Bonding underwater fittings

When it comes to electrical systems aboard boats, Arild Jensen knows his stuff. Here's where to ask the simplest or most complex questions about marine electrics.

Bonding underwater fittings

Postby rudysechez » Mon Feb 15, 2010 4:53 am

Arild, I'm just finishing replacing all the thru-hulls and seacocks on a boat whose previous thru-hulls were damaged by electrolysis. In fact, the boat sunk because of one thru-hull that fell apart. The bonding wires were very poorly attached and corrosion was rampart in their connections. Several weeks ago, I read an article where, I believe, it was stating that the ABYC has now reversed its position on bonding underwater fittings and is now saying that they should not be bonded; they should remain isolated. Did I misunderstand? As the new thru-hulls are in, I need to know if these new bronze fittings should be bonded. (The owner did not want to replace with Marlon.) Thanks.
Briney Bug, Panama City, Fl
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Re: Bonding underwater fittings

Postby elnav » Mon Feb 15, 2010 11:18 am

To bond or not to bond has been a controversial subject for at least four decades that I know of. I'm glad to see ABYC finally see the light. Connecting the thru hull fittings together was a cheap way to get a connection to the water for the electrical AC system. Should you choose not to bond I recommend a square foot (surface area) of copper sheet metal placed on the outside of the hull somewhere. Connect to the inside Green safety ground wiring by using a sealed and caulked thru bolt. Do whatever it takes for the bolt not to leak. For sailboats a metal keel would be a good substitute. This also serves as the lightning ground point. if you do that, make sure the lightning ground wiring follows a straight line as closely as possible.
In the old days you could screw or nail the copper to the wood planking. Bonding the copper to fiberglass using an adhesive like 5200 would work but be sure the connecting thru bolt makes a solid connection.solder it in place if possible before you install the plate
Arild Jensen
Custom electrical design for cruising boats
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