Zinc me before they sink me.

[John]

Scott,

Zincs.....and galvanic corrosion require both an electical connection and a conducting medium (salt water) to complete a circuit. Dissimilar metals along with the two previous items form a battery. The use of zincs is to provide a more active (less noble) side for the circuit so that the zinc is consummed rather than your boat part. Zinc is a very active metal, asi is aluminum.

This raises two points. The first is that in order to work, zincs need to be connected electrically (by wire) with the other metal items that sit in the salt water. If it doesn't sit in the water, it doesn't need to be bonded. And zincs not connected to the other items may corrode for other reasons but will not protect your boat.

The second point is more debatable, by some. There is a the thought that to bond (connect) your through hulls to the other metal in your boat is an invitation to disaster. If the zincs are consumed and the through-hulls are now the most active metal in the system, you now have a battery eating up the one thing between you anad the bottom of the harbor. There have also been some reports I have seen saying that galvanic corrosion can cause problems with the surrounding material, especially wood and soften and weaken them. I can't speak with any authority about that but I have heard it from some. So my recommendation is to bond everything but your through hulls.

There are two systems tying things together electrically in your boat. The first is the bonding system as mentioned above. The second is a grounding system tying all metal items above the water to the same electrical point, for lightning protection. Code requirements currently (sorry,,,I couln't resist) are for the main discharge path to be 4 ga copper wire or better and ohter paths to be no less than 6 ga or 20 ga copper strips. This may be the source for wire tying your shrouds and stantions together and might lead to a through hull (argghh).

If you have any questions, drop me an email...Also a shameless plug for the Power Squadron. Their Marine Electronics course (for members) is an excellent resourse for this and other information. Join a local squadron and avail yourself. (I am an ME instructor)

[Scott Galloway]

John,

So since conventional wisdom says to bond all metals except my thru-hulls, and since the only metal in my OB equipped (no inboard) Ariel is the rudder, and I have added zincs to the rudder shoe to protect the shoe and lower shaft and another zinc connected by a copper strip to the upper shaft, so that's it I suppose for bonding. I am stuill perplexed, however by Grocco's seacock installation instructions that say, "connect the sea cock to the vessel bonding system with 14 guage wire and a ring connector. A bonding screw bolt is provided on the sea cock flange for this purpose. Connection to the vessel bonding system must be in accordance with ABYC projects E-1, E-2, and E-9."

Although I do have some wires that must have led to what once was a linghtning grounding system, the wires now lead nowhere, unless of course somewhere there is a connection to my Loran RF ground (The rusted steel eye bolt in the bilge that is screwed into the lead ballast, which is encapsulated in glass, unless somehow the lead ballast is connected to the rudder shoe.

None of my former thru-hulls cockpit or head thru-hulls had attachment points. I have no other thru-hulls, so I better chase down those stray wires.

Can I rule out a connection betweeen by lead ballast and the rudder shoe, at least as built by Pearson?

[Toby]

I bought a used sail from someone in Minneapolis whose Commander was totaled after a lightning strike. His report is instructive...

As for lightning (the class of the first sailboat I owned), It was frightening to see pockmarks all about the hull at every place there was a wave peak when the bolt hit, while the boat was moored in 25' of water on the St. Croix. The areas with the chain plates were especially hard hit as the charge jumped from the plates, thru the glass at the waterline...I could put a key 3" into the delamination at the bow; amidships the scoop out of the hull was the size of a golf ball. The lateral damage from the travel of the bolt from amidship plates to the hull pass throughs and on to the motor mounts was frightening. It is a tribute to the old fashioned construction techniques of Pearson's glass lay-up that she didn't sink. I saw a cored Hunter in a yard hit by the same storm that received $15,000 worth of damage. There they were removing 1'x 2' pieces of glass - with that same golf ball sized scorch mark - that looked like the black aftermath of a grass fire on the resin impregnated interior layer.