Bondingelectrically ties together all major
fixed metal items and then connects them to
the boat’s ground. This has two purposes:
1 It removes the conditions for current to
flow. The key to inducing electrical cur-
rent flow in metals is a difference in volt-
age potential. If there is no potential dif-
ference, there can be no current flow. By
electrically tying all of the underwater
metals together, we create an electrical cir-
cuit where no potential difference exists,
therefore no current will flow. No current
flow, no corrosion.
2 It removes the possibility of an inappro-
priate path to ground, such as through the
hull or through-hull fittings. Bonding
maintains a low-resistance path back to
the battery.
In the United States, the bonding approach
is commonplace. Underwater metals con-
nected via a bonding system will polarize (see
below), and as long as they are connected to
an appropriately sized anode—either zinc, alu-
minum, or magnesium (depending on the
location of the vessel)—the anode will become
the sacrificial lamb in terms of corrosion. One
argument against this approach concerns out-
side forces, such as current leaks in the water
at a dock that can migrate and be distributed
via a bonding system inside the boat. So some
builders believe isolating the metals is a better
a basic corrosion survey 107
*the single point at which
all the bonding and grounding
circuits are tied together
DC
equipment
accessory
negative bus
overcurrent
protection
branch circuits
distribution panelor switchboard/panelboard
windlass
DC
negative bus
float
switch
bilge
pump
parallel switch
or solenoid
main
feed
battery
switch
house
battery
battery
switch
engine generator
(AC or DC)
battery
switch
battery negativeengine
terminal
DC main
negative bus*
battery
fuel AC grounding bus
tank grounding
bus bonding cable
chainplates
seacock
strainer
metal objects
main lightning
down conductor
electronics
ground plate zinc
immersed ground
plate or strip
current-carrying
normally non-current-carrying
chainplates
A bonding system. (Reprinted with permission from Boatowner’s Mechanical and Electrical Manual,third edition,
by Nigel Calder)