Sailboat KnowledgeBase

Keel Bolt Repair

Fred Anderson
My newly acquired 1992 Hunter 33.5 had not had her keel torques in her recorded history. I took it upon myself to do this deed. She has 1 x 3/8" and 7 x 3/4"-10 SS studs with large flat washer and a nut against the bilge floor. Hunter wrote to me with the required torque value of 132 foot pounds. 6 of the 7 bolts tightened up fine, the last bolt sheared off at the floor of the bilge. This was the forward most bolt. This bolt `was being used as the bonding stud for the ships ground tie plate. The reason for the failure is important and worth the few extra line required.
The bonding plate was bolted to the floor of the forward bilge compartment directly aft of the transducer compartment. This compartment does not drain directly into any other compartment, so any moisture or water that lands there will stay until it evaporates or gets cleaned out. This will cause the ground plate to develop corrosion and resistance to ground stud. The resistance will increase over time and eventually cause electrolytic corrosion to occur at that junction and rot away at the stud. The problem was further compounded by the fact the keels protective paint was no longer effective in insulating the steel keel from the water.
I researched the fix for the broken stud and got 2 solutions:
1. Drop the keel and replace the stud.
2. Drill a new 3/4" hole near the broken part and tap for 3/4"-10 treads. Then install a new bolt.
Neither of these solutions was attractive to me, so I used a SS 3/4"-10 threaded insert with 1 1/8"-12 external threads. The reaming stud was ground down to good material and the threads dressed so the insert would engage. A circle diameter of 1 1/4" was bored into the floor of the bilge to a depth of 1/2" around the broken stud. This allowed clearance for the insert. The insert was screwed to the stud, a large pattern washer and nut were applied and the void was filled with 5200. The new nut was torqued to the 132 foot pounds. The cost of the parts was under $40 to include new hardware to relocate the bonding plate to the top of an adjacent keel bolt.

Upload file (pdf, NOT photos)