Makes no difference
Being in fresh or salt water makes no difference due to atmospheric contaminants .... being downstream of a powerplant, large highway, acid rain, etc. are sometimes WORSE. GUESSING, wringing your hands, etc. will not get you anywhere, Even total replacment of the rigging with new will not give 100% assurance that the rig wont come down (inbuilt materials defects or human error). Most metals including and especially 300 series stainless are materials that have a 'generalized' lifespan when subject to cyclical stress ... something to the value of 1 million load cycles when the material (300 series stainless) is subjected to above 30% of its Ultimate Tensile values. Such materials when repetetively stressed ... simply get 'tired' (fatigue) and lose their strength ... thats why there are junk yards for automobiles and airplanes and ships - they got 'tired'/fatigued. So what can the 'average person' do to validate 'some' structural integrity of their rigging? The simple answer is occasionally PROOF LOAD it (although Proof loading does include some measure or exposure of personal danger ... so Im not telling you to do this, just describing what I do). A DIYer can do this with a simple rigging tension gage; some of the better rigging shops can offer such services (although the price of testing can be as high a new rigging), university mechanics/material labs sometimes will do this, commercial testing labs (again with cost). You can also take the components to an 'automotive machinist' to have the parts, etc. 'magnafluxed', dye-penetrant testing of the terminal ends, etc. to assay for fatigue (can do this yourself), etc. Two main modes of FAILURE: 1. Ductile failure ... where the metal is loaded beyond 'yield' and the result is that the dimensions change permanently. If you carefully measure NEW RIGGING (after being in service for a short time to insure that the 'dimensions' have 'settled-in' to their final new lengths, etc. ..... the wires have to 'work' into their final resting state, etc.), carefully measure the length under a low load (~10% of ultimate tensile strength - use a rigging tension gauge) you will have a benchmark reference for later measurement. When checking in the future (and with the same 'preload' applied) if that (length) dimension has changed (becomes longer) then there is ductile failure (yield) in the assembly then you have YIELD and that signifies FAILURE. If a swage has slipped, etc. this also would show as a 'changed' length. Any 'localized' deformation caused by 'yield' would also be deemed 'failure' .... deformed rigging eyes, clevice pins, bent deformed toggle (T) bolts etc. ... such localized failure 'can' be locally replaced remedied OR the whole assembly replaced. Therefore for DUCTILE failure ... any dimensional change is a FAILURE. If you keep accurate records using these as a reference, you can quite accurately make a very close to accurate decision in the future when you 'remeasure'. All you need is a rigging tension gage, a long steel tape measure, and accurate records. 2. Fatigue (includes crevice, etc. corrosion) Any metal that is stressed will begin the fatigue process at the FIRST loading .... the formation of microcracks along the microscopic 'grain boundaries' within the metal. This process of cracking is ADDITIVE and continual; the more you stress the metal the more microcracks you accumulate. 300 series stainless is especially prone to stress cracking / fatigue. Originally 300 series stainless was conceived for the chemical process industry ... for corrosion resistance properties. Only after 30-40 years do we begin to KNOW the behavior of 300 series stainless (this is the most common stainless used in rigging); so many of the boat designs (rigging) were (then) based on a material that wasnt clearly understood at that time of the original component design. Each metal has a physical property called Endurance Limit .... a value of stress when the metal is NOT loaded above will be (generally) suitable for infinite service versus fatigue ~infinitely. Inotherwords if you do not stress the metal above the 'endurance limit' the accumulation of fatigue will not occur to approach FAILURE. The fatigue/endurance limit of common 300 series stainless steels is approximately 30000 psi. .... about 1/3 the value of the ultimate tensile strength; if you carefully do not load the stainless above 1/3 of its UTS, fatigue is reasonably kept in check (but there are local 'anomalies' and design 'traps' that can lessen the usefulness of the metal therefore the endurance limit is not 'absolute'). A double whammy on boat rigging with 300 series components --- Once the micro cracks of fatigue form they leave an 'opening' for corrosion to begin within the boundaries of the microcracks. Moisture (vapor mostly) penetrates the cracks, crevices, the metal absorbs the oxygen out of the vapor/liquid and corrosion begins on a macromolecular level (crevice, etc. corrosion). The more corrosion forms, the weaker the metal; the weaker the metal the easier for more microcracks to form when the material is stressed and a viscious cycle begins until the metal catastrophically (suddenlly and without warning) fails. Visual Inspection for fatigue: any small visual 'cracks' that appear on the surface of the metal, any 'haze' or loss of 'shine'/smoothness on the surface or any zones (especially near welds, or 'bends' or 'holes', or 'edges' that are showing 'rust'. Its really better to use a high power magnifying glass or pocket microscope (RadioShack used to sell them) to 'look'. If the part is in 'doubt', then you can yourself perform a Dye Penetrant Test on all the 'terminals'. The test pack contains a Cleaner, A penetrating dye, and a developer. West Marine used to sell it and can probably still 'special order' it for you. The dye penetrates into the microcracks, the surface is wiped clean, the developer is sprayed over the part. If there are cracks the dye will absorb from the crack back into the developer (a chalklike substance) and a 'diffuse pink line' will appear over the crack in the developer, no crack and there will be no dye to absorb into the developer. Caution... the dye will deeply penetrate into gel coat so this is all done OFF and away from the boat. Any part that develops the 'teeny pink lines' in the developer, etc. is probably fatigued. You're Not done...... Since developed fatigue also potentially weakens the structure you can 'proof load' the rigging (while using a tension gage) to a relatively high load to discover fatigue that is not 'showing' on the surfaces. Caution - if rigging is loaded to a high % and fails you are at risk to be injured, etc. by the 'snap back' .... I do all the 'proof loading' with my body OFF the boat if possible. I tie the mast addtioinally with halyards, etc. so if a shroud, etc. unexpectedly breaks during the proof loading, the mast doesnt go down/overboard, etc. I load a shroud, etc. manually using a rigging gauge to ~60% breaking strength of indicated load (most Loos gages have these values imprinted ON the gage vs. the wire diameter) ... then I wrap/tie a stout line somewhere near the middle of the shroud and pull the line PERPENDICULAR to the shroud with a winch, etc. (standing nowhere near the shroud in case of 'snap back').... I apply tension to the 'rope' with a winch, etc. while I watch the gage with a binoculars (from a safe distance) until I reach about 75-80% of the breaking strengh as indicated by the gage. For shrouds that require me to be 'close' I put 'slotted' pvc pipe over them to help contain the possible 'snap-back'. Ive discovered several BAD shrouds, terminals, swages, etc. & Ive even broken NEW rigging with this method. Once Im satisfied with the proof loading, then I inspect for the telltales signs of fatigue, then measure to the 'original' dimensions. I ususally do this every 4-5 years or before a long passage. Many 'good' rigging shops will do this proof-loading for you (especially if you dont want to needlesly expose yourself to the dangers of 'snap back' etc.). Proof loading with such crude methods isnt 100% correct ... but it does 'raise your level of confidence' a wee bit more than 'replacing every 5 years. Run away from: "I sailed 30000 miles with mine so you can too, "I used to build boats", self-promoters, etc. etc. etc. etc." Expect the rigging to totally fail after one circumnavigation or equilvalent (1 million load cycles), sooner if the boat is sailed 'hard' (heeling a LOT at 30-45 degrees over), and/or you've been applying humongous backstay tension to keep good shape of the headsails, etc. Any length change = failure Any bent or deformed terminal = failure Any chainplate that's beginning to show ANY visible change- 'dulling', tearing, rust, hole elongation, etc. = failure Any change of 'sheen' or 'shiiney-ness' on the metal = failure Any visible cracks (includes die marks from swaging errors)= failure Any 'rust blooms' - probable failure getting ready to happen Any rig that cant pass a simple crude proof-load to 70% of the tensile value of the wire = failure. Still, nothing beats the practiced eye of an experienced rigger on an 'up the mast inspection' every few years - very inexpensive insurance. They (should) KNOW what's crap and whats 'good' and have the 'eyeball' experience. Lastly, contact your (large) insurance carrier who has volumes of historical data on your particular boat/designer/yard .... if the original design, etc. was substandard there WILL be evidence of 'claims', etc. Also join an internet 'owners group' for your particular boat ... they will sometimes also have the 'historical' data of 'what worked, how long, etc.' Get a 'good' rigger up your mast every now and then (even if you do all your own work/testing, etc.) ..... cheap insurance. If you develop a good constant working relationship with a rigger ... will pay dividends. hope this helps.
