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

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)