Rust Converters

Can these solutions magically turn rust back to sound metal?

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Chances are good that anyone who owns or has worked on a vessel equipped with an iron keel has at one point or another come across products that, “turn rust back into sound metal,” or make other similar and often impossible-sounding claims. The question is: Do they work, and is this the best approach for an iron keel?

Iron Keel

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Make no mistake about it, iron is cheap, and thats the primary reason for its use where keels and centerboards are concerned. Lead is nearly always preferred, at least for ballast keels, because its denser and weighs more for a given volume than iron, and it doesn’t corrode. Some vessels use bronze as a centerboard material, and while its not as dense as iron, all sailors know it does not corrode. Irons use as a ballast keel or centerboard material comes at a price, a price that is paid over the life of the vessel by its owner or owners. If the iron is not properly isolated from the water in which the vessel floats, it rusts prodigiously. Some studies have shown that an inch of iron will create 16 inches of shale rust. The insidious nature of the way in which iron rusts is often its, or the vessel owners, undoing. Unlike steel, which tends to slough off as it rusts, iron often retains its shape, rusting from the inside out. Thus, it may look sound, however, a sharp blow from a hammer may release huge chunks of material. This type of decay is referred to as graphitization because graphite residue is all that remains.

So, can brush-on cures solve this problem? In our experience the answer is a qualified “No.” If the metal is a mass of shale thats falling to pieces, then no liquid is going to correct, halt, or reverse this problem. De-shaling, sandblasting, and then coating with a marine epoxy two-part primer is the only permanent method of arresting, but not reversing, this scenario.

Practical Sailors preference, by the way, is to stick with one manufacturer for metal preparation treatments, primers, top coatings, and antifoulants. Taking this approach ensures chemical compatibility of all components used in the process.

Some brush-on products weve used, however, do appear to arrest mild cases of rust on iron surfaces. One, Ospho (www.ospho.com), claims that it causes, “iron oxide (rust) to chemically change to iron phosphate-an inert, hard surface substrate that turns metal black.” Weve used this product. Provided no attempt is made to apply it over loose shale, it does stabilize the oxidation process, thereby halting the rust. It is designed as a primer of sorts; other coatings must be applied over it, the thicker the better, in order to isolate the iron from future contact with water. Look for a future Practical Sailor review of these products and their effectiveness.

Darrell Nicholson
Practical Sailor has been independently testing and reporting on sailboats and sailing gear for more than 50 years. Its independent tests are carried out by experienced sailors and marine industry professionals dedicated to providing objective evaluation and reporting about boats, gear, and the skills required to cross oceans. Practical Sailor is edited by Darrell Nicholson, a long-time liveaboard sailor and trans-Pacific cruiser who has been director of Belvoir Media Group's marine division since 2005. He holds a U.S. Coast Guard 100-ton Master license, has logged tens of thousands of miles in three oceans, and has skippered everything from pilot boats to day charter cats. His weekly blog Inside Practical Sailor offers an inside look at current research and gear tests at Practical Sailor, while his award-winning column,"Rhumb Lines," tracks boating trends and reflects upon the sailing life. He sails a Sparkman & Stephens-designed Yankee 30 out of St. Petersburg, Florida. You can reach him at darrellnicholson.com.