Work hardening and crevise corrosion
There are two things that kill rigs.
Crevice corrosion is the #1
Work hardening is the #2
(However these two are actually connected as either exacerbates the other)
Way down in points is physical abuse at #3
Storing the mast up in a yard is horrible. All of the wind forces are substantially higher than a boat on the water. There is no flex or flow in the system. Also you are taking out any dampening ability of the rig at the time when the non sailing loads on it are at the highest, that is in the winter when the wind is more severe. Rigs that are left up in the great lakes are good for about 10 years maximum before they have work hardened to the point that they are subject to failures due to flexing. Every single wire rope manufacture states the same. Standing rigging left aloft is good for 10 years. This equates to about a million or more flex cycles of the wire at the terminal junctions and spreader ends. The greater the flex cycles the shorter the wire life. Leaving the mast up during the winter lay up frequently causes larger and more flexing that occurred during an entire season of Aggressive racing).
Yes you will see rigs up in the great lakes that have been hugely abused for 40 years. What has changed is the safety factor. When we as riggers design a rig we realize that we cannot foresee every possible real world situation that may occur. So when the rig is designed there is a 5:1 safety factor that is used in it's design. That means that we know that there are going to be situations outside of the normal that will apply more force to the rig than we can easily or reliably calculate. Shock loading, overloading, sail strikes while overloading, center loading of a piece of standing rigging, falling off a wave while over canvased, and a whole host of others. The 5:1 safety factor seems excessive until you start to calculate the load on a cap shroud when the crew has screwed up in a gust, laid the boat on her beam ends with the foresail backed against that cap shroud, such that we are now loading the cap shroud in the middle of it's unsupported length. After about 10 years with a rig up you have reduced the safety factor to something less than 1:1. It is all about the repeated flexing of a material.
I used to have a large box of standing rigging that had been up for 30 years each coupled with a piece that was brand new. I would hand them to people when they asked about this. (The best for this demonstration is 7x7 steering cable that has been installed in boats for 30+ years, but all of the standing rigging works. (It gets cycled more as it moves around the sheaves, and so is very hard compared to new cable.) I would then ask them to bend the two pieces in their hands. You can feel the difference it is substantial. You are feeling the work hardening of the material.
Crevice corrosion does happen and should be inspected for in the great lakes, but it is not at the rate on as happens on a salt water body. Still you should inspect for it.
Now if you take the rig down every year, and clean it and store it correctly. Then you have 1/3 of the flexing of the rig that you would have if you left it up. That is pretty simple math, the rig is going to last 30 years, maybe more. Also every year the rig is going to be completely inspected with the tear down and cleaning, which is going to result in worn parts being replaced and problems in the rig being seen earlier than if the rig is up. So the rig has the potential to last 30 years on the great lakes. Also the mast is cleaned and stored correctly, it's coating is generally much preserved over one that has been left up. I have seen 30 year old running rigging on the great lakes that was ancient technology, but was still like new because it had been removed every year. There is no good argument for keeping a mast up in the off season. Most of the great lakes areas are very inexpensive for mast removal at the end of the season as compared to the cost of wear and tear on everything. (The boat also suffers when the wind hits the rig while the boat is on jack stands).
On the ocean in the tropics with new wire I am seeing 5 year life cycles in SS wire. 7 is too long with dramatic failures taking place that endanger the crew and vessel.
More temperate climates like Northern California through British Columbia we are seeing rigs last 10 years or so, (Boats on the west coast are almost always left in the liquid water all year long). The work hardening and crevice corrosion generally damage these rigs at about the same rate. A little less crevice corrosion in Seattle and BC, but still sufficient work hardening to recommend their renewal at a 10 year schedule.
The Ericson 46 that I am sitting on was a great lakes boat and had the rig pulled every year, and stored in a heated barn. The rig was 1972 - 2005, 33 years old when we bought it. The wire was work hardened, and did have a few broken strands because of it. (By the time you have broken strands in a rig you have been living on the edge way way too long. You should buy a lotto ticket you have been so lucky). I could feel and measure the difference between the old wire and the new wire on my boat, and it was one of the best kept I have ever known. (Never upgraded, but kept wonderfully! LOL ).
Yes your 30 year old boat needs new rigging so that you stay safe. You have a less than 1:1 Safety factor at this point in time. However most people I know on the great lakes refuse to believe any of this till there mast falls over... Just one of the cultural things...
From Navtec one of the manufactures of the wire in discussion:
http://www.navtec.net/ (Support, then download the pdf wire rigging maintenance)
"Navtec estimates a life expectancy schedule based on climate variables and water salinity:
Heat and water salinity at maximum (Florida, Caribbean Islands) - 5 to 10 years
Heat and water salinity at medium levels (East/West coast of US) - 10 to 15 years
Fresh water climate - 15 to 20 years"
Guy
P.S. I grew up sailing and working on boats in the Great Lakes. The west coast is now my home, but I didn't start out here!