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
Practical Sailor has been independently testing and reporting on sailboats and sailing gear for more than 50 years. Supported entirely by subscribers, Practical Sailor accepts no advertising. 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