stainless rigging wire - nick in wire
 

On Oct 8, 9:41 pm, Wayne.B wrote:
On Mon, 08 Oct 2007 18:22:30 -0700, Frogwatch
wrote:

I wish I'd gone with Norseman or Staylok instead of swaged terminals
when I rerigged. From what I see on the web, they last much longer
with no cracking of the swaged area.

I think that's a good plan if you have a way to load test them to SWL
off the boat. Otherwise you really need a *lot* of confidence in your
workmanship.

I am an expert at overestimating my abilities.

stainless rigging wire - nick in wire
 

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

stainless rigging wire - nick in wire
 

Subject

Haven't done any serious cable design for many years.

That said, cables have their applications but are designed with
serious safety factors applied.

The weakest point of the cable design is the termination and/or the
splice.

In addition, hidden corrosion at the termination also weakens the
cable system over time.

One of the biggest unknows in cable design is fatigue failure due to
vibration induced by the winds.

Just ask any electrical power distribution company why they have all
those funny looking things hanging on their cables in what appear to
be unusual positions.

(One of my fraternity brothers was chief engineer for a company that
helped solve many of the cable fatigue proplems.)

Those same fatigue failure problems apply to sailboat rigging.

Bottom Line..................................
There is a hell of a lot we don't know about what happens to a cable,
when loaded, thus BIG saftey fsctors are required.

Lew

stainless rigging wire - nick in wire
 

On Mon, 08 Oct 2007 19:47:26 -0700, Frogwatch
wrote:

I think that's a good plan if you have a way to load test them to SWL
off the boat. Otherwise you really need a *lot* of confidence in your
workmanship.

I am an expert at overestimating my abilities.

=====================================

Aren't we all. Boats have a way of finding us out however.

:-

stainless rigging wire - nick in wire
 

"Brian Whatcott" wrote:

Now THERE'S an interesting question!
How would an engineer want to specify the rigging for a sailboat?

With an eye on the budget.

Find a similar boat and see what it is using.

Use that size as a base, then increase it one size jut to CYA.

End of design.

In the USA, material is cheap, manpower is not.

It is something you learn very early, if you want to continue to be a
design engineer.

Airplane design is a totally different story.

Lew

stainless rigging wire - nick in wire
 

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

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?

Except for a roll over and no rig is designed to withstand that.

Professional experts and engineers use the righting moment of the boat
to determine rig loads. Sail area is largely irrelevant. A fudge
factor for shock loads and a safety factor is also necessary of
course.

I don't know how rigging wire is specified but I do know that anchor
chain and rode is usually specified with a Safe Working Load (SWL) of
approximately 20 to 25% of breaking strength. Sometime after SWL is
exceeded, but before breaking, the material in question will exceed
its elastic limit and permanent elongation will occur. That's a
particularly bad thing for chain which is sized to fit the pockets in
the windlass gypsy. It would also be a bad thing for rigging wire
because it would leave the mast badly out of tune.

stainless rigging wire - nick in wire
 

Jere Lull wrote:

Come to think about it, I don't believe our jibs have wire luffs, but
even without it, the bolt rope and material would do the job for a short
bit.


No, actually it wouldn't.

Not unless it was at least the size and strength of the forestay -
and tightened the same or tighter.

If the forestay failed that boltrope won't even slow it down...

Richard

stainless rigging wire - nick in wire
 

Lew Hodgett wrote:

"Brian Whatcott" wrote:


Now THERE'S an interesting question!
How would an engineer want to specify the rigging for a sailboat?


With an eye on the budget.

Find a similar boat and see what it is using.

Use that size as a base, then increase it one size jut to CYA.

End of design.

In the USA, material is cheap, manpower is not.

It is something you learn very early, if you want to continue to be a
design engineer.

Airplane design is a totally different story.

Lew



Good, Lew! :)

stainless rigging wire - nick in wire
 

Wayne.B wrote:

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


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?


Except for a roll over and no rig is designed to withstand that.

Professional experts and engineers use the righting moment of the boat
to determine rig loads. Sail area is largely irrelevant. A fudge
factor for shock loads and a safety factor is also necessary of
course.

In other words, a safety facor of 4 to 5.

stainless rigging wire - nick in wire
 

Jere Lull wrote:

Since when does 17/19 become 20%?


You're right. Should be 10% (2/19 rounded). (I was up WAY too late after
a great sail that brought the bow past the outer breakwater as the sun
kissed the horizon.)

Yes, the stay is probably okay, but I don't play around with the
forestay in particular. The OP *saw* two nicks. Are there perhaps others
he hasn't noticed?


My first thought on the filing of wire strands was -

How much damage would that do to the rest of the cable?


Anybody really think they can dress out two strands of cable - IN the
cable - and not touch any of the rest of them?

You know, the most interesting part of this story has not been told yet!

How did the hacksaw just happen to nick a couple of wires?

There has just GOT to be more to that one...