Masterclass with Pip Hare

Metal fatigue and when to change your rigging

Crack initiation starts when the metal first gets put to work and is caused by the cyclical loading of metal components. In the case of standing rigging on a sailing boat, this is the loading and unloading of shrouds and stays. Think about the windward shrouds loading up, while the leeward side relaxes: this cyclical loading causes cell structures to develop within the metal, these cells gradually harden and then develop microscopic cracks.

The crack growth stage follows next and these microscopic cracks will develop into larger ones, which may eventually be visible to the naked eye on the surface of the metal component. The speed of the crack growth phase will alter depending on how often and how hard your rigging is put under load.

Ultimate failure is caused when a crack exceeds a size that results in the component no longer supporting load. Failure will be sudden.

Above: a small crack has developed in this stemhead fitting just above the forestay clevis pin. Left: wires can break, unseen, within swaged terminals