Advanced Marine Electrics and Electronics Troubleshooting A Manual for Boatowners and Marine Technicians

potential. The idea is to make sure that

the potential reading you get with an

anode (or anodes) attached to the system

is at least –200 mV greater (more nega-

tive) than the average reading without an

anode attached. Actual numbers will vary

depending upon the number and surface

area of the anodes, as well as the specific

alloy the anodes are made of.

5 Compare your readings to the recom-

mended values in ABYC Standard E-2,

shown opposite, to see if your boat is ade-

quately protected.

The reading in the bottom photo opposite

is slightly more negative than the ABYC table

suggests. This is not unusual and represents

no problem in the case of a fiberglass boat. All

that is implied is that the anode surface area is

slightly greater than needed, and since the

boat being tested just recently had its anodes

replaced, this is to be expected. As the anodes

are depleted, the exposed surface area will be

reduced and the voltage potential will become

more positive. In fact, I generally recommend

adjusting the anode area to give a slightly

more negative reading than the ABYC table

suggests as a starting point, knowing that in a

relatively short period the numbers will fall

within the prescribed range. All this does in

effect is increase the effective service life of the

anodes by a few weeks or a month.

What if your readings do not fall within

the ranges recommended by the ABYC E-2

standard?

If the readings are less negative than rec-

ommended, your boat does not have adequate

anode surface area exposed to the electrolyte in

which it is floating. There are two explana-

tions for this scenario:

1 If the anodes have been doing their job for

the better part of a boating season, then

the situation is normal. The decrease in

surface area means the zinc material has

been sacrificing itself (eroding) to protect

110 electrical systems troubleshooting

12V 0V

Through-

hull

Radio

Ground

plate

Bonding

Zinc

Common

Battery ground

Silver-

silver chloride

electrode

Digital multimeter

on DC volts

Testing your boat’s corrosion potential. (Reprinted with permission from Boatowner’s Illustrated Electrical Handbook,

second edition, by Charlie Wing)