Re: Mango Grounding
Roger Banks <roger.banks@...>
Hi Michael
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Nice to hear from a Mango owner; there don't seem to be too many of us participating in the forum. I wouldn't describe myself as an expert, but am happy to help you with some suggestions. The zincs rapid disappearance definitely indicates something is wrong. After 18 months my rudder anodes were slightly used, and of course I changed them anyway. I was puzzled about why the only anodes are those on the rudder and was worried how I could place a suitable anode to protect the propshaft and engine. Investigation revealed that the rudder anodes are connected to the grounding strap which can be seen emerging by the rudder post (under the aft bunk), passing along the locker under the aft bunk, then appearing again in the engine room close to the prop shaft, tacked along the bilges under the engine, across to the engine earthing point, and so on through the boat. Thus no other zincs should be required. I've tested this with a multimeter and can report there was no resistance between the rudder anodes and the grounding strap sampled at several places through the boat. Your situation indicates that there is regular electrical activity through your anodes into the sea water; perhaps also your anti- fouling is copper-based (as is common), which might be producing the paint blistering you describe. It's important to recall that the DC grounding system to the anodes is intended to connect your anodes together for protection from galvanic corrosion, i.e. it is not necessary or desirable in the context of your DC battery circuits, particularly the services side. With regard to the services side, unlike a car, where a single wire leads to, say, a lamp and the return wire is grounded to the car body, on a boat all DC circuits should return via a negative cable to the battery (bearing in mind that many services cables lead back to the common earthing point in the electrical cupboard above the galley, and thence by a heavy-duty cable to the service batteries). The engine, being an automotive component, does have a number of electrical contacts, mainly sensors, which run to earth via the engine casting; however these circuits are completely separate from the services-side circuits and, when the engine batteries are isolated, are inert. In operation there should be no reason for earth leakage unless there is a resistance or break in the route back to earth, so perhaps you should check your main fuse (mounted on a tray at the aft end of the engine) and all connections on the route from there back via the starter-motor to the batteries (on my boat it's to a services battery negative post and thus via heavy-duty cable to the engine batteries); check all the connections around the starter-motor especially as inability of the commutator cranking current to return to battery negative would result, presumably, in a heavy discharge via the grounding strap into the sea (consistent with your description); similarly if the services- side to engine battery negative connection is not good. (Did you do your protection check also while the engine was running?) If in doubt, clean or replace all these cables until your problem disappears. The services and engine battery banks should have completely separate electrical wiring systems except for the one heavy-duty cable direct between the battery bank negatives. There should be one position only at which the DC system interconnects with the grounding strap, which is at the engine earthing point; on my Perkins 4.236 this is forward on the port side of the engine. Thus, when the engine batteries have been isolated, which is presumably most of the time, there is no cause for electricity to be circulating via the engine into the grounding strap and so on to the rudder anodes. You may want to check your wiring carefully to see if any other DC/ grounding interconnects have been made; check that each grounding system (DC, AC, HF, lightning) is separate from the others, subject to sensible interconnects, e.g. if the HF counterpoise is grounded to the engine or the grounding system, there needs to be a gap of one tenth of an inch (by fastening to a piece of phrenolic or electrical circuit board), bridged by suitable capacitors (which are transparent to HF but block DC); consider cutting the grounding strap from the aft head intake and from any other "passive" thru-hulls below the water line (I'm afraid I'm not familiar with a MaxProp). I addressed this sort of thing in my previous posting. They're great boats but in all these years many pairs of hands have been doing stuff. I'm amazed at what I find even professionals have done wrong. For instance, only recently in hunting down the cause of excess gassing in the service batteries, I found the regulator on some new solar panels I had installed last year is undersized; and just last week I found through detailed enquiry on the manufacturer's website that the regulator on my wind generator is under-sized too. I do everything myself now! Have fun and don't forget to report back if you have a success. Regards, Roger, Zorba, Mango 28
On 03/03/2006, at 1:40 AM, Silkair@aol.com wrote:
Roger
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