Story and photos by Troy A Buzalsky
I remember it like yesterday, even though it was 40 years ago. Sitting in Fire Science on day one, the instructor Cecil Dill, a salty ole dawg whose face was carved deep not with wrinkles, but with wisdom, asked the group of firefighter students to define fire. Sitting front and center was an older first-year student named Steve Able, who hailed from Ketchikan. Steve’s hand went up and he fired off, “Fire is defined as rapid oxidation of a chemical producing heat, light, and smoke.” Cecil grimaced, affirming the answer. Of course, we were all in awe that Steve had the answer, but more importantly, his answer made me think deeper about the meaning. In my mind oxidation was more closely aligned to the process of ferrous metal flash-rusting or aluminum dulling with an oxide film…certainly not fire.
There’s no doubt that fire is a destructive process, whether used as a tool or when accidental and out of control. Fire can rapidly oxidize your firewood to a pile of ashes, or can cause unthinkable destruction. Rust is a very slow process and generates minimal heat or off-gassing, whereas fire is a very fast process generating massive amounts of heat and gaseous byproducts. In reality, both are forms of oxidation.
In the aluminum-boat industry, there are three types of oxidation that can wreak mayhem on your aluminum hull: galvanic corrosion, electrolysis, and crevice corrosion. Often confused with each other, echo these words in a crowded room of boating enthusiasts and you’ll get an earful…Not necessarily accurate input, but still an earful, as these words are an ever-present threat to the aluminum-boat owner. These processes of oxidation can also be controlled and largely prevented with proper understanding and safeguards.
By definition, oxidation is the loss of electrons during a reaction by a molecule, atom or ion. Like with aluminum, as the oxide layer grows the rate of electron transfer decreases offering a protective layer. That being said, the oxidation process may continue if the electrons succeed in entering the alloy through cracks or impurities and this is where and when damage occurs. Just as rust will create red/brown flaking when hyper-oxidized, aluminum will pit, flake, and spall when the oxidation is aggressive and unchecked. All too often, susceptible areas are out of sight and out of mind.
Aluminum and metal boats and surfaces are subject to corrosion which can increase when a boat is moored. Saltwater and marine environments pose a more extreme risk of galvanic corrosion, electrolysis and crevice corrosion; however, any impure water can serve as an electrolyte which sets the stage for these processes. Simply put, galvanic corrosion is caused when two dissimilar metals come into contact with each other while immersed in an electrolyte. Electrolysis is the result of potential current (AC or DC) existing between two different objects, usually caused by stray electrical current that travels through the water (electrolyte). Crevice corrosion is caused when moisture (electrolyte) is trapped in a crack or crevice, or any other space that can trap and stagnate moisture.
If you are the proud owner of an aluminum boat, whether you use it for fishing, cruising, watersports or transport, your aluminum boat is built tough and made to withstand most of the hazards of boating. However, having a better understanding of these corrosive problems can add years of pleasure to your boating lifestyle.
When mooring your boat, you are only as safe as your neighbor and the boat harbor. The more you know about electrolysis, the better you can safeguard your boat from future damage.
When we think of quality construction it’s easy to be enamored with high-quality stainless-steel and brass componentry, however, that stainless-steel through-hull fitting might not be the best decision on your aluminum hull. I’m not saying you can’t use a stainless through-hull fitting, cleats, or rod holders, but special precautions must be used to reduce the potential for galvanic corrosion…which can be thought of as dissimilar-metal corrosion.
Galvanic corrosion occurs when two dissimilar metals are brought together in an electrolyte solution, which might include your local lake, the brackish water in your local estuary moorage, or when enjoying the big blue.
Stainless screws and fittings that were not isolated allowed galvanic corrosion to take hold.
Interestingly, galvanic corrosion was discovered in the 18th century by Luigi Galvani, hence the name. When the two dissimilar metals are joined, like when a stainless-steel bolt is fitted into an aluminum stringer, the connection is called a bimetallic couple. A galvanic couple occurs when one of the metals becomes an anode and the other a cathode. The anode (the less-noble metal) corrodes faster and the cathode slower than they would if not coupled, creating a galvanic response.
