Electrical Bonding

[dbdaniel]

The prev owner of my 42p, for whatever reason, decided to remove some of the bonding wires on the boat. All of the thru-hulls and the fuel tank are not bonded. I'm a new boat owner and it didn't dawn on me to look for safety features like this until I weathered my first severe lightning storm. What guage wire would you fine folks recommend I use to hook all these bad boys up to the negative doohickie in the engine room?

Thanks for any help.

 

[Don S/V ILLusion]

This is a more complex issue than simply yes/no

Blanket statements such as 'all underwater metal should be bonded' or 'all underwater metal should be unbonded' does not take into account the individual situation the boat may be in. There are three types of corrosion underwater metals are subjected to---Electrolytic, Galvanic, and Stray current. Bonding underwater metals (and installing a zinc) will cure/prevent the first two types of corrosion but will cause or speed up the last. It is best to find out what type of corrosion your boat is experiencing before deciding on the cure and if you are not experiencing a problem, leave well enough alone.
Galvanic & Electrolytic (Stray Current) corrosion are two similar, yet different ,types of corrosion.

Galvanic corrosion results when two dissimilar metals, of sufficiently different potentials (about 0.1 V on the galvanic series) (a galvanic couple can also occur within regions of a single alloy), are electrically connected (bonded; deliberately or not), and immersed in a common electrolyte (water). The same electro-chemical reaction creates the current flow in a storage battery.

Stray Current (or Electrolytic) corrosion results when an applied current flows through immersed conductive materials, other than an intended electrical circuit.
Stray currents can come from an outside source either internal or external to your boat. Internal sources involve a short in your boat’s wiring system, such as a poorly insulated wire in the bilge, an electrical accessory that may be improperly wired, or a wire with a weak or broken insulation that is intermittently wet.
External sources are most often related to shore power connections, or other boats on the dock .



BONDING STRAPS
Although copper straps look impressive they are totally unnecessary. At most, the wire only carries a few milliamps and there is no concern for voltage drop so the copper only needs to be heavy enough to resist deterioration from oxidation. A 10 gauge copper wire is more than adequate. I use non stranded 10 gauge bare copper wire for my installations, being careful to secure it so it is not subject to flexing from boat motion. Non stranded wire has much less surface area and avoids the cavities between the strands where moisture and corrosion/oxidation can progress.


Electrolysis only happens when two dissimilar metals are immersed in an electrolyte and connected together. The dissimilar metals have different electrolysis voltages so if you connect them together current flows through the connecting wire one direction and through the water the other. As the current leaves one metal to travel to the other, it causes metal to come off one surface and be deposited on the other like battery plates so the higher voltage metal suffers electrolysis. Electrolysis can also occur when an adjacent structure or boat is injecting DC current into the water and that current goes in one end of your boat and out the other on its way to the destination. This can cause electrolysis even though your boat is not an offender.


There are basically 2 ways to reduce electrolysis. The PREFERABLE one is to DISCONNECT the electrical circuit. If this can't be done, the second method is to provide a sacrificial anode (Zinc) so it deteriorates rather than your expensive equipment.


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. If it ain't broke, DON'T fix it. 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.



Keep in mind that the zinc will CREATE electrolysis (favorable electrolysis since the zinc is being eaten up). Putting zincs where they were not needed will still cause the zincs to erode away since they create the battery situation where none may have existed.



Generally, electrolysis problems are created by the shore power connection. You could theoretically disconnect the ground connection in the shore power and avoid electrolysis (and in some cases this is a solution) but ABYC regulations require the AC ground be connected to the DC ground so an electrical fault on the boat won't electrocute swimmers in the vicinity.
When you connect your underwater metal to the shore power ground you have "bonded" with every other boat on the docks who have the same connection. Now electrolysis currents are free to flow anywhere in the marina and it only takes one boat with a 12 volt DC leakage to eat up every boat within a wide radius even though the offender has zero electrolysis evidence.
Your protection is a Galvanic Isolator in the ground connection of the shore power lead.. Any Galvanic Isolator that meets AYBC specifications will do - they are not rocket science and extremely reliable.

 

[Rick D]

Re: This is a more complex issue than simply yes/no

Very nice reply, Don. That's what keeps this board valuable.

 

[Franklin]

Hunter doesn't bond them for a reason. The reason is that they feel (And I agree) it's more important to protect them from stray current by keeping them isolated, then it is to protect them from galvantic corrision, as a stray current can eat away at your thru hulls much much faster, as in weeks, compared to the years of galvantic corrision.

