I’ve been told I must replace my rigging every ten years. Is there any proof of this?
It is often quoted that standing rigging should be replaced after ten years. There is no statistical or scientific logic that supports this ten year theory. Widespread application of stainless steel rigging started in the 1940’s and 50’s but nobody really knew much about the lifespan of this wonderous material. The old galvanised steel wire was a known quantity. The wire was wound around a rope core which was saturated with oil. Individual stays and shrouds would be taken down and soaked coiled up in barrels on Ensis Oil to recharge the core. Spliced terminations would be wormed, parcelled with tar soaked calico and served. The condition of the wires and splices could be monitored and replacement planned.
Stainless steel is different in that it shows little sign of ageing compared to ordinary steel. It corrodes in hidden places when deprived of the oxygen which enables the passivating layer of chromium oxide to form. Terminations are not hand made splices as before but machine made cold headings and forgings. Stainless steel is also subject to fatigue due to work hardening and cyclic stress loading. None of these defects can be seen to observation in normal use. The spar maker Per Selden tried to establish some kind of applicable measure of service life to stainless steel yacht rigging.
In the 1960’s he tabulated the data that was starting to be recorded on stainless steel rig failures and came up with a figure for typical safe service life of 20,000 miles. This data also generated the ‘bath curve’. This is a graphic representation of rig failure and can be imagined as the side profile of a domestic bath. The tap end is vertical and represents a high initial incidence of failure due to faulty manufacture or defective materials. The curve then runs flat along the bottom of the bath until after about 20,000 miles the curve rises slowly as failures start to occur from corrosion and stress fatigue due to cyclic loading and work hardening.
Some insurance companies jumped on this figure for policy terms, but as there was rarely any record of the usage of a vessel that they were insuring, they simply estimated annual usage at 2,000 miles, hence the infamous ‘ten years’ came into common usage with little real logic for time alone to become a sensible measure. In the present day of typical leisure use, the majority of private yachts do not get anywhere near 2,000 miles per year, whilst a very few could do 20,000 miles in a couple of years of blue water cruising.
Rig surveys are therefore a combination of the assessment of the visible condition and the evidence of the type and extent of the recent use of a vessel. Rigs that have been unstepped or de-tensioned annually during lay-up will usually be considered to have been maintained in better condition and likely to have a longer service life. The wire itself is very rarely the cause of failure which mostly occurs in the terminations or the chainplate structure. These can often be due to faulty manufacture or poor installation which can be identified by survey.
So, the age can give some indication of the length of good service life remaining in a rig, but it is only one factor in a complex assessment. Surveyors will usually make recommendations based on many factors which can suggest the potential for failure. These include the type and extent of use a vessel has had combined with physical checks of the condition of the standing rigging, Poor installation can be seen in the line of load to a termination, the correct sizing of cotter pins to forged fittings, the correct matching of forged or cold formed heads to mast fittings and measuring the roll or rotary swages to the standard tolerances.