Mike Hatch, of Trinidad, West Indies, asks:
"My 36-year-old Pearson 390 has bronze through-hull fittings, which are starting to have a lot of surface corrosion. What’s the best way to keep them clean and bright?"
Don Casey replies:
Normally bronze seacocks and through-hulls turn green because the valves are weeping. If this is the case, you won’t be able to keep them bright unless you make them watertight. If your seacocks are original equipment, they are a tapered-plug design. The next time your boat is out of the water, you should dismantle each seacock and lap the plug into the body of the valve with valve-grinding paste until you get a perfect fit. Pack the seacock with waterproof grease when reassembling.
Unfortunately, the first time you turn the handle you may break the fleeting seal this grease provides. Tightening the nut might reseal the valve but is also likely to make it impossible to turn the valve without first loosening the nut with a wrench—not good in an emergency. Decades of surface corrosion can leave the exposed middle of a tapered plug wasp-waisted, making it impossible to lap the plug to a watertight seal.
However, if your servicing is successful and keeps the valves from weeping, an anticorrosion spray should protect them from any air-induced corrosion. I have had good results with Boeshield T-9 (www.boeshield.com), but I know others who swear by Corrosion X (www.corrosionx.com). WD-40 is not the right spray to use for this purpose. If you can’t make the valves watertight, you should replace them. I like Marelon composite ball valves because they are weep-free and are not susceptible to corrosion.