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Keel Cancer on a Cast Iron Keel “As the boat lifted from the water, we were immediately faced with one of the worst cases of corrosion and material loss to the keel that I have ever seen.”


ver the years, I have seen more keels than I want to think about. The keel is an extremely important part of your boat and contributes largely to the ballast, safety and handling of the vessel. There are numerous variations of keel design, all with specific intended purposes. At one end of the spectrum are the high aspect racing keels with extended bulbs and wing configurations that promote lift and decrease parasitic drag. On the other end of the spectrum are the full keels designed for oceangoing vessels that offer a much higher degree of stability. Most recreational sailboats have a modified keel that is much shorter in relation to the fore and aft component of the vessel. Today, the centerboard has fallen by the wayside to a new style of keel, which takes the modified keel design and adds a ballast bulb to the bottom of the keel allowing the keel reach to be shortened. These are termed as “shallow water draft keels.” These keels offer the sailor a good flexibility for coastal cruising, without too much of a performance loss from a traditional deeper keel. Recently, I had a customer who came in for bottom maintenance to his 30-footer. As the boat lifted from the water, we were immediately faced with one of the worst cases of corrosion and material loss to the keel that I have ever seen. As you can see from the picture, a large section on the starboard side was heavily pocked with material loss. The port side was not as bad. The aft-trailing edge of the keel where it connects to the foot was actually gone. My first inclination was some serious galvanic corrosion, but lead should hold up pretty well. Upon closer inspection, I discovered that the keel was actually made of cast iron. A cast iron keel required special attention when preparing the keel for paint. Without a good epoxy sealer to keep the saltwater from contacting the metal, it will quickly corrode and in this

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December 2010


case, exfoliation was present. The owner said the keel did not look like this two years ago when it was last hauled. Why would a boat manufacturer put on a cast iron keel instead of a lead keel? The simple answer is cost. A keel made out of lead for this boat would cost close to $30,000 dollars, while a cast iron one cost $10,000. As the market for boats continues to strain and price points increasingly drive the market, it is fair to say that boat manufacturers have to come up with ways to reduce cost while keeping the vessel design within the standards. Now for those of you who have a cast iron keel, don’t panic. All that is required is some vigilance and proper maintenance. Obviously, the previous paint job was not done correctly. Another important consideration was the condition of the keel bolts. If water penetrated the seam where the keel mates to the foot, there can be corrosion and subsequent failure of the keel bolts, which would be potentially catastrophic for the vessel. A torque check on the nuts was in order, and for this particular bolt size the book called for 100 foot/pounds of torque. Check with your manufacturer for the specific torque setting for your size bolt and nuts. If the nut breaks torque, then further investigation is required since the nut can loosen due to keel movement. Monitoring and checking the keel and nuts periodically goes a long way towards preventing this type of condition on cast iron keels. In order to effect this repair, I had to remove the loose material and clean off the rust. That entailed chiseling, wire wheel and blasting. Once the area was free of corrosion, I immediately applied an Ospho treatment ( to bind the exposed metal. Once the Ospho dries, the next step is to apply several coats of an underwater metal primer. Once cured, the cosmetic repairs can begin, using epoxy mixed with fairing fillers over several applications until the area where material loss occurred is filled. The trick here is mixing small amounts of epoxy allowing it to stiffen to the point where it will not sag as you apply it to the vertical surface. Your mixture should be the consistency of peanut butter, and as it tacks up, you can add subsequent thin coats until you achieve the desired level. Before the paste dries, you can take a file and shape the material, removing excessive buildup, which will