protection being
provided to underwater metallic fittings. Basically it is a very
sensitive meter, called a galvanometer, that is hooked between a
reference cell that is placed in the water beside the boat and the
metal fitting being tested. If the meter indicated a balanced
reading in mid-scale it indicated that the fitting was not being
subjected to galvanic currents that would either eat it away or
deposit metal from another fitting on it. In effect it was in a
neutral, protected, environment. If you can locate one of these
meters or its modern replacement I think it is worthwhile to
spend some time measuring cach fitting, and cither adding (or
reducing) your zincs to get the protection your fittings need.

There are folks around that specialize in marine corrosion
problems, but I don’t know any of them personally. Your yard
or surveyor should be able to recommend someone if you don’t
want to tackle the job yourself. Good luck.