Tom --- simply go back to basic structural engineering basics.

All metal has a service life based on fatigue. Even below the
endurance fatigue limit, applied cyclical stress will develop
microcracks between the grain structure. Such propagation is minimal
but continuously additive to applied cyclical stress. At or above the
endurance limit the fatigue become more 'predictable', below the limit
the fatigue is 'not so' predictable. The inevitable failure for ALL
metals in cyclical stress service is embrittlement and crystaline or
fatigue failure. Fatigue failure at scantiling design values with
Safety Factor of 4X (typical ocean service) still but rarely happen.
Only when the stress design approaches FS=6 does fatigue failure
become rare; but rare doesnt exclude some failure. I repeat: The
inevitable failure for ALL metals in cyclical stress service is
embrittlement and crystaline or fatigue failure ... this WILL
eventually happen to rigging, rigging supports and keel bolts on
boats.

At stresses less than that the bolts will essentially never fatigue,
right? *I'm looking at a worked example of an ABS keel bolt
worksheet. *Since you're using psi I'm converting to USA units. *10
keel bolts of 0.83" (at the thread root) support a 7,175 lb keel with
a cg 2' below the joint. *Even assuming half the bolts aren't doing
anything the maximum static stress on those bolts are going to be an
order of magnitude below their endurance load. *Hydrodynamic loads on
the keel max out at about the same order. *Day in and day out you'll
never approach the endurance limit of ABS sized bolts. *On top of that
your typical designer is going to use the next size up off the shelf
rod. *As you'd expect with those kind of scantlings keel bolt failure
is extremely rare. *Fatigue isn't normally an issue.

... *That sailboats constantly have to
have rigging replaced, on some - keels & rudder shafts, etc. keep
falling off ... would tell any prudent engineer/designer that
'something is wrong' in the 'typical design'.

Rigging is a different story with very different compromises. *Keel
failure is so rare that I think each case needs to be looked at
individually. *There is no evident systemic problem with keel bolts as
a class.

-- Tom.