Re: [Amel Yacht Owners] AMEL MARAMU GROUNDING SYSTEM
Roger Banks <roger.banks@...>
Hi Dennis
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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:
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