Corrosion You Never Knew You Had

Tech Tips-The Corrosion You Never Knew You Had
By Bill Whitney
Face it. Your boat lives in a corrosive environment. goes up, the current available to the starter goes down even
Salt water, salt air, high humidity, dissimilar metals, hull sweat, further.
leaks, you name it; they all contribute one way or another to the In addition to having clean, corrosion-free connections
corrosion that inevitably finds its way onto your boat and mine. _on your batteries, it’s important to have the correct size lug
We all recognize it in its simplest forms like rust on steel, stain- _ connections on the ends of your battery cables. Lugs come in
less steel and iron parts or the white power, known as inter- many sizes. I can’t tell you how many times I’ve seen boats
granular exfoliation, on aluminum parts. Then we have the all —_ where the battery and electrical cables were grossly mismatched.
too common green verdigris on our bronze hardware and the The typical marine or commercial battery has a 5/16-inch post.
brown patina that paves the way for it. Because these forms of __ I have seen a boat owner use a 3/4-inch lug that was too big and
corrosion are readily recognized, and you can see it slowly floated loosely on the post. To get a better fit they sandwiched
eating up your precious boat, you usually attack it and try to the lug with washers. This is not good practice! Matching the
eliminate it and its source or at least control it, which is really all _ correct size and type of lug on the cable to the post will provide
you can do. a much more secure and electrically superior connection to the
Unfortunately, there are many hidden areas on a boat _ battery.
where what we don’t see we don’t address on a routine basis. To clean battery and other important connections, I use
When was the last time you looked at the back of your electrical a rag moistened with a little kerosene or diesel fuel to remove
panel? Another common spot that is routinely forgotten is the any preservative or grease, then a red Scotch-Brite pad, fine
big high current electrical connections on the batteries or, more —_ sandpaper or a small wire brush. (Be careful not to remove too
importantly, the ground connection on the engine. If you much of the soft copper or lead surfaces you are cleaning!)
service the batteries annually like you should, the idea of clean- After cleaning and reconnecting the battery terminals, I highly
ing the connections has at least crossed your mind. But you recommend coating them with one of the several anti-corrosion
may not have recognized what a little corrosion, or a poor products like CRC, Permatex or Gunk. These are available in
contact between the battery post and cable can create if you spray cans at auto parts stores or your local chandlery, and
didn’t clean the mating surfaces. provide good protection from battery acids and salt water, and
Consider for a minute the amount of DC current it help keep corrosion at bay.
takes to start your engine. Depending on how cold it is and the The same principles apply to the other electrical
size of your power plant, it could take up to 50 Amps or more _ connections on the boat, especially those that may occasionally
from the battery to the starter motor to roll the engine over. Any _draw a lot of current. Master battery switches, autopilots and
dirt or corrosion between the connections creates a resistance to _ master electrical panel switches are all candidates due to the
current flow. So if the connection at the battery, at the ground —_ environment in which they exist. It’s common practice in the
connection on the engine, or anywhere in between is corroded, __ electrical power industry to routinely inspect and possibly shut
less power is delivered to the starter motor. Think of this in down power panels to re-torque the nuts and bolts that hold the
terms of water flowing in a pipe. electric connections together. Admittedly, we aren’t producing
the high currents and voltages that commercial power plants are,
Where: Rate of water flow = Water pressure but considering the more challenging marine environment our
Size of The Pipe boats live in and the continuing movement and vibration found
on boats, it’s not a bad idea to do an annual corrosion inspection
Electrically this equates to: Current = Voltage on the battery and other high current connections. Additionally
Resistance I’d suggest that every five years or so a closer look at the other
The rate of electrical current flow is similar to the water “trical connections may be in order.
flow. The water pressure equates to the battery’s state of we yy Ue
charge, with 13.8 Volts being a fully charged battery and the mela y fe ZZ
size of the pipe restricting the total amount of water flow ee t Me
through the pipe equates to resistance. # fi f’ 4
If, for example, you have a very small amount of resis- J aire Ca eal j
tance (.5 Ohms) in the circuit, the maximum amount of current a gh tek Pe 7 ae Mi Ud
delivered to the starter with a fully charged (13.8 VDC) battery > jammies La.
would be: Sere
27.6 Amps = 13.8 Volts aN ers 4 a
ms Ohms ia eS a
So you can see that if you needed 50 Amps to get the
engine spinning over fast enough to start, that half an Ohm (.5)
of resistance isn’t helping. And worse still, as the resistance Tannis #7, over hard in a fresh breeze in 2018 in Rockland,
~6- Withno shortage of crew holding down the windward rail.
(Bill Finch photo)