Re: [Amel Yacht Owners] AMEL MARAMU GROUNDING SYSTEM


DENNIS STULLER <svcheechako@...>
 

HI ROGER,

THANKS FOR THE INFORMATION. I SOMETIMES FEEL THAT I
KNOW MORE ABOUT BOAT GROUNDING SYSTEMS THAN I
UNDERSTAND. IN MY CASE THE PROPELLOR SHAFT IS NOT
INSULATED AND IT APPEARS THAT I HAVE SOME CORROSION
PROBLEMS AS EVIDENCED AT THE TRANSMISSION COOLER AND
ENGINE HEAT EXCHANGER. I AM GOING TO DIG DEEPER AND
CHECK CONNECTEDNESS AND CONDUCTIVITY OF THE SYSTEM. I
WILL LET EVERYONE KNOW WHAT I FIND.

REGARDS, DENNIS STULLER MARAMU #186


--- Roger Banks <roger.banks@...> wrote:

Hi Dennis

Yes, I've spent quite a bit of time looking at the
grounding systems
and there a few good articles in magazines and on
the internet, but
some how they never quite get down to specifics of
every situation.
There are four grounds which need to be kept
separate, subject to
certain approved interactions: AC, DC, HF, and
lightning. Regarding
the DC ground, which is the subject of your enquiry,
the logic not
many years ago was to connect together every metal
thru-hull, which
Amel have done elegantly with the grounding bus you
describe, which
connects to the zinc anodes mounted either side of
the rudder (at
least it's so on my Mango); this system still holds
good if you spend
your whole time in remote anchorages, but entering a
modern marina
exposes your boat to stray electrical currents from
and between other
boats (DC) and pontoon services (AC). This can set
up a galvanic
corrosion reaction, in which the current enters by
one thru-hull and
exits by another, taking with it some metal. This is
also a problem
where two or more metals are in contact in an
electrolyte, e.g. sea
water.

Therefore the common wisdom has altered since your
boat was built to
say that thru-hulls should not be linked together.
Bronze thru-hulls,
such as for toilet water intakes below the water
line, are considered
stable and may happily be left alone, i.e. not
connected via a strap
to any other thru-hull which would expose it to the
corrosion effects
described above.

There are some situations where connection is
unavoidable, such as
stainless steel (itself an alloy) prop shaft mounted
in bronze tube
and with copper propellor. It's essential to ensure
the grounding bus
is connected to both the prop shaft and its mounting
tube which, as I
recall, is visible inside the engine room, between
the engine and
stern gland. If you look further you will find that
the engine water
intake cock is connected by water to the raw water
manifold and to
the engine itself and, if I observe it correctly, to
the diesel
supply system via that fluid and to the fresh water
heater. Some of
the bus gets pretty inaccessible in these places.
I'm not 100% sure
of the electrical connectivity via fluids of some of
these items and
would be glad of contributions by others. It seems
to me that whether
the engine etc should be connected to the grounding
strap, and thus
the zinc anodes, is a question if there is more than
one connection
to the sea water, i.e. via the raw water intake and
what else? I
believe the prop shaft is isolated from the engine
by a flexible
coupling. The exhaust water exits above the water
line (as do all
basins and toilet water exit points), so does not
count. Thus if the
only connection point between the engine and sea
water is the raw
water inlet, it may be correct that the ground strap
was severed.

If your model of Maramu has a ground strap
connection to a keel bolt,
unlike my Mango where the rudder anodes are the
single point of
protection, then you may need to restore the
connection and make sure
the keel bolt is protected by an anode, but it may
be your analysis
of this is not correct.

Regards, Roger, Zorba, Mango 28


On 02/03/2006, at 1:15 PM, DENNIS STULLER wrote:


HAS ANYONE DELVED DEEPLY INTO THE AMEL GROUNDING
SYSTEM? IN THE
PROCESS OF CLEANING UP THE ENGINE COMPARTMENT ON
MY 1985 MARAMU HULL
#186 I HAVE FOUND THAT THE GROUND STRAP BETWEEN
THE ENGINE AND THE
GROUND BUS HAS BEEN SEVERED, APPARENTLY ON
PURPOSE. ALSO WHERE THE
GROUNDING BUSS PASSES IN FRONT OF THE ENGINE, IT
APPEARS AS IF THE
BUSS ORIGINALLY WAS EXTENED DOWN INTO THE BILGE
AND WAS BOLTED TO THE
KEEL BOLT AT THE BOTTOM OF THE BILGE. THIS MAKES
SOME SENSE, BUT ON MY
BOAT BOTH CONNECTIONS ARE SEVERED.

THANKS, DENNIS STULLER MARAMU #186 "CHEECHAKO"






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