Bonding System - Do I Need It ?

[bony]

Hello,
I need some advice on whether I should fit a bonding system for my boat's metallic parts. I have been reading a fair bit about the subject on the web and have learned that a fibreglass boat moored in salt water should have it's metallic parts connected together with copper wire to help prevent electrolysis and corrosion.

My boat is a 20 foot F/glass fishing boat powered by an inboard Yanmar 2qm15 diesel engine. I am doing a complete rewire of the boat's electrical system and I know that bonding and grounding are different systems and that the bonding should be kept separate from the boats electrical grounding. But I am confused as to whether I need to go to the trouble of bonding at all because the articles I've read advise bonding "if the boat is connected to shore power while moored" .

My boat has a permanent mooring at a jetty berth alongside several other boats. The jetty itself is not powered and therefore none of the boats in the vicinity will be connected to shore power. I will have zinc anodes fitted to my prop shaft and rudder, so do I really need to bother with bonding for my boat or not?

Thanks,
bony

[bruce smith]

It may protect the boat against lightning strikes.
It may effect your neighbors boats in a negative way.
20 ' fishing boat, how many fittings have you got?
short opinionated answer, no

[Andina Marie]

Electrolysis is caused when two metals of different types are in water and connected together. Connecting them together forms a battery and current flows causing metal to be removed from the most "active" metal.

In many instances such as a bronze propeller on a stainless shaft the two metals are connected together (bonded) and you have to provide a "sacrificial" anode (zinc) so it gets eroded instead of your expensive equipment.

Despite all you read about bonding underwater metal I strongly disagree. An isolated piece of metal that is not connected can't form a battery. Once you bond it to everything else (including the dock and other boats) you now INVITE electrolysis. My suggestion is to monitor all underwater exposed metal on only bond if you see evidence of electrolysis. DON'T FIX IT IF IT AINT BROKE.

Keep in mind that although some items appear to be isolated they may not be. For example a raw water intake and filter connected to the engine by a non-conducting hose are actually connected together by the salt water inside they tubing. Bonding it to the engine will make sure there is no electrolysis action between the through hull and the water pump on the engine.

[Cheechako]

I say no.

[Jentine]

The simple answer is NO. The complex answer is NO!!!!!!!!!!!! Spend your money on useful toys.

[bony]

Thanks fellas, it would appear that the nays have it. I wasn't sure if it was necessary or not and now realise I was stressing about it needlessly.

I will bond the r/w intake ball valve though because when I bought the boat the original valve was almost completely eaten away.

Many thanks to you all for the help on this matter, much appreciated.

".....Spend your money on useful toys"

Now that's the kind of advice I really like.

Cheers,
bony

[Wotname]

Just for the sake of completeness - bonding IS important on a traditional wooden boat.

As Andina points out, two dissimilar metals joined together electrically in the presence of sea-water creates a cell and current flow.

The problem with a wooden hull is that the damp wood connects the metals electrically together thus forming the cell. The current flows through the wooden hull between the metal fittings and destroys the cellular structure of the timber. The bonding wire was used to allow the current to flow through the wire rather than the wood.

The most "active" metal fitting was still eaten away but the wood remained unaffected.

IMO, such bonding has no place in a fibreglass hull but remains important for a wooden hull.

[sdowney717]

bonding IS important on a traditional wooden boat.

No dont bond wooden boats. The bronze forms a battery with the wood and the wood fizzles away. Takes a long time. People who restore old boats hate bonding systems especially on wood boats. Read about it on the wooden boat forum.
http://forum.woodenboat.com/showthre...ding-questions

Wet wood also conducts electricity. Screws holding planks will become part of a giant underwater battery. everything will dezincify and delignify.
Fuel tanks must be grounded, I left my bonding intact on fuel tanks, metal shaft logs back to engine block and disconnected everything else.
Rip it out is safest so future owners wont be tempted to hook it up again.

Yes joining all your underwater metals forms a big battery. All your underwater metals wear down, the less noble will go faster. Aluminum can turn into swiss cheese if there are stray currents in the water.

[sdowney717]

Bonding and Corrosion
Hit by lightening and blew out all the thru hulls cause they were bonded, wow. If no bonding to the mast then perhaps only one would have vaporized or maybe none.

Wood Boats and Zinc

A special mention needs to be made regarding wood boats. I mentioned that we bond zinc to our already bonded bronze-stainless prop and shaft. You need to be careful with a wood boat because in the process of protecting the metal, you are eating away the wood. The zinc-bronze electrochemical reaction creates hydroxyl ions around the zinc. These are corrosive to wood and will eat the wood leaving only the cell walls. I have taken to putting only a single zinc on my prop shaft as we were getting too much wood damage when I had 2 zincs. At one time the yard put a large zinc plate right on the wood with a wire over to some metal. I had significant wood damage around that zinc so we didn't replace it letting the 1 inch bronze rudder shaft protect itself for another 50 years as it had for the first 50. The moral is that on a wood boat, zinc is good and zinc is bad. You need to find a balance. This is, of course, another reason not to bond all your through hulls thinking your zincs will protect them as you will then be eating away the wood right around your through hulls, a particularly bad idea.

"A sailboat was hit here by lightning and sank 100 yards out in the channel, it sank in a few minutes. When they brought it in all the through hulls had been blown out, I looked in it, the mast and all the thru hulls were bonded."

[sailinman]

bonding is connected to grounded parts, just at a different location...

[Wotname]

Originally Posted by sdowney717

Bonding and Corrosion
Hit by lightening and blew out all the thru hulls cause they were bonded, wow. If no bonding to the mast then perhaps only one would have vaporized or maybe none.

