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Corrosion and Rust Never Sleep

Staying ahead of them both on stainless steel and anodized aluminum requires diligence.

It’s been said that death and taxes are inevitable. I would add corrosion and rust to that list, at least for boats in salt water.

I do virtually all of my boating in the salt, and every great day ends with a good bath of the boat’s exterior to remove as much salt as I can. Even if I get back to the dock in the dark, I will rinse the boat religiously to remove the big pieces of salt, and then do a complete wash first thing the next day. I am a salt person at heart. That includes being committed to battling the corrosive nature of the brine.

Stainless steel is a blend of metals; underwater, it will stain less than other metals, but it is not always stain-free. Discoloration comes with exposure to salt, acid rain and dissimilar metals used for fastening. In severe cases, the discoloration can lead to rust down the hullside, or wherever the stainless is secured, particularly if the stainless steel is improperly bedded for shedding water.

I found an example aboard my friend’s Down East cruiser. At first glance, it appeared that traces of orange discoloration were bleeding out in a few sections from behind the boat’s stainless-steel bang strip, which was seated within the white vinyl rubrail. When we removed a length of the bang strip, several of the screws were rusting, one was missing and two were different sizes. We determined that the previous owner had made a quick repair. The chrome was chipped and worn off, and the white metal underneath was reacting to its exposure to salt water and air. That meant crust and rust.

We caught the corrosion in time, but barely. The questionable fasteners could have imploded, making a 15-minute job into one that required redrilling, refilling and an ample amount of sweat equity.

Instead, we cleaned the back of the bang strip, rubbed off the grime with fine bronze wool and metal polish, coated the backside with a thin layer of sealant caulk, and reinserted the bang strip with a dab of sealant caulk on the threads of new stainless-steel screws. More than a year later, we have yet to see any bleeding on the rubrail or hullside.

Stainless-steel bow and safety railing often develops spotting or staining due to salt exposure, minerals in washdown water or chemicals in precipitation. Some boaters do a sharp rinse with a hose, but that will likely drive salt into places that can’t be thoroughly rinsed. A quick pass with a sudsy mitt is another common option, but it cheats many areas.

My procedure for washing a stainless-steel railing has multiple parts. It begins with a water hose in one hand, spraying water on the railing, while my other hand rubs the surface back and forth. You can always feel the salt in your bare hands and know for sure it has been thoroughly removed. Pay special attention around the fittings and stanchions.

Once the railing is free of salt residue, I break out that soapy mitt and go over everything again with another generous rinse. The next all-important step is to wipe the railing dry with a chamois. This prevents spotting from any residue.

A metal polish from a brand such as Noxon or a felt-type applicator of metal polish will do a good job of removing discoloration and will protect the metal from further spotting. Just be careful when using metal polish around stanchion bases, which join the railing to the deck, toerail or other adjacent
areas. The chemicals in the polish and cleaning cloth can spread impurities, which will stain the gelcoat or painted surfaces where the stanchions are attached. Be sure to clear out any polish remaining in the screw head.

Anodized aluminum has similar care and feeding needs, but must be handled differently. The anodized coating looks great when it’s new, but the finish is easily scratched. Once moisture reaches the substrate, the condition can be further aggravated by salt spray or rain as it finds a home underneath the coating, which will likely continue to deteriorate. The coating is just a shield, and there is no reduction in the strength of the aluminum; however, the surface will start to accumulate white splotches or minor bumps, for which there is no true remedy.

Other areas where anodized aluminum requires watching is in welded joints, on flybridge and transom ladder rungs, on bow and stern railings, and where stainless-steel enclosure snaps or buttons are installed with aluminum enclosure tracks or snaps. The plight of dissimilar metals will quickly become apparent as a whitish coating or bubble develops where the stainless mates with the aluminum. In time, the stainless will win the corrosion battle, fusing the pieces together. This problem often makes separating the snaps or tracking nearly impossible without breaking something.

Savvy enclosure-makers often dab the screw threads with Tef-Gel, a corrosion-resistance compound that insulates and eliminates the seizing and galling potential of different
metal parts. Powder coating is an alternative to anodizing, with a wide choice of colors, but the gleam of anodized aluminum is equally attractive at a lower price.

Treating anodized aluminum also requires a little more attention than stainless steel because certain cleaners will injure the finish. Teak cleaners containing oxalic acid or similar chemical formulas will instantly turn silver anodized aluminum fittings chalky white, with no chance to restore the original sheen. I always make it a rule to neatly cover aluminum cockpit and bridge deck fittings with two layers of waterproof tape, to prevent any chance of the teak-cleaning supplies from wetting these fittings.

Be generous with soapy water and an abundant rinse when cleaning salt-covered aluminum, especially when your boat has an enclosure with a fabric top strapped to the aluminum framework. The cordage absorbs a lot of salt and dirt over time, and a clear rinse takes longer than you imagine. If your flybridge boat is outfitted with an enclosure, pay special attention to rinsing the enclosure from both sides, from top to bottom, to flush out as much salt and grime as possible.

Carefully wipe all of the aluminum with a chamois. Regular polishing and waxing are advisable to preserve the anodized coating. Not all metal cleaners or metal polishes are suitable for anodized aluminum surfaces, so read the labels to avoid unpleasant surprises. Generally, a polish compound will have some abrasive material in it to remove oxidation, stains and other impurities, but you do not want to injure the protective anodized layer.

If in doubt, opt for a fiberglass wax such as Collinite, Star brite or Woody Wax, and always try the product in a small area before going full tilt into the project.

This article was originally published in the May/June 2022 issue.