I know, I know -- this has been discussed before. Still, the thru-hulls in our boat are currently bonded and I'm looking for opinions: I've read a lot of conflicting views on the value and advisability of bonding thru-hulls. Sabre bonded the thru-hulls on our 1978 S28 to the ground system & keel. ABYC only requires bonding of thru-hulls if they are attached to galvanically incompatible hulls (e.g. aluminum or steel), or if they are installed at a location that's normally under the level of the bilge water (H-27.7.5.1 and H-27.7.5.2). If the thruhull is all of one type of metal, there won't be any galvanic action. They certainly don't need to be protected from lightning -- they are underwater and will have the same electrical potential as the surrounding seawater. I also understand that if your have your thruhulls bonded, and if you're in a "hot" marina, the thru-hulls can serve as an attractive conduit for the stray underwater current -- the electricity goes in one thru-hull and out the other. This would be a very bad thing. Thoughts?
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Bob Howie
You seem to understand it pretty well
I think you have a good understanding of how this works. I recently asked my yard about this same topic since my yard has a lot of experience with boats of all types and large yachts. They said it's pretty much not worth the effort, principally because of the way bonding can actually do the opposite of what is intended as you are apparently aware. They said generally speaking bonding is not really worth the effort on smaller boats; that using zincs and replacing them as well as using sacrificial anodes hung over the side of the boat work pretty well in keeping stray current away from the boat. I do that and it works pretty well for me.
I think you have a good understanding of how this works. I recently asked my yard about this same topic since my yard has a lot of experience with boats of all types and large yachts. They said it's pretty much not worth the effort, principally because of the way bonding can actually do the opposite of what is intended as you are apparently aware. They said generally speaking bonding is not really worth the effort on smaller boats; that using zincs and replacing them as well as using sacrificial anodes hung over the side of the boat work pretty well in keeping stray current away from the boat. I do that and it works pretty well for me.
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R.W.Landau
are the hoses connected to the thru-hulls
Rubber? Do they have metal in them? If they are rubber with no metal, disconnect the bonding to the thru hulls. Don't get me wrong here, I did not say not to keep a single grounding area to the exterior ( water) of the boat. An electric circuit is only complete when the switch is on and electricity can pass throught. Yes, dissimilar metals is a problem, but not if they are not connected electrically. If you connect them electrically, your have completed a circuit and your least noble metals will pay the price. Please remember that (I think) grounding of ac, dc, lightning, and bonding should have a common point of ground to water. This eliminates potentials and give a place to ground misguided electric. I think your assumptions are correct. r.w.landau
Rubber? Do they have metal in them? If they are rubber with no metal, disconnect the bonding to the thru hulls. Don't get me wrong here, I did not say not to keep a single grounding area to the exterior ( water) of the boat. An electric circuit is only complete when the switch is on and electricity can pass throught. Yes, dissimilar metals is a problem, but not if they are not connected electrically. If you connect them electrically, your have completed a circuit and your least noble metals will pay the price. Please remember that (I think) grounding of ac, dc, lightning, and bonding should have a common point of ground to water. This eliminates potentials and give a place to ground misguided electric. I think your assumptions are correct. r.w.landau
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bill walton
Phil your help is needed
How about trying to line up a guest forum on this subject. I think we'd all be able to benefit. I'm a bit confused because I was told that it was better to have all metal bonded in order to keep all at same potential. This forces the zinc to go away rather than any other metal. The only way to insure this, is to have a bonding system connected to all items in contact with the sea.
How about trying to line up a guest forum on this subject. I think we'd all be able to benefit. I'm a bit confused because I was told that it was better to have all metal bonded in order to keep all at same potential. This forces the zinc to go away rather than any other metal. The only way to insure this, is to have a bonding system connected to all items in contact with the sea.
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Doug T.
Dissimilar metals
Galvanic corrosion is only a problem when you have dissimilar metals in contact with each other AND when they are both in an electrically conductive solution (e.g. seawater). Like your bronze prop and your SS shaft. Or if you have a bronze thruhull connected to a copper or brass or steel pipe/hose in your bilge. (Yuck!) The different potentials in the metals, when immersed in the conductor, create a galvanic cell (a battery). Current flows from one to the other and one of the metals loses electrons. And eventually, mass. You add a zinc to the "cell" because it's loses electrons much more readily than most other metals. (For a more visible example, check out the corrosion on an old aluminum mast with stainless steel fittings. I saw a mast last year while boat shopping where the SS gooseneck had almost eaten all the way through the mast! No, we didn't buy that particular boat!) Anyway, if you have an all-bronze thru-hull, it's not going to corrode all by itself. At least, not galvanically. I see no purpose in connecting them to all of the other metal on the boat through bonding.
Galvanic corrosion is only a problem when you have dissimilar metals in contact with each other AND when they are both in an electrically conductive solution (e.g. seawater). Like your bronze prop and your SS shaft. Or if you have a bronze thruhull connected to a copper or brass or steel pipe/hose in your bilge. (Yuck!) The different potentials in the metals, when immersed in the conductor, create a galvanic cell (a battery). Current flows from one to the other and one of the metals loses electrons. And eventually, mass. You add a zinc to the "cell" because it's loses electrons much more readily than most other metals. (For a more visible example, check out the corrosion on an old aluminum mast with stainless steel fittings. I saw a mast last year while boat shopping where the SS gooseneck had almost eaten all the way through the mast! No, we didn't buy that particular boat!) Anyway, if you have an all-bronze thru-hull, it's not going to corrode all by itself. At least, not galvanically. I see no purpose in connecting them to all of the other metal on the boat through bonding.
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Peter Brennan
Pink strut
All metal on our boat (O'Day 37) is bonded. The boat came that way. The grounding plate that forms the condenser for the refrigerator is even connected to battery negative. Two years ago when some work was done on the engine somebody neglected to reconnect the bonding wire attached to the bronze shaft and strut. When we hauled, there were no barnacles on shaft, strut and propeller as there usually are. But the strut had pink spots indicating dezincification. The zincs on the shaft did protect the shaft and prop and they were completely gone. We reconnected the bonding wire and things were as usual when we hauled this time. I believe in bonding.
All metal on our boat (O'Day 37) is bonded. The boat came that way. The grounding plate that forms the condenser for the refrigerator is even connected to battery negative. Two years ago when some work was done on the engine somebody neglected to reconnect the bonding wire attached to the bronze shaft and strut. When we hauled, there were no barnacles on shaft, strut and propeller as there usually are. But the strut had pink spots indicating dezincification. The zincs on the shaft did protect the shaft and prop and they were completely gone. We reconnected the bonding wire and things were as usual when we hauled this time. I believe in bonding.
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