Bilge Oil and Keel Worries

Stains at keel joint indicate need to re-bed keel bolts.


I have been looking at purchasing a Catalina 36 that had an engine oil leak, but first I wanted your opinion. The leaked oil accumulated in the bilge, and, in time, appears to have percolated through the base of the hull on either side of the keel, through the holes in which were mounted the sum/log impeller and the depth transducer. On the underside of the hull, there is a 4-inch dark halo that has impregnated the antifouling around each of these two fittings. I am concerned that the oil will damage the components and bedding seals. Also, the percolating oil has seeped down the keel bolts and darkened the joint where the ballast-keel meets the keel stub.

Nathaniel Montague

Relative Wind, Catalina 27

The oil around the transducers will be relatively easy to fix (more on this later). The toughest trick will be sealing the bond-line at the keel, which will be very difficult to carry out so long as oil is present. In a worst-case scenario, you would have to pull the keel and re-bed it as described in our January 2008 PS Advisor.

The existence of a “smile” at the keel joint suggests that the keel bolts need to be re-torqued to the manufacturer’s specifications (probably around 105 foot-pounds). In addition, this gap is frequently an indicator that the joint between the hull and the keel is not fair. This allows the keel to move under load, with enough force to break the bond on even the most tenacious sealant. If you find yourself resealing the keel-joint every season, you likely have one or both of these issues: lightly torqued keel bolts and an uneven interface between the ballast and the keel.

If this is the problem, then you will almost surely have to go through the re-bedding procedure. Unfortunately, you will not know for sure whether this is a problem without dropping the keel and inspecting the mating surfaces. Once you have dropped the keel, ensuring a good fit is a relatively straightforward process. The January 2008 article described how to mold a new mating surface using a sheet of heavy polyethylene plastic and a high-density Chockfast (

As pointed out in this month’s article on how to conduct a do-it-yourself, pre-purchase survey, it is best to assume the worst and budget for it. However, it could be that the oil has merely seeped through tiny crevices in the keel bolts, and these crevices might be sealed without dropping the keel. The challenge will be flushing out the oil.

Surveyor Jonathan Klopman ( in Marblehead, Mass., offered this possible solution for flushing the keel bolt holes and joint so they may be safely sealed:

“Pull the nut and washers on the keel bolt, then remove all traces of caulking compound around the threads. Scrub the surrounding fiberglass with degreaser and dry. The only way to get solvent down into the joint is with pressure.

“You can try a temporary fixture by securing a section of PVC pipe to the hull around the keel bolt. If the length of pipe is tall enough, then the pressure head of the fluid will force it down into the joint. Failing this, you can fill the pipe, cap it, and then fit a Schraeder valve to the cap.

“Very judicious use of the bicycle pump to your homemade pressure vessel should create enough force to drive the solvent through the joint. It would be prudent to use a pump that includes a pressure gauge—I would use no more than 3 to 5 psi. I would imagine that repeated flushing of the joint in this manner should serve to degrease and clean the surfaces.

“Once you are suitably proud of yourself, button everything up with fresh sealant. In this case, I would recommend a semipermanent adhesive/caulk such as 3M 5200.”

Catalina pointed out that having the transducers in the bilge sump was not a factory installation, and suggested relocating them. Catalina typically installs its transducers forward of the keel and that was where the company recommended installing depth or tri-data transducer, if you wanted one. Klopman also suggested pulling the transducers and fiberglassing in the holes.

Darrell Nicholson, editor of Practical Sailor, grew up boating on Miami’s Biscayne Bay on everything from prams to Morgan ketches. Two years out of Emory University, after a brief stint as a sportswriter, he set out from Miami aboard a 60-year-old wooden William Atkin ketch named Tosca. For 10 years, he and writer-photographer Theresa Gibbons explored the Caribbean, crossed the Pacific, and cruised Southeast Asia aboard Tosca, working along the way as journalists and documenting their adventures for various travel and sailing publications, including Cruising World, Sail, Sailing, Cruising Helmsman, and Sailing World. Upon his return to land life, Darrell became the associate editor, then senior editor at Cruising World magazine, where he worked for five years. Before taking on the editor’s position at Practical Sailor, Darrell was the editor of Offshore magazine, a boating-lifestyle magazine serving the New England area. Darrell has won multiple awards from Boating Writer’s International, including the Monk Farnham award for editorial excellence. He holds a U.S. Coast Guard 100-ton Master license and has worked as a harbor pilot and skippered a variety of commercial charter boats.


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