Hatteras 58 LRC Chain Stripper
Dear Steve: I am remounting a chain stripper on my anchor windless. I will be screwing a 3/8-16 stainless hex head screw in the aluminum main casting. Long ago, I replaced a SS sail track on an aluminum mast and used a yellow (?) liquid to separate the SS from the aluminum so it would not corrode. What is the best stuff to use now? Would Lock-tite work?
Many thanks,
Harry Whitehead
Harry:
Thanks for your note and query. Indeed, stainless steel and aluminum do have a habit of becoming inextricably linked when mated in the marine environment. The interaction is, however, considered a necessary evil and not necessarily prohibited as is the use of copper alloys such as bronze or brass with aluminum. The reaction that takes place between aluminum and stainless steel is galvanic in nature; the aluminum being less noble than stainless steel corrodes much like a zinc anode corrodes in order to protect a nobler propeller or shaft.
The second half of this equation, however, is the byproduct of yet another type of corrosion called poultice, aluminum oxide, the white powdery material that is often seen on aluminum that is actively corroding. Both are undesirable and the latter can cause stainless fasteners to become seized within aluminum threads. The good news is this phenomenon is easily avoidable. An essential component in the galvanic and poultice corrosion equation is moisture, if it can be excluded then neither will occur with much vigor. Here’s where your yellow paste, probably zinc chromate, comes in. Applied to the fastener’s threads it effectively excludes moisture (and air) and while other proprietary, and often expensive, products are available for this purpose, others will also work well, including LocTite (I’d use one of the lower strength varieties such as 242, which is blue) and ordinary polyurethane sealants such as those offered by Sika and 3M.
As long as what ever you use excludes moisture from the thread interface, and it’s compatible with the metal substrate, then the problem should not occur. I’ve successfully used this approach for years when installing hardware on aluminum masts. Beware, many anti-seize compounds contain graphite or copper, both of which would be galvanically incompatible with aluminum (graphite is among the most noble materials, so it tends to make any metal with which it makes contact corrode), while some silicone-based sealants utilize an acidic base, which can me harmful to aluminum.
Steve C. D’Antonio, Technical Editor