Spar Corrosion Demystified - SailNet Community

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Old 07-01-2002
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Spar Corrosion Demystified

Is there a way to tell how bad the corrosion is on an aluminum mast?

Mark Matthews responds:
Aluminum spars usually donít require a lot of maintenance. About the best thing you can do for them is to hose them off with freshwater on a regular basis, and apply wax when the spar is unstepped for its regular inspection.

If you're looking for corrosion, you'll likely find it where dissimilar metals meet. Stainless-steel fasteners that sit in contact with aluminum will cause corrosion overtime, especially in saltwater environments.

Unfortunately, a thorough inspection is not something that can be done in a bosunís chairóthe mast needs to come down and receive a closer look than is possible while you're swinging around above the boat. Youíll want to focus on areas of high stressóthe masthead, the spreader attachment points, the shroud and stay attachments, the sheave boxes, and the mast step in particular, and of course youíll want to make sure the mast is straight as well.

Aluminum and stainless if not properly isolated can all but weld together after enough time in a marine environment, so care needs to be taken. You should back out all the fasteners. And any bumps, deformities, cracks, or other anomalies in the spar should be addressed at this time as well, with an especially critical eye devoted to high-load areas. The best bet is to remove all fasteners using an impact wrench if necessary, and then reattach the fittings with new fasteners, taking care to insulate dissimilar metals, using silicone, electrical tape, or nylon washers.

Also, anywhere water can enter and anywhere water can pool should be regarded as a potential areas for corrosion. If the aluminum is crumbling, and flaking out, which usually occurs at the maststep or under the winches, youíll know see this pretty clearly.

There are also a number of dye kits that can help illustrate the severity of corrosion youíre dealing with. If you have any doubt about the sparís integrity, consult with a professional rigger. Inspect all the mast fittings extremely carefully. Any sign of wear or distortion should qualify that part for replacement. For more information, have a look at the following articles here on the SailNet website:

"Standing Rigging Storage" by Jerry Hammil

"Standing Rigging Basics" by Mark Matthews

"Avoiding and Surviving Rig Failures" by John Kretchmer

"Upgrading Spars" by Tom Wood

Should you like a quote on a new rig or more advice, feel free to contact SailNetís Custom Rigging Shop.

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