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Re: Islander 36
Replacement of the standing rigging (rod, cable, terminals, all of it) is really based on several factors that are not easily measured on any one boat. There is the quality of the metal, assuming nothing is counterfeit which you can't assume these days. Then there are environmental effects, how much salt, moisture, heat, thermal cycling, any coatings to block oxidation, any wrappings to rap water, etc. For the rigging itself the single greatest issue may be work loading, i.e. as the cable or rod stretches under load, then eases off as you tack the other way. Every load cycle brings it closer to failure.
In the north you also have problems from water getting into joints and swages, and then freeze expanding over the winter. This breaks down mountains so rigging is not going to endure it either.
All of these things vary greatly depending on the use of the boat, and NavTec even goes by how many miles a boat has sailed, as a rough way to correlate to work load cycles. None of these factors would be hard to measure in a lab, but in the real world? Who knows what a used boat really went through?
You can of course test the rigging with dye checks, or pull it and have it magnafluxed and x-rayed. But for most people, the cost of doing that brings you to a point where it is not practical, and as long as you're pulling the rigging, it becomes easier to pick some "not unreasonable" point like 10-20 years and say OK, I'm going to replace the rigging now, all of it. Based on your best guess as to how it was used, on any visible signs of deterioration, etc.
With wire rigging if you find any meathooks--even one--that's a sign wire strands are breaking, time to replace. With stainless fittings, if you find even one crack, again, that's a sign, time to replace. If you are sailing in a lake in moderate weather and a failure would simply mean "Honey dinner will be late" you can put it off longer. If you're oging offshore and can't be certain of kind winds and smooth seas...safer to use the calendar or replace at the first sign of deterioration.
Until Walmart starts selling home xray inspection kits, that is. (G)