Well CC, what you are missing is an understanding of electrolysis.
Electrolysis is caused by dis-similar metals in contact with each other,
and
in the presence of a catalyst. (salt) It makes a sort of crude battery,
producing tiny amounts of electricity.

The electricity is made from stripping electrons from the "weakest" of
the
two metals. In this case, the aluminum of your hull. acting as an anode
to
the strongest metal (useually stainelss steel) acting as a cathode. This
has
the apparent effect of burning holes in the metal at the points of
highest
activity. Bronze items are electricaly neutral.

Electrolysis, otherwise known as galvanic corrosion, is especially bad
for
aluminum hulls, and will "burn" holes through the metal. Once burned
through, the hull is near useless, and, in general, cannot be safely
repaired. There are a couple of things you can do to minimize the effect
of
G.C.

1. Paint the hull with a good grade of zinc based primer, covered with
a
top coat of quality marine grade metal paint. This will isolate the
sal****er (catalyst) from the aluminum, and retard corrosion.

2. Install zinc (or magnesium for freshwater) anodes on both the motor
and
the hull. The anodes are sacrificial, and will decay in the presence of
galvanic current. They must be replaced annually or whenever they become
"crusty". DO NOT wait until the zincs are partially dissolved, as they
lose
their protective ability rapidly after the white "crust" forms. If you
are
the thrifty sort, save your old zincs for re-melting.

3. Bond the motor, hull and battery (-) side. Run a bonding strap or
wire
from the negative terminal of the battery to: motor block; motor mount,
hull, control panel, and any dissimilar metal on the hull. I.E.
stainless
steel Cleats, deck fittings, light fixtures, radios, stereos, or any
dis-similar metal where it contacts the hull. This will equalize any
stray
current in the boat and avoid "hot spots" where G.C. does its worst
work.

Zamack or chrome plated zinc cleats and fittings will deteriorate in
salt
water. If your boat is equipped with these fittings from the factory,
replace them.
--
Capt. Frank

__c
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www.home.earthlink.net/~aartworks
"CCred68046" wrote in message
...
I was reading a website from a manufacturer of all welded aluminum
boats.
There is a warning on the site that says:

"DO NOT GROUND YOUR ELECTRICAL WIRING DIRECTLY TO YOUR BOAT. Direct
electrical
contact on the boat will break down the weakest point of the
aluminum
and cause
holes in the boat. This is especially important if you are a
SAL****ER
Boater.
This is called ELECTROLYSIS and is not a defect in workmanship or
material."

How could you avoid this? The motor is bolted directly to the metal
transom
and is grounded, there is contact there. I checked my aluminum boat
with a VOM
and there is definately continuity between the boat and the motor.
Whats the
difference in letting the motor ground to the boat and not the
wiring?
What am
I missing here?