When and how often should I check the rig?
Reliability experts often use the "bathtub curve" to explain how products behave over time. The curve does not represent how a single item behaves, but rather an entire population of the same item. In this discussion, it refers to the rigging on all yachts, not the rigging on a single yacht.
The bathtub curve consists of three distinct areas: the initial phase, known as the "Infant Mortality" phase, which is relatively short and is characterised by a decreasing failure rate over time. The failures associated with this phase are always caused by material defects, poor design or assembly errors. The middle phase known as the "Useful Life" phase, is characterised by a low constant failure rate and is caused by random failures. And the final phase, known as the "Ware-Out" phase, is characterised by an increasing failure rate over time and is simply a fact of life - all things have a finite life expectancy.
The curve is a graphical representation of how products behave in general, there is simply insufficient data to construct a precise graph to predict how many rigs will fail after a certain period of time. If it were possible to collect sufficient data one might be able to see trends. For example, a rigging company takes on a new employee and suddenly the infant mortality failure rate increases, possibly due to insufficient training; another example might show that the infant mortality has increased across a number of different riggers, possibly due to a poor batch of components sourced from the same supplier.
In some industries, it is possible to significantly reduce the infant mortality rate using a process called "burning in". This is where each product is operated or used sometimes at extreme conditions in order to "tease out" any potential defects. This kind of testing is often prohibitively expensive, only being used in life threatening industries such as the military.
Given the above, it is easy to see why a skipper planning a long blue water cruise should not replace the rig immediately prior to the trip. If it is to be replaced, far better to do it the season prior to departure - or better still have it tested as well. If it is unavoidable to change the rig immediately prior to departure, then testing is the only sure way to reduce the risk of an infant mortality failure.
Notwithstanding, at the very least, you should visually inspect your rig annually, our recommendation is to test the rig when it is new and again after a relatively short period - six to twelve months. This should filter out the majority of potential infant mortality failures. Thereafter regular testing once every three years will screen against some random failures and generate a history of readings which will indicate the onset of the ware-out phase.
Photo Courtesy of: www.yandina.com