Tuesday, September 16, 2008

Galvanic Current in Wood Vessels

Had a couple of questions regarding galvanic current in wood which causes alloy wastage in metal fasteners and weakened wood structures... the attached pictures are of a Pacemaker which I recently surveyed where the builder installed a copper strap (on top of the keel) running aft from the machinery space. The problem is that in doing so...nearly 50 years later - the current flowing through this strap, the wood, keel bolts, underwater hardware et al - eventually damaged the wood keel which it was attached - thus producing fuzzy, cracked, and soft wood - sometimes covered with a fine white powder which is sodium hydroxide (usually next to a fastener or thru-hull fitting). The solution here....remove strap, clean - treat wood surfaces with distilled white vinegar (and maybe Restore-It), and monitor. The concern here is...if the damaged wood weakens the garboard seam there could be mass problemas - especially in this instance where the keel isn't particularly husky in the first place and is substantially reduced at the keel cut-a-way at the stern. The take-away wisdom here (at least in my humble opinion), is not to common bond underwater hardware in a wood boat.

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