Cast lead or cast iron solid fin keels attached by threaded fastening studs (nuts/washers inside the bilge) or set screws (hexagonal bolt heads and washers visible inside the bilge, the latter usually with cast iron keels). These studs or screws must be pre-loaded by means of a torque-wrench to at least 50% of their tensile yield strength, such that they are always in tension and this load exceeds the normal service loads when the yacht heels or pitches. Due to embedding and settling, pre-load reduces over time and fasteners must be re-tightened to the original specified torque – consult the owner’s manual or a naval architect. As fasteners are made of various grades of stainless steel or non-ferrous alloys, there is a different torque needed depending on the material and thread lubrication, even for the same diameter. The “devil is (as always) in the detail”. Some fasteners have been found to have badly corroded so replacement is sometimes needed – this is easy for a set screw but very problematic for a cast-in stud – seek the advice of a naval architect. 

Hollow fabricated, often welded keel fins made from steel or aluminium. Welded keels are particularly prone to fatigue and very sensitive to design and fabrication detail. At its most basic level, it should be appreciated that sometimes, the fatigue life of a welded keel fin is less than the life of the yacht and must be repaired or replaced (on a case by case basis). Think of them more like a set of car tyres. The car lasts longer than the tyres. Welded keels should be designed, built and maintained in a specific way – they are not “set and forget”. More keels have been lost to weld fatigue than other causes. Construction and ongoing survey by a qualified organisation shall be undertaken, on a distance-sailed basis rather than a calendar basis, to address fatigue. 

High-strength cast, forged, machined and welded keels found on high-performance yachts are often deep draft and high-aspect ratio and must be designed by very experienced naval architects with a matching ongoing survey program. 

Timber keel fins, usually reinforced with composite face sheathing must be designed by very experienced naval architects with a matching ongoing survey program as they are prone to material property variability and moisture degradation. 

High-performance composite keel fins found on performance yachts are often deep draft and high-aspect ratio and must be designed by very experienced naval architects with a matching ongoing survey program. 

Lifting and canting keel fins found on performance yachts are often deep draft and high-aspect ratio and must be designed by very experienced naval architects with a matching ongoing survey program. 

Others… if the loss of the keel fin results in the majority of the ballast parting company with the yacht, whether it is designed and built like the above types or something else, it must be designed by very experienced naval architects with a matching ongoing survey program.