Roger
That your present tangs have lasted this long only means you havent had 1M load cycles over 30ksi ... and therefore have remained 'under' the fatigue endurance limit (~30ksi).
Safety Factor of 3 is common for ocean boats; 90ksi UTS for normal 300 series stainless divided by FS 3 'usually' insures that one doesnt exceed the endurance limit of ~30ksi.
.... But, but, but, we all know that common rigging does eventually fail via fatigue; so, intuitively that FS should be increased - simply based on the quite common eventual failure of rigging. If the widespread rigging never or rarely had to be replaced due to fatigue then we wouldnt need to have such discussions.
As simple as I can put this: The fact remains that current FS=3 rigging does fail; therefore, more careful design a change of rig materials ... or increased FS is in order. If 'aviation'
had the relative high failure rates as 'sailboat rigging' ... there would be massive correction imposed.
BTW - Ive gradually increased all non-wire components where possible on my deep water rig to FS --->~4: plates, tangs, t-bolts, etc. etc. as I have had failures when I 'proof-loaded' them, thankfully at the dock and not well offshore. I proof-load my rig to 70% every ~two years.
That your present tangs have lasted this long only means you havent had 1M load cycles over 30ksi ... and therefore have remained 'under' the fatigue endurance limit (~30ksi).
Safety Factor of 3 is common for ocean boats; 90ksi UTS for normal 300 series stainless divided by FS 3 'usually' insures that one doesnt exceed the endurance limit of ~30ksi.
.... But, but, but, we all know that common rigging does eventually fail via fatigue; so, intuitively that FS should be increased - simply based on the quite common eventual failure of rigging. If the widespread rigging never or rarely had to be replaced due to fatigue then we wouldnt need to have such discussions.
As simple as I can put this: The fact remains that current FS=3 rigging does fail; therefore, more careful design a change of rig materials ... or increased FS is in order. If 'aviation'
had the relative high failure rates as 'sailboat rigging' ... there would be massive correction imposed.
BTW - Ive gradually increased all non-wire components where possible on my deep water rig to FS --->~4: plates, tangs, t-bolts, etc. etc. as I have had failures when I 'proof-loaded' them, thankfully at the dock and not well offshore. I proof-load my rig to 70% every ~two years.