Why? Because if you have 110 volt leak into the ground and the ground is bonded to the engine, then there is going to be so much resistance at where the water meets the zinc, that the rest of the current that can't flow through there is going to flow through your thru hulls. And if the 110 volt isn't grounded at the engine but the thru hulls are still bonded, then that opens up current floating through the water from the stern, up into the shafe, along the bonded wire, and back out into the water via thru hulls taking part of your thru hull with it. Remember, current always takes path of least resistance.

Hunter also doesn't connect it's 110volt ground to the engine for the same reason. It is more important to keep the 110 volt system away from the prop as a short in the boat can eat away the zincs in no time and then the prop when it's coming from the 110 volt. It also exposes your boat's prop to other boat's and dock 110 volt problems. Hunter believes the dock should provide a good ground for the 110 volt system.

The only downside to this is, if the dock doesn't properly ground and neither do any other boats and there is a stray 110 volt current, you are at danger if you touch something that is charged and something grounded. Usually, that would be the shrouds and the dock, like getting off the boat and holding onto the shrouds, however, this is the reason why hunter doesn't bond the mast to the engine either. So even if there is a stray current, you shouldn't ever get stung and sooner or later it's going to find a way to ground safely. Do note that Hunter does bond the mast to the keel bolts to protect the hull from a lighting strike.

Summary, Hunter believes this is the way it's supposed to be and I agree with them. Do not bond your thru hulls to the engine, or the mast to the engine or the 110 volt ground. Just replace your thru hulls once every 10 years...maybe replace them with plastic ones if you are comfortable with them. Less weight, that's for sure.

Hunter has been building boats for a very very long time and they keep improving, or at least trying new things. Some things they have perfected and I believe this is one of them.

It's also a good idea to get one of those spacers (forget the techincal term) that goes between the two cuplings where the shaft meets the transmittion. That will stop all outflow of electricity through the shaft and you will not have to worry about electrolysis destroying your prop as long as you replace your zincs once a year.

Speaking of zincs. Always put two on. The first one is a warning as one will eat through first and fall off. If you only have one after a few months, you have a problem but still have another protecting the prop while you figure out what to do about it.

 

[Franklin]

"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."

Not really true. The salt water acts like the acid in a battery, so the different metals in the water will provide a electrical current between them. However, this current is very small so it's not going to eat a strong metal like a thru hull quickly.

 

[Don S/V ILLusion]

Franklin

This is a distinction without a difference.

Your statement
"Not really true. The salt water acts like the acid in a battery, so the different metals in the water will provide a electrical current between them. However, this current is very small so it's not going to eat a strong metal like a thru hull quickly."

and mine don't disagree - I was speaking on a macro level. I would agree with yours but on a micro level. For all practical purposes, the electrolysis induced by salt water on an isolated metal on a boat is negligible.

Regardless, this is too esoteric for us to debate.

 

[Bill Roosa]

Lightning storms not corroion guys

Since he is trying to make his boat safe (OK the people in the boat at least) the bonding question is really one that speaks to grounding the topside metal to the water in a way that the people (and hopefully the equipment) don't get fried!
The bonding network on a boat is not part of the lightning protection system. They are connected at the common ground as are the AC, DC, and RF grounds. With that said, I'd not tie every underwater metal thing together without some thought as to how it will survive a lightning strike. You could be setting yourself up for a hole blown in the boat or fried bearings on the engine/trany. I believe that is why the lightning grounding circuit is only tied into the other "grounds" at the common (read keel) grounding point.
General practice is:
#4 gage wire for the primary down path (masthead to keel)
#6 gage for the secondaries (shrouds, stays, etc)
never bend the wire more than 45 degrees
never put lighting protection wires in the same bundle with ANY other wires
avoid horizontal runs as much as possible (fore stay and back stay to keel)
The lightning rod should be at least 6" above all other stuff like radio antenna tips
There are two schools of thought in lightning protection. Ground the lightning to keep it away from people (the terrestrial model that works great when you don't run the line right through the middle of the room) and the unground boat mast and shrouds so the lightning "doesn't see them". Many have used lightning "dissipators". The folks that don't sell them say they can't work due to the amount of current you would have to pass to disperse a lightning strike while the guys that build the things say they work. Go figure. Statistically speaking you is less likely to be struck when ungrounded than when grounded. The lightning does get to do what it wants when you don't give it a path to ground so the risk is unground and get someone killed or ground and fry all your equipment. Prayer would seem to be an additional means of protection that could/should be called upon.

 

[dbdaniel]

Thanks everybody. I appreciate the help. Yeah my primary concern was not getting killed by lightning but the corrosion info was very helpful.