Galvanic Corrosion is a silent killer of your wallet. It starts off so quietly and slow, barely noticed until it develops into a very expensive problem that will cripple your aluminum mast!
This mast has been pulled for winter storage of the yacht. The spreaders are neatly stowed inside the hollow spar for safe keeping. The bottom of the mast where it rests over the mast step is bubbling up with galvanic corrosion and this means that the mast is slowly but surely dying right at the base!
In a situation like this, the mast base will eventually become too weak to support the loads it is subjected to while sailing. The mast will ideally crumble down onto the mast step and all the rigging will go slack as the mast instantly becomes a few inches shorter. We all know that nothing on a sailboat breaks ideally, and instead the good aluminum just above the step and bad aluminum will slip off to the side of the step and the whole mast will come toppling down in a horrific and catastrophic failure of the rig!
For comparison, this is a perfect mast with absolutely no problems occurring at the step! Now, why is this happening to the first mast and not to this mast? Well, to put it simply, it’s because this mast is fully protected by paint and other insulating layers. There is no contact between the aluminum of the spar and any other metals, hence no cause for galvanic corrosion. The mast above must have a tiny scrape in the paint or contamination with a different metal around the mast step because the damage is localized only to the step of the mast and no further.
The damaged mast doesn’t need to be replaced, the solution is actually quite simple. The affected portion of the spar should be stripped bare and evaluated. If the corrosion is too extreme, the section is simply cut off and the mast made shorter. If the corrosion is minimal, a new coating of paint is in order to isolate the metal and protect it from further and future corrosion. Lanolin can also be used around the mast step to act as an insulator and protect against galvanic corrosion where the mast meets the step.
This mast, however is suffering from much more crippling damage.
You can see the paint bubbling up around the screw holes. This is caused by galvanic corrosion between the stainless steel screws and the aluminum spar. Apparently, no isolator was used, and if one was used, it has failed as isolating the two dissimilar metals leading to galvanic corrosion of the aluminum. The problem with this is the location.
Unlike with the other mast where the damage was located at the bottom of the spar, this corrosion is occurring on the side of the mast. If left unchecked, the side will form a hole and severely weaken the mast. This area is also in one of the highest stressed areas of the spar: The head.
All the forces of the sails, halyards, and rigging culminate at the head of the mast in the area of the truck (where all the welds are) and this is exactly where those little screws are bubbling away the aluminum of the spar. Eventually, the mast will break and make a big mess of the boat below it!
The corrosion still looks minimal and the screws do not appear overly critical. They could easily be removed and the area cleaned and protected. If they are necessary, then they can be coated in lanolin and reinstalled, paying close attention to the area in future rig inspections for any sign of renewed corrosion in the area.
If these small bubbling corrosion points are left unchecked, they can lead to very dramatic and costly results. Be sure to check any fasteners in the mast with a close eye and hold the area to the utmost standards of perfection. When it comes to your spar, there is no “good enough”!
