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 whats going on with the other bolts. The 5/8-inch size is small for centerline keel bolts, and using -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 theres 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, -inch drill is good; long -inch, 3/8-inch, and -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 -inch bolt can be done with a -inch drill bit extension welded to a -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 3×3-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 (3×5 inches), and place them athwartships, doubling them up (2) at each bolt. Its 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.

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


  1. I developed this and other systems of keel bolt repair. What to talked about is called pocketing and works very well. The j bolts are usually down about 12″ below the surface of the lead. I broomfeild made the keel and should have a record of the keel bolts. The one thing that you have to worry about is don’t put the holes or “pockets at the same level. You will weaken the keel. Drilling lead is not easy to do so you need a lubricant to keep the drill from grabbing. Also put a strong magnet on a wooden dowel and super glue it to the dowel . put the magnet down the hole and get a pocket compass and find the magnet.
    I have heard about some so called experts saying sistering in keel bolts is not very good. Let me tell about my qualification I owned a keel making company called Keelco and made over twenty years 50,000 keels The biggest keel was 92000 lbs and we made 8 america’s cup keels and most of the racing keels for many of the US. After Keelco closed in 1990 I started doing keel bolt repair in 2000. I have repaired about a thousand keels with bad bolts. I also am a sailboat racer RET. I have experimented at Keelco with bolts holding strength with keel bolts cast into lead at various depths. Some one said that putting in keel bolts not in the same spot as the original keel bolt location would not have the same structural strength . If a keel bolt is next to a rib we put the new keel bolt on the other side of the rib. This keeps the structural strength in the hull. The bedding of the keel to the hull ,or keelson, can hold on a keel. I took of a 6000 lb keel of a Islander 36 one time and had to use wedges to pry of the keel after all the keel bolts and been cut of. when I wedged the keel of the hull I puled of the jell coat. That does not transmit the healing force into the hull, the bolts do. Like I said I have sistered over a thousand keels with out any failures. The boaters must retorque there nuts to the specs every now and then.
    DON’T PUT STAINLESS STEEL NUTS ON STEEL KEEL BOLTS. The stainless steel nut is more noble that steel and the nut will destroy the keel stud.
    Don Huseman 310 4186481 [email protected]