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Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems
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  #1  
Old 04-21-2009
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Bonding through-hulls?

I've been re-working lots of stuff on my boat (currently on the hard) and one thing I've noticed is that there was ground wire which had previously bonded together all the through-hulls (and engine, dynoplate, mast conductors, etc.)

I'm guessing that the prior boat owner disconnected the through-hulls when he replaced them. I'm trying to figure how important it is to re-connect them, and if so, what I need to connect. I know that salt water can conduct a little, so there could be an electrical connection through the water in hoses.

Just the same I'm trying to remind myself what I'm actually grounding them to (other than the shore-power safety ground and DC ground), and how this will really help galvanic corrosion. Since there is a plastic isolation coupler on my shaft, the prop shaft probably isn't bonded to the engine/boat ground anyhow.

I DO intend to make sure that my masts are grounded for lightning protection. No questions there.
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Old 04-22-2009
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This is a big question that I'm sure has been addressed in depth in the past.
My feeling is that I will not re-bond my thru-hull fittings.
You should not assume that your shaft and engine are isolated from each other just because you have the plastic coupler....there are bonding straps that are often used to bond through this coupler.
Usually one on each side of the coupling and often quite flush, so have a close look.
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Old 04-23-2009
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Quote:
Originally Posted by kaluvic View Post
This is a big question that I'm sure has been addressed in depth in the past.
My feeling is that I will not re-bond my thru-hull fittings.
You should not assume that your shaft and engine are isolated from each other just because you have the plastic coupler....there are bonding straps that are often used to bond through this coupler.
Usually one on each side of the coupling and often quite flush, so have a close look.
I still don't know what to do about the through-hulls either.

I was just saying that I'm not sure if the engine (grounded) is bonded to the shaft/prop or not. (Next time I'm nearby, I'll check it out. It is a PYI 4-bold 1 inch model, I believe) In any case, it is just one more way the bonding system could be incomplete.
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Old 04-23-2009
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The way my couplers bond straps are set up (recessed/countersunk) I don’t think I could visually confirm that they are installed, the end of the bond straps may look just like the edge of the washers (see the picture in the below link)...you may have to check with a meter to confirm.

PYI - Flexible Shaft Couplings
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Old 05-01-2009
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ditch the bonding, period. look at it this way - the whole point of bonding is to eliminate difference in electrical potential between different metallic elements below the waterline. We are talking millivolts. Accordingly, it only takes a few milliohms of resistance to change the electrical potential between components. I'm sure you've seen corrosion on bonding wires and bronze thru-hulls. it would be different if there was a lug on these fittings so bonding wires could be properly soldered, but usually they are attached with hose clamps. within a few months of bonding as system like this you can bet everything will be at a different electrical potential anyway. keep an eye on zincs and you should be good to go.
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Old 05-02-2009
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Electrolysis cannot occur on an isolated piece of metal in salt water. It is all at the same voltage but if it is isolated no current can flow so there is no electrolysis. When it is connected to another piece of metal, ESPECIALLY if the other piece is a different metal, you just created a shorted battery and electrolysis will start. By following the wrong advise and bonding everything in the boat you are creating batteries where it is unnecessary and making electrolysis problems worse.
Only bond underwater items that are showing symptoms of electrolysis. Once you bond it unnecessarily you have CREATED the circuit rather than DISCONNECTING it. You are now stuck with providing Zincs since you have removed the first line of protection.
Although some through hulls appear to be isolated due to sitting in fiberglass and using non-metallic tubing, they quite often are not and WILL need bonding. For example the raw water cooling inlet for an inboard engine is in fact connected to the engine block by the salt water in the tubing and may need bonding so the current flows though copper rather than the water and in/out of the through hull.
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Old 05-02-2009
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sure, but as you say, once bonded - imperfectly bonded - you create a circuit which will almost certainly have different voltage potential between elements. if the connection is perfect you have essentially one piece of metal, but maintaining that perfect connection is almost impossible.

the biggest determinant of the need for bonding thru-hulls is if corrosion is apparent. my raw water input thru-hull has never needed bonding and i suspect that the pencil anode in the heat exchanger takes care of it.
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Old 05-02-2009
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My surveyor mad a big deal on one disconnected bonding wire. The insurance company expected it to be reconnected.
Right or wrong, they play the tune, I just dance.
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