metal bonding

If your a fisherman or woman needing earthworms to catch dinner, short of going to the bait store, here is another option.
Wait until it rains or wet your lawn overnight. Now, take a car battery, (2) 8 gauge cables, (2) 3' pieces of construction rebar and go out to your lawn.
Don't forget the hammer, drive the rebar stakes 24' apart and connect the negative cable to one of the bars and then to the negative post of your battery, do the same for the positive post. Within minutes earth worms burried in the ground between the two posts will begin to emerge, unharmed of course, now your ready to go fishing. The moisture in the soil act as a wire (conductor) between the two bars.
Same principal applies to thru-hull fittings, even if connected inside the boat with rubber hoses, weather bonded with wire internally or not, if not wired, the water around the hull becomes the conductor. I at least one major metal component, in this case the propeller shaft has a zinc attached we should be ok.
Marty Chin, BCC Shamrock


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Marty:
 
I agree, salt water becomes the ionic bridge between two metal conductors but unless the two pieces of metal are connected there is no current flow.
 
In the example cited, if there were no conductor between the two rebar stakes, the worms would stay in the ground.  Even if, the two stakes were connected with a wire, there would be no current flow because the two stakes have the same electro-negative potential.  By connecting a battery between the stakes, you are introducing an anode and cathode into the system and current flow occurs between the two stakes.  A similar principle has been tested to reclaim soil that was contaminated with metals.
 
In the case of the prop and prop shaft, the zinc is the anode, the bronze/steel is the cathode and the salt water becomes the ionic bridge.  Because the zinc is in contact with the bronze/steel, and has a lower electro negative potential than the cathode - prop and prop shaft, the zinc's mass decreases as it is converted to ionic zinc and your prop and prop shaft are protected.
 
I believe the most common cause of galvanic corrosion in boats is plugging into shore power.  Because the green wire is common to all boats connected to shore power,  zinc anodes on all the boats become common.  Therefore, if a boat next to yours does not have a zinc, the zinc on your boat also protects the boat next to you.  Hence, the zinc on your boat is depleted faster than expected and galvanic corrosion occurs.  This cause of galvanic corrosion can be prevented by installing a galvanic isolator or isolation transformer in the shore power circuit of your boat.
 
I have a basic understanding of this subject from my electro chemistry course work but would not consider myself an expert on the subject.
 
Rod
s/v IDUNA
 
 
----- Original Message -----
Sent: Wednesday, January 26, 2005 4:49 PM
Subject: [bcc] metal bonding

If your a fisherman or woman needing earthworms to catch dinner, short of going to the bait store, here is another option.
Wait until it rains or wet your lawn overnight. Now, take a car battery, (2) 8 gauge cables, (2) 3' pieces of construction rebar and go out to your lawn.
Don't forget the hammer, drive the rebar stakes 24' apart and connect the negative cable to one of the bars and then to the negative post of your battery, do the same for the positive post. Within minutes earth worms burried in the ground between the two posts will begin to emerge, unharmed of course, now your ready to go fishing. The moisture in the soil act as a wire (conductor) between the two bars.
Same principal applies to thru-hull fittings, even if connected inside the boat with rubber hoses, weather bonded with wire internally or not, if not wired, the water around the hull becomes the conductor. I at least one major metal component, in this case the propeller shaft has a zinc attached we should be ok.
Marty Chin, BCC Shamrock

The best way to protect your boat is with an isolation transformer - which has a floating ground.
Kirk
----- Original Message -----
Sent: Wednesday, January 26, 2005 7:38 PM
Subject: Re: [bcc] metal bonding

Marty:
 
I agree, salt water becomes the ionic bridge between two metal conductors but unless the two pieces of metal are connected there is no current flow.
 
In the example cited, if there were no conductor between the two rebar stakes, the worms would stay in the ground.  Even if, the two stakes were connected with a wire, there would be no current flow because the two stakes have the same electro-negative potential.  By connecting a battery between the stakes, you are introducing an anode and cathode into the system and current flow occurs between the two stakes.  A similar principle has been tested to reclaim soil that was contaminated with metals.
 
In the case of the prop and prop shaft, the zinc is the anode, the bronze/steel is the cathode and the salt water becomes the ionic bridge.  Because the zinc is in contact with the bronze/steel, and has a lower electro negative potential than the cathode - prop and prop shaft, the zinc's mass decreases as it is converted to ionic zinc and your prop and prop shaft are protected.
 
I believe the most common cause of galvanic corrosion in boats is plugging into shore power.  Because the green wire is common to all boats connected to shore power,  zinc anodes on all the boats become common.  Therefore, if a boat next to yours does not have a zinc, the zinc on your boat also protects the boat next to you.  Hence, the zinc on your boat is depleted faster than expected and galvanic corrosion occurs.  This cause of galvanic corrosion can be prevented by installing a galvanic isolator or isolation transformer in the shore power circuit of your boat.
 
I have a basic understanding of this subject from my electro chemistry course work but would not consider myself an expert on the subject.
 
Rod
s/v IDUNA
 
 
----- Original Message -----
Sent: Wednesday, January 26, 2005 4:49 PM
Subject: [bcc] metal bonding

If your a fisherman or woman needing earthworms to catch dinner, short of going to the bait store, here is another option.
Wait until it rains or wet your lawn overnight. Now, take a car battery, (2) 8 gauge cables, (2) 3' pieces of construction rebar and go out to your lawn.
Don't forget the hammer, drive the rebar stakes 24' apart and connect the negative cable to one of the bars and then to the negative post of your battery, do the same for the positive post. Within minutes earth worms burried in the ground between the two posts will begin to emerge, unharmed of course, now your ready to go fishing. The moisture in the soil act as a wire (conductor) between the two bars.
Same principal applies to thru-hull fittings, even if connected inside the boat with rubber hoses, weather bonded with wire internally or not, if not wired, the water around the hull becomes the conductor. I at least one major metal component, in this case the propeller shaft has a zinc attached we should be ok.
Marty Chin, BCC Shamrock