Classicyachtmag.com 12-13-07

A Grain of Truth is a column written by Karl Weinert for ClassicYachtMag.com
An on line magazine of superior quality.

Current is more than the direction of the water flowing ~
Are you Current on current? Part I

This article is about electrolysis on wooden boats. More often than not, wooden boat owners are unaware, that wooden boats are at risk as well as metal boats for deterioration from electrolysis. Please keep reading!

Recently, I spoke to several groups of people from a wide variety of professions; they seemed to be surprised electrolysis can have such a profound impact on everyday life. I thought this might be a very good time to include some information on electrolysis as it pertains to wooden boat bottom construction or replacement as well as tips to do and not to do. I am not an engineer, nor is this a lesson in metallurgy, but it is worth reading and becoming aware of how metals, water and electricity interact with each other – on wooden boats.

You might know if you’ve been following my articles, we are replacing the bottom of a 1960 cris craft, 24’. This information is particularly interesting and appropriate because the boat was just finished at another boat shop, and when the owner placed the boat in the water it began to take on water and started to sink in the boat slip. The boat was saved and delivered to the shop for investigation. Starting to remove multiple bottom planks there were multiple problems, poor re-fitting of the transom, large open gaps, bondo filler and stainless screws holding the planks onto the hull. The boat bottom was reassembled with stainless steel screws on a boat that had all brass fittings; this combination of mixing metals is a perfect scenario for accelerated deterioration of a boat bottom. Hull wood had deteriorated into mush. Upon removal the brass screws and bolts, crumbled or broke off as spongy pieces

CrisCraft originally built the boats with brass screws, not intending the boats for salt water use. Credit goes to the boat builders of yesteryear, after years of service the boats have held up pretty darn well. But today’s boat owners are in a unique situation: trailering the boats is easier than ever, which means you might use the boat in both salt and fresh waters. Perhaps you own multiple boats, new ones, older models on the cusp of needing a bottom repaired or replaced; or maybe you had a boat bottom redone and do not know which type of metal fittings the Boatwright used below the water line. As a boat owner you need to be aware of how dissimilar metals can be affected in fresh and salt waters, you need to be aware that other boats in the marina can affect your boat even when you’re just tied in a slip; but more importantly than those two critical things you need to be aware that shore power is the most destructive source of electrolysis.

Electrolysis is the process of two dissimilar metals in a solution bonded together that make electric current. Your wooden boat has metal fittings all over it, the boat lives in water [the solution] and water has minerals in it; these three things create electric current. This environment is similar to your car battery.

The car battery has metals and water [electrolyte] in it and together makes electric current. If you mix different metals on the boat hull below the water line; the less noble metals on your boat will be eaten away and disappear while in the water [solution]. Have you ever heard someone talking about a boat that sunk for no reason what-so-ever at the dock? The through hulls may have let go, no one knew to check the fittings or even knew to check for electrolysis; water started seeping in and before long the boat went down right for no apparent reason.

Before moving on, let’s address shore power for a moment. Shore power110 volt or 220 volts can eat all the metal in a boat below the water line, in a very short period of time – weeks in some cases. If there is a leak of voltage to the boat like a bad ground to the shore side wiring, the voltage will ground itself through the boats’ metal parts. A boat tied two or three slips from your boat [think marina or your own boat house, neighboring boat houses and docks] can destroy YOUR boat. The best protection for your boat is the use of sacrificial zincs.

It gets slightly technical here, follow these thoughts. You’ll understand this, just keep reading.

Brass is made of copper and zinc. Brass will rapidly de-zincify in saltwater, more slowly in fresh water. The copper is more noble than the zinc, causing the zinc to disappear, leaving the copper spongy and without strength. This means that the fastenings disintegrate and the bottom fails.

Bronze is made of copper and tin and is much more durable than brass. Stainless steel [SS] has iron, nickel and trace amounts of other elements in it. There are various grades of SS and dependent upon the grade, depends on how long they last. For example, 316 series SS is used in food grade equipment; it is strong and corrosion resistant. Often under water boat parts [i.e. shafts, struts, rudders] are manufactured with 316 SS. This can be used in salt water, but keep a watchful eye on it; because it can create its own closed cell corrosion which may lead to pin holes on the surface of the part that can keep growing larger, ultimately having the part weaken and fail.

Of note, even with sacrificial zinc, the 316 SS is not a miracle metal.

Sail boat rigging has problems with 316 SS.

304 SS is commonly used in hardware store bolts and will rust and fall apart in a short time, on a boat, especially in salt water DO NOT USE IT, AT ALL – EVER !

Where does this leave us and what do we use for boat bottom construction?

Use only bronze, silicon bronze or Everdur [a trade name]. Monel is another alloy, mostly nickel. It is about the best to use but very expensive hence not practical.

Nothing is better than an informed consumer. Educate yourself. Know what bronze fittings look like; know what 316 SS vs. 304 SS looks like. Have a couple of each in your pocket –label them if you need to - pull them out and compare to what will be installed on your boat. Question your boatwright about materials, if things sound iffy – ask to see supply lists, or the materials that will be used.

It’ll be you and the kids bailing out the water – probably not your boatwright.

Most professionals don’t taking some time to educate their customers. We don’t mind questions – in fact we prefer our customers ask some questions.

In conclusion, a quick article synopsis is: Personally, I have built, restored and owned many boats, all sizes; both motor and sail, and have never had any trouble with electrolysis because my prevention system really works.

Next column, I will discuss where to place your sacrificial zinc, to help prolong the deterioration of the through hull fittings and the fastenings on your boat(s).

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Keep your questions and feedback coming, we like hearing from you!
Best Regards
Karl Weinert, Master Boatwright
Karl Weinert Boat Works LLC [formerly Sandra Lynn Boat Works LLC]
Big Sandy, Tennessee
boatsbykarl@gmail.com
~ remember, anytime you return to the dock, it’s a good trip!