Keel Bolt Anxiety
Doug Nicholson of Seattle, Washington, asks:
“My 5-year-old, 37-foot sailboat has mild steel keel bolts, nuts, washers and channel spacers securing a cast iron keel. The bolts, nuts, etc. are all quite rusted. The shallow bilge has not been kept dry, and they’ve been sitting in water for some time. How worried should I be? My surveyor suggested I just “knock off all the rust and keep them painted.” Should I plan to replace the keel bolts with stainless ones in the next few years? The iron keel is also weeping rust.
My plan is to grind the rusty spots back to clean metal and repaint with primer and bottom paint. Or should I seal the keel with epoxy first?”
Don Casey replies:
Keel bolts are a legitimate concern as boats age, particularly because they are difficult to evaluate. But keel bolts on a 5-year-old boat should not be at high risk. Your surveyor is probably right; clean them up and keep them painted and as dry as possible. Catastrophic keel failure is extremely rare, except on extreme racing boats. If you are really worried, pulling a bolt or two for evaluation might put your mind at ease. Putting in stainless steel bolts, by the way, is not a panacea. In the oxygen starved environment where most keel bolts live, stainless steel will also be susceptible to corrosion.
Touching up the rusty spots on your iron keel with some primer is a reasonable short term plan if they are few in number. In general, however, owner-applied primers don’t last long on iron keels. The best long-term solution is to clean the metal bright, then immediately coat it with epoxy, wire brushing the metal through the wet epoxy. This removes the flash rust and creates the best bond between the metal and epoxy. This initial coat should be followed by several additional coats of epoxy. As long as the epoxy is around 20 mils thick and remains intact, the coated keel should not rust.