[MHml] mast woes

[Bill Gibbs]

Charles,
The mast designer made similar comments on this topic #2.  It may be strong
enough.  He also commented that he/they were surprised at the stress levels
measured by strain gages on the diamonds during tuning.  He also commented
that calculation of the stresses is more an art than a science.
 
Bill

  _____  

From: multihulls-bounces at steamradio.com
[mailto:multihulls-bounces at steamradio.com] On Behalf Of Charles Magnan
Sent: Sunday, October 15, 2006 11:44 AM
To: Informed discussion of multihull issues
Subject: Re: [MHml] mast woes


My comments/suggestions, for what they are worth:
 
1. try the nitronic and see if the mast breaks   It will probably be fine
when tested unless you test it in fairly extreme conditions, which will be
when you find out what it is really capable of, not a pleasant experience if
it is inadequate.
 
2. refit with larger nitronic rod Can you not first check the adequacy of
the newly installed rigging by calculations and only replace it if it seems
under strength? If the cobalt rods were surplus from a previous project they
were unlikely to be exactly sized for your boat and may have been over the
minimum required. I stress the word "may"!
Regards,
 
Charles


----- Original Message ----
From: Bill Gibbs <billg at gibbsCAM.com>
To: Informed discussion of multihull issues <multihulls at steamradio.com>
Sent: Sunday, October 15, 2006 6:40:28 AM
Subject: [MHml] mast woes


The riggers got my new rod diamonds installed Friday, mostly.  They had
trouble getting the original tensions back.  So I rang up the mast's
original designer in NZ, who suggested tensioning further on-the-boat, but
also offered to do some research with others involved in the original
project.  With typical yard efficiency and some high tide problems (we're a
little too tall for the crane), we get the mast stepped at the end of the
day.  That night there's an e-mail waiting for me with bad news.  The
original mast rigger remembers cobalt rod rigging, not nitronic.  Cobalt rod
is stronger and stiffer than nitronic, so a same size replacement is a
significant downgrade in strength and safety, perhaps too much.
 
History - Afterburner was built in '87 and modified/re-rigged in '92 or so.
Her owner and builders were tight with the NZ racing scene and AC program.
Many parts and sails were surplus from