Care was used when reinstalling to isolate the stainless fitting from direct contact with the aluminum hull.
The galvanic relationship between metals must be understood when joining two different alloys to create the lowest tendency to interact galvanically. Scientifically speaking, from the anionic scale, with zero being the most cathodic, gold scores 0.00; brass -0.40; iron -0.85; aluminum -0.90; zinc -1.25; and magnesium -1.75. When galvanically coupled, the metal with the lower number (think in negative terms) will corrode preferentially faster. This differentiation will also indicate the need or degree of protection to be applied to lessen the expected potential interactions.
The nuts and bolts of galvanic corrosion quite literally affect the nuts and bolts used during the boat-building and accessory-fitting phases when decking out that boat of a lifetime. Boat builder and boat-repair specialist Mark Oldenstadt of Motion Marine was an early pioneer of galvanically isolating fasteners to reduce the galvanic reaction. Much of Motion Marine’s early service work included damage caused by dissimilar metals. The typical culprit was a stainless-steel screw, bolt, or rivet placed into the aluminum structure of the hull. In this case, the stainless steel became the cathode, and the aluminum the anode, and in short order a galvanic reaction occurred, including pitting, flaking, paint blistering, and spalling of the aluminum structure. In some cases, leaks or even more catastrophic damage occurred. Understanding the lessons from Luigi Galvani, Oldenstadt painstakingly isolates each and every dissimilar metal fastener and contact point on the boats they build and repair, and sometimes that’s easier said than done.
Boat-top snaps are made from plated steel, and thus can create a galvanic reaction. Using nylon isolators helps curb corrosion.
The ABCs for cathodic protection can be easily found in the American Boat and Yacht Council (ABYC) Standard E-2 governing the appropriate levels of cathodic protection for various hull configurations and materials. This is a technical document that dives deep into electrical science. ABYC recommends that a cathodic-protection system shall be capable of inducing and maintaining a minimum negative shift of 200 mV relative to the corrosion potential of the least-noble metal being protected. To simplify the jargon, ABYC recommends hulls be protected with sacrificial anodes, and when practical, underwater fittings that are more noble than aluminum be isolated from metallic contact with the hull. Zinc is the recommended anode for aluminum-hull boats being used in saltwater applications and magnesium may be used in freshwater applications. Aluminum anodes are becoming more popular as they protect in both saltwater and freshwater environments.
Electrolysis and Stray Current – Hot Boat and Moorages
I remember vividly sitting in a hog line on anchor with at least a dozen of my closest friends…In fact, they were so close the boats were literally boat bumper to boat bumper. The bite was steady until a new angler joined the fray. Our bite suddenly died, but interestingly, other hog lines upstream and downstream were still producing steady hook-ups. Within our network of anglers, someone shouted, “Who let the “hot boat” in our line?” This wasn’t a reference to a nice-looking boat; it was a reference that the boat may have been electrically hot, sending off an unpleasant voltage signal to the migrating salmon under our boats. This hot-boat phenomenon is what’s known as stray-current corrosion, caused by a boat’s wiring system, and misunderstood as electrolysis.
A painter from Austin’s Auto Body lays down new paint on a boat that was repaired for both galvanic and crevice corrosion.
The term “electrolysis” is actually a very specific condition, but boaters often use it interchangeably with several other terms. Clinically defined, electrolysis is the forced introduction of an electrical current in an electrolyte (water) to separate the components. In water this produces hydrogen and oxygen, and the process is opposite to galvanic corrosion.
Electrolysis is an invisible electrical AC or DC force that will literally chew away at a boat’s structure and componentry, and often occurs at moorage. This translation basically means your boat is only as good as your boat’s wiring, your neighboring vessels’ electrical systems, and the marina’s electrical services. Although it’s generally not enough stray current to cause a life-safety concern, it’s certainly enough to start the process of electrolysis corrosion.