[/quote]Wood Boats and Zinc

A special mention needs to be made regarding wood boats. I mentioned that we bond zinc to our already bonded bronze-stainless prop and shaft. You need to be careful with a wood boat because in the process of protecting the metal, you are eating away the wood. The zinc-bronze electrochemical reaction creates hydroxyl ions around the zinc. These are corrosive to wood and will eat the wood leaving only the cell walls. I have taken to putting only a single zinc on my prop shaft as we were getting too much wood damage when I had 2 zincs. At one time the yard put a large zinc plate right on the wood with a wire over to some metal. I had significant wood damage around that zinc so we didn't replace it letting the 1 inch bronze rudder shaft protect itself for another 50 years as it had for the first 50. The moral is that on a wood boat, zinc is good and zinc is bad. You need to find a balance. This is, of course, another reason not to bond all your through hulls thinking your zincs will protect them as you will then be eating away the wood right around your through hulls, a particularly bad idea.

"A sailboat was hit here by lightning and sank 100 yards out in the channel, it sank in a few minutes. When they brought it in all the through hulls had been blown out, I looked in it, the mast and all the thru hulls were bonded."[/quote]

Not so fast, the article does not say the through hulls failed because they were bonded. It simply notes that they were bonded.

[Wotname]

Originally Posted by sdowney717

No dont bond wooden boats. The bronze forms a battery with the wood and the wood fizzles away. Takes a long time. People who restore old boats hate bonding systems especially on wood boats. Read about it on the wooden boat forum.
electrolysis, wiring and bonding questions

Wet wood also conducts electricity. Screws holding planks will become part of a giant underwater battery. everything will dezincify and delignify.
Fuel tanks must be grounded, I left my bonding intact on fuel tanks, metal shaft logs back to engine block and disconnected everything else.
Rip it out is safest so future owners wont be tempted to hook it up again.

Yes joining all your underwater metals forms a big battery. All your underwater metals wear down, the less noble will go faster. Aluminum can turn into swiss cheese if there are stray currents in the water.

This really depends on what you are trying to save; the metal or the wood.

My understanding of the chemistry indicates that as far as wooden hulls go, bonding saves the wood but causes the metal to fail faster while not bonding will slow the electrolysis of the metal but will also cause long term damage to the wood. Either way, the metal will be lost. I understand it is easier to replace through hulls than planks.

I don't see how joining the the underwater metals forms a big battery. As I understand it, a battery is formed by the presence of dissimilar metals in an electrolyte. In this instance the dissimilar metals exist and the electrolyte is the sea water. The battery exists whether the metals are mechanically joined or not.

Joining them (by a bonding wire) allows the battery to discharge via the wire. The battery will continue to discharge until the least noble metal is eaten away (ie deposited onto the more noble metal) and the battery no longer exists; so yes, the bonding will speed up the wasting of the metal. In fact it will probably significantly speed up the electrolysis of the metals.

However if you remove the bonding wire, the battery will discharge through the wet wood thus causing damage to the timber. Of course the resistance of wet wood is much higher than that of the bonding wire so the current flow is much lower. This means the battery will take much longer to discharge, ie. much longer before the least noble metal is completely eaten away; so by removing the bonding, you have slowed down the wasting of the metal but have allowed the timber to be destroyed in the process. Note the end result to the metal is same, it will be completely destroyed either way.

Perhaps if one is interested only in the shorter term view of saving the through hulls etc, don't bond. The damage to the timber will be slow, probably not picked up in a survey (unless the through hulls are removed) and will become some future owners problem.

In my view, neither option will have an affect on the fastenings one way or the other. They will will be having their own little electrolysis problems to deal with in their own little circuits.

Disclaimer - I could be wrong but if so, what is the chemistry that demonstrates why?

[bruce smith]

Bond a wood boat? You can't bond every single screw , nail and bolt , so it would not be a good idea. You would sacrifice the vessel to save the fittings.

[Wotname]

Originally Posted by Andina

Electrolysis is caused when two metals of different types are in water and connected together. Connecting them together forms a battery and current flows causing metal to be removed from the most "active" metal.

In many instances such as a bronze propeller on a stainless shaft the two metals are connected together (bonded) and you have to provide a "sacrificial" anode (zinc) so it gets eroded instead of your expensive equipment.

Despite all you read about bonding underwater metal I strongly disagree. An isolated piece of metal that is not connected can't form a battery. Once you bond it to everything else (including the dock and other boats) you now INVITE electrolysis. My suggestion is to monitor all underwater exposed metal on only bond if you see evidence of electrolysis. DON'T FIX IT IF IT AINT BROKE.

Keep in mind that although some items appear to be isolated they may not be. For example a raw water intake and filter connected to the engine by a non-conducting hose are actually connected together by the salt water inside they tubing. Bonding it to the engine will make sure there is no electrolysis action between the through hull and the water pump on the engine.

I agree except in the special case of traditional wooden hulls. The metals cannot be isolated due to the damp timber so other measures have to taken and one has to chose the lesser of two evils.

Of course it is possible to bed all underwater metal fittings in epoxy etc but that can't be considered traditional.

[Wotname]

Originally Posted by bruce smith

Bond a wood boat? You can't bond every single screw , nail and bolt , so it would not be a good idea. You would sacrifice the vessel to save the fittings.

Exactly, and bonding the through hulls has no (or very little) effect on the fastenings.

Bonding through hulls on wooden hulls does not save the metal, it saves the timber!

At least it does IMO