On Tue, 09 Oct 2007 02:50:57 GMT, Brian Whatcott
wrote:

On Tue, 09 Oct 2007 01:58:09 GMT, (Richard
Casady) wrote:

... Most
failures of standing rigging I've seen happen at the fitting which is
less strong than the wire. Thus if you have a wire section at 90% of
strength, it's probably still not the weakest link.
...
What is the safety factor? That is the real question. If it is large
that would be one thing.

Casady


Now THERE'S an interesting question!
How would an engineer want to specify the rigging for a sailboat?
He might want to consider the peak loads applied to the rigging.
What could that be?
Perhaps it would be the gale that puts the main mast and sail parallel
to the water? The rigging forces could hardly get greater, possibly?

That would not be too difficult to measure, surely?
How about taking a main halliard offboard, abeam the mainmast, and
hooking it to a winch to pull the mast down, with a force meter
attached?

Not quite the distributed loading you'd get from the wind, but a
measure, all the same. Perhaps he would have the test repeated, with
the force applied 45 degrees forward of the beam, and then repeated
with the pull applied 45 degrees aft of the beam.


These are not diffficult tests to apply, surely?
Then an engineer would want to apply a design factor to account for
the variability in wire and fitting strenth as new, and during
service.
It might be a factor of 1.3, it might be a factor of 2.

Then he would compare his peak (factored) stresses against available
rigging wires, and pick the next convenient size larger. Bingo!

Or instead, he might choose a rigging size that is considerably
cheaper and slimmer, and declare the boat as "inshore" or "coastal".
Who knows?

Brian Whatcott Altus OK

Essentially the strength of rigging based on the effort to heel the
boat to its self-righting point times a safety factor.

Any boat design or professional rigging handbook should have the
calcs.

Or, ask Roger - this should be right down his alley.


Bruce in Bangkok
(brucepaigeATgmailDOTcom)