Imagine you take a paper clip and start bending it back and forth repeatedly. At first, it resists. But after a number of cycles, it snaps — even though you never applied enough force to break it in a single bend.

This is metal fatigue in action.

Applying the analogy to Yacht Keels -Keel bolts and hull structures experience similar cyclic loading — from waves, sailing forces, and even minor groundings. Each time the yacht heels or hits a wave, the keel flexes slightly, stressing the bolts and surrounding structure. Over time, microscopic cracks form in the metal or composite materials. These cracks grow with each cycle, until the component fails suddenly, just like the paper clip.

Why It Matters -The failure often occurs without warning, especially if inspections don’t catch early signs. Unlike a paper clip, the consequences are severe: loss of the keel, capsizing, and potential loss of life.

The focus on keel safety and inspection is centred around the keel bolts and how the keel is attached to the hull.

Metal / weld fatigue can cause keel failure external to the hull (as in the Big Hairy). This is the unseen part of keel failure and the hardest to detect.

Any checks keel safety checks mandated by World / Australian Sailing focus purely on the visual (with exception of the “wobble test” or tip test”). This has changed as of Dec 2025. Please read World Sailing OSR Special Regulations updated.

Tests do not target fatigue unless there are visible signs (cracks, movement). Visible and non-visible cracks can be a sign of fatigue and a danger to structural integrity. In this case it should be established whether it is dangerous via NDT Testing. (see Types of Tests)

Checklist – Keel Fatigue

Boats at Risk – Keel Fatigue
Boats with welded keels, that have done lots of sea miles, especially in harsh conditions are the most vulnerable. As discussed elsewhere in this resource the major issues likely to occur are around weld fatigue “More keels have been lost to weld fatigue than other causes”…. see Keel Incidents

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”” . See Further Reading. The link for the Technical Background will not work but just asking google for “Hasso Hoffmeister and keels” will bring up huge amounts of research conducted by this man.
Construction and ongoing survey by a qualified NDT organisation should be
undertaken, on a distance-sailed basis rather than a calendar basis, to
address fatigue. There is whole pages on the ISO related to welding standards. https://www.iso.org/sectors/engineering/welding

Further Reading

Checks to Stay Upright Australian Sailing 2024

Keels Are Falling Off Scuttlebutt 2018.

Keels: Out of Sight and Out of Mind My Sailing 2021.

Keel Fatigue – Technical Background Hasso Hoffmeister 2020.

Fatigue evaluation of Canting Keel Erland Nordin 2011

Ran Tan II Sail. Hayter. 2020.

So much knowledge exists on the Australian Institute of Non Destructive Testing (AINDT) website. Standards of education, qualification, and types of testing available.

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