Shorepower and anodes

[Boomshanka]

Apologies if this is a daft question... I've got a shorepower cable on board that at the moment is running a small heater and dehumidifier. I'm about to connect up a battery charger to the shorepower... my engine (outboard), which is also connected to the battery via the alternator, lifts clear of the water in the marina and to my knowledge there are no other metal parts exposed below the waterline... question is... will connecting the battery charger to shorepower mean that I need anodes below the waterline or will anything on my GRP boat slowly dissolve and drop off?

 

[thompsoj]

Nothing in the GRP itself will dissolve but any metal touching water may. Anytime you have an engine, outboard or inboard, that is running a charger (gen or alternator) you need zinc's. If you don't have zinc's I'd definitely install one or more. Metal to consider that may be in the water is transducer, and impeller for speedometer both of which hook to your electrics so you can get galvanic action.

 

[William_H]

Assuming that you don't have any metal in the water (motor up) then you have no need for zinc sacrificial anodes. You don't need any earth connection at the boat just make sure you have good power extension cord. Make sure the dehumid /heater can't contact any moist carpets or wood. And if you really want to be safe don't leave the charger on when you leave the boat. olewill

 

[VicS]

The outboard should have its own anode (s) which will protect it while it is in the water. Nothing else to protect so no need, as stated by William H, for any other anodes.

(Anodes must be connected electrically to the items they are to protect so if you have no metal underwater then there is nothing to connect them to!!)

If there is any danger that the outboard will be in the water and if via the 12 volt system and the charger it is connected to the shore-power earth then a galvanic isolator in the earth might be worth considering.

Ideally if you are leaving the shore-power connected with charger, heater or dehumidifier running you should put in a basic fixed installation with circuit breakers and an RCD (using a "garage consumer unit" perhaps)

 

[qetoo]

I believe electrolysis occurs between different metals irregardless of whether there is battery charging or not. So if you have underwater metalic fittings you always need zincs if you are in salt water. I believe magnesium can be used in fresh water. If you have a shore power connection you also need to block stray currents from conducting through the ground safety wire connection. That source of electrolysis can be worse than galvanic electrolysis.

 

[roly_voya]

Second the idea that you dont need zincs, I ran a similar system for some time on a wooden boat with outboard with no problem but rather than just using a shorepower lead direct to equipment I fitted a double socket with intigrated RCD. Cost about £30 and worth it for the extra security. I would also recomend getting one of the plug in socet testers to check that the shorepower is correctly wired and has a good earth. Its not uncommon to find shorepower earths dodgy or none existant and with your setup you are relying on this for safety

 

[PlanB]

Do you have metal seacocks below the waterline?

 

[john_morris_uk]

[ QUOTE ]
Do you have metal seacocks below the waterline?

[/ QUOTE ]Even if you have, if they are good quality bronze and not connected electrically to anything you can ignore them. There has to be an electrical connection for there to be electrolysis and bronze seacocks usually survive very happily in isolation.

 

[VicS]

[ QUOTE ]
There has to be an electrical connection for there to be electrolysis and bronze seacocks usually survive very happily in isolation

[/ QUOTE ] In any case the copper alloys are towards the "noble" end of the galvanic series so it will be the less noble metals that will corrode not the bronze sea cocks and skin fittings.

 

[Boomshanka]

Many thanks for all the replies, much appreciated. I hadn't thought about the seacocks being metal and in contact with the water (great this forum eh?!?). The shorepower unit I have ( this one from Towsure) has a built in RCB so I think that should be alright... I think the consensus here is that I don' t need to worry about anodes (I checked the outboard and there is one on there for when it's in the water).

 

[VicS]

[ QUOTE ]
The shorepower unit I have

[/ QUOTE ] If that is adequate for your needs then that looks fine. The garage consumer unit I suggested was for simple but permanent installation. They have rcd and two mcb protected circuits, one at only 6A for lighting and one at 16A for supplying a small number of 240 volt sockets.