PS Advisor September 2007 Issue

Sistering Keel Bolts

A do-able project for patient, skilled DIYers.

I have a keel bolt issue with my 1981 Freedom 33. To bolt the keel to the hull, Freedom set stainless J bolts into the mold and then cast the keel around it. While I was trying to torque one of the six keel bolts (5/8-inch), it sheared off. The rest seem fine. As much as 100 foot-pounds of torque, and repeated hammer blows have not had any effect on them. However, I plan to install multiple sister bolts to be safe. Here is how: Drill bolt holes within a few inches of the old ones, then fill them with fresh water. Drill a small-diameter hole horizontally, from the outside, to intersect the bolt hole. When that "pilot hole" is in the right location, the water in the new bolt hole will run out of the pilot hole. Dig a rectangular pocket with the pilot hole in bottom center of the rectangle. (The pocket will be large enough to attach a backing plate and a nut to the bolt when it is inserted through the new bolt hole from above.) Wrap the space between bolt and nut, before tightening the bolt, with epoxy-soaked caulking. Torque the bolt, and fill the pocket with epoxy-soaked glass fiber.

Do you have any further advice?

Frank Minelli
Via e-mail

Fiberglass and lead are easy enough to drill, but drilling straight over a long distance can be a challenge.

Keep in mind that the Freedom 33 was initially a centerboarder, and TPI wisely decided a lead ballast keel made more sense. Before trying to sister keel bolts with the keel in place, check for delamination by tapping around the garboard and using a bent nail to pick at the sides of the hole left by the broken keel bolt. If all seems solid, inspect the broken bolt for corrosion—a potential indicator of what’s going on with the other bolts. The 5/8-inch size is small for centerline keel bolts, and using ¾-inch 316 SS or Aquamat 17 or 22 for sistering makes more sense.

Contact Pearson Composites for a copy of the ballast keel drawing. It will show which way the J-bolts face, and if there’s any other weldment buried in the lead.

Your approach to drilling and finding the new holes is appropriate. Determining how many bolts to sister is usually done by dropping the ballast keel and inspecting the existing keel bolts. Not doing that leaves you with only a torque test to determine the structural viability, and with the bolts over 20 years old, small in diameter, and one already failed, it would make sense to sister as many as possible. Pick the easiest to access to do first. When choosing tools: a 300-500 rpm heavy-duty, ½-inch drill is good; long ¼-inch, 3/8-inch, and ½-inch bits (18 to 24 inches) for the pilot holes, and extensions for these if necessary. (Note: The longer the distance from the chuck to the drill tip, the easier it is to go astray.) The final hole for the ¾-inch bolt can be done with a ½-inch drill bit extension welded to a ¾-inch bit, rather than mechanically fastened.

Make sure the window cut point is at about the same depth as the J of the original bolt. Carpenter chisels and drilling can be used to sculpt each pocket. Square stainless steel stock 3 inches wide and 3/16-inch thick can be drilled to make 3x3-inch-square backing plates for the nuts in each window. Use Marine Tex (epoxy filler) under the plate and forget the caulking. In the bilge, use the same SS stock to make backing plates but make them wider (3x5 inches), and place them athwartships, doubling them up (2) at each bolt. It’s important to fillet below backing plates with Marine Tex in order to provide a level surface, and prior to inserting the new keel bolt, coat the upper three-fourths with 3M 101 sealant. Tighten to bolt spec, and epoxy fill in the window cut. Check torque after a month of sailing.

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