On Jun 10, 1:36 pm, RichH wrote:
....
once 300 series stainless gets loaded above its endurance limit it
typicallly only lasts approx 1 million load cycles - doesnt matter if
its rigging, keelbolts, chainplates. If the endurance load factor (at
about 30kpsi) is exceeded, 1 million cycles is about all you get...

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.