The best protection from a boat’s stray current is a well-maintained bonding system that meets ABYC standards. Unfortunately, these systems tend to get overlooked when it comes to maintenance and haphazard accessory installations. The purpose of bonding (different than grounding) is to equalize the electric potential of dissimilar underwater metals by tying them all together with wire. The benefits of a bonding system are to dissipate stray current leaks. Twelve volts of current focused on a small piece of metal will result in rapid destruction, whereas the same 12 volts spread over a much larger surface causes less damage in proportion to the size of the water-exposed surface of metal.
To safeguard your boat against electrolysis and other corrosive effects Captain Obvious might suggest lessening your time soaking in the moorage bay by either using your vessel (fishing would be my choice), or removing the boat, cleaning and dry-docking it until your next outing.
For moored vessels, a galvanic isolator is a device installed in series with the AC grounding conductor of the shore power cable to block low-voltage DC galvanic current flow but permit the passage of alternating current (AC) normally associated with the AC grounding conductor. This device helps combat corrosion caused by electrolysis and stray current found in moorages.
Zinc anodes are an important protective element that not only need to be installed on the boat’s hull, but also on any accessories subject to galvanic corrosion or electrolysis.
As mentioned with galvanic corrosion, the proper type and number of anodes is your boat’s first defense against electrolysis. Bottom paint is another protective measure; however, when electrolysis is running rampant it can cause a failure to this protective layer. To play it safe, the ABYC recommends that “aluminum vessels shall have a protective paint coating that provides a high [electrical] resistance barrier between the aluminum and the water.” As a footnote, copper-based bottom paints can react severely with stray electrical currents and should be considered carefully.
I recently sold a boat that I owned for over a decade. During my ownership I pridefully maintained it as a valued part of my family. It was a heavy-gauge aluminum jet boat that I used in the Pacific Ocean, up the mighty Snake River, and everywhere in between. After a few short years of ownership and after the warranty had expired, the boat started to get corrosive bubbles forming under the paint, primarily at the paint’s edge. Left unchecked, this corrosion spread like acne on a teenager. The culprit in this case was crevice corrosion.
Crevice corrosion gets its start when contaminated water is trapped against the aluminum, which is what occurs under paint edges that were not properly prepped.
Crevice corrosion as defined by ABYC is the corrosion of an active-passive metal caused by a breakdown of the passive film, which is initiated by a low oxygen concentration due to localized depletion of oxygen in restricted bodies of electrolyte. What this actually means is any trapped and contaminated water sets the stage as a breeding ground for crevice corrosion.
My buddy, Vinnie (I know it sounds like a movie title), recently pulled the floorboards from his 1999 vintage aluminum boat that was in showroom condition. The floatation foam was very wet in a few areas, and in one particular spot the aluminum hull was tinfoil thin, triggering significant repairs. The trapped water, in an oxygen-deficient environment, proved catastrophic; but repairable.
Vinnie’s boat had extensive pitting from trapped water in the floatation foam. This would be considered crevice corrosion, and the aluminum in question had to be cut out and replaced, which is no easy task.
To reduce the potential for crevice corrosion, aluminum boats used for saltwater fishing and cruising should not be manufactured with crevices or joints that might collect water and trap water. The design should also promote moisture, including condensation, to drain away with no sealed or dead-air spaces. Top-paint systems need to be approved for aluminum use and both paint and vinyl-wrap applications need to reduce sharp edges that allow water to penetrate.
My grandmother always said, “Cleanliness is next to godliness,” and that could not be more accurate to reduce the potential for crevice corrosion. Products like Salt-Away, which I’ve used countless times, or other products like CRC Salt Terminator, Starbrite Salt Off, Un-Duz-It, or the foam-cannon Salt Wash system from Salty Captain are worth consideration.
When it comes to protecting your boat from the assaults of corrosion, the old saying, “An ounce of prevention is worth a pound of cure” couldn’t be truer. Do your part staying ahead of the corrosion curse and you’ll be paid off handsomely for your efforts.
Troy Buzalsky is the Boats columnist for Fish Alaska magazine, and when not writing about boats he can likely be found chasing fish in the Pacific Northwest and the 49th state and writing about those adventures. Troy can be reached at firstname.lastname@example.org.