Keel and keel bolts

The keel supplies ballast and lateral resistance. A bolted keel is a lead or cast-iron external casting clamped to the hull by keel bolts or studs through an internal reinforced sump. The visible seam between keel and hull is the keel joint. An encapsulated keel places ballast inside the hull laminate and has no external keel-to-hull bolts, although its surrounding laminate can still be damaged. Some designs use an integral fin structure with internal ballast.

A keel smile is an opening or crack at the keel-hull seam, often most visible at the forward or aft end. It can be superficial fairing/sealant movement, loose fastening, hull/keel deformation or evidence of grounding. The internal floors and sump around the bolts are as important as the external seam. Keel bolts may be exposed heads, nuts on studs, or partly hidden beneath tanks/liners.

The keel carries enormous cyclic and grounding loads. A compromised keel attachment can leak, crack floors, distort the hull or, in the extreme, lose ballast and capsize the boat. Less dramatic defects still consume expensive yard time because proper diagnosis may require haul-out, interior access, bolt testing or dropping the keel. A cosmetic seam repair that hides movement is worse than an honest visible seam.

Service includes removing loose fairing/rust, treating an iron keel, renewing compatible seam sealant and fairing/coating. A superficial smile can be opened, inspected and repaired; merely painting over it proves nothing. Accessible nuts may be cleaned and protected. Retorquing is done only with builder/engineer specifications—randomly tightening old fasteners can damage laminate or studs.

Diagnosis can include dye penetrant on exposed stainless, ultrasonic testing of suitable bolts, torque observations, core samples or dropping the keel. Replacing one accessible stud may be possible; other designs require lowering the entire casting. Structural floor/sump repairs need an engineered laminate schedule before keel reinstallation and alignment.

• Covered by a standard survey — external seam/smile, impact scars, keel corrosion, accessible nuts/bolts, bilge weeping, sump/floor cracks and sounding/moisture around the attachment. The haul-out is separate logistics but the observation is core survey scope.
• Not covered — bolt removal, ultrasonic/dye testing beyond simple surface review, torque certification, keel lowering or engineering of cracked floors. A specialist costs roughly $1,000–$3,000 before yard work. Do it before purchase when there is material bolt corrosion, active leakage, a fresh unexplained seam repair, significant grounding or structural cracks.

• The broker or owner — “Send all grounding, haul-out, keel-joint, keel-bolt, sump and floor repair invoices and before/during/after photos.” “State keel type and casting material from builder records.” “Have bolts ever been retorqued, tested or replaced, and under whose specification?”
• The surveyor — “Inspect the seam immediately at haul-out before washing if possible; map cracks and rust/weeping; examine every accessible fastener and the entire sump/floor load path; and distinguish fairing movement from evidence that requires specialist testing.”

Before the bottom is pressure-washed, look for rust or water tracks from the joint. Sight from bow and stern for a keel that appears skewed. Photograph every crack with a scale. Inside, dry the sump and return later for weeping. Look for dished washers, orange trails, cracked gelcoat radiating from floors, detached tabbing and fresh paint or sealant only around bolts. Ask where the inaccessible bolts are; “none there” may simply mean hidden by a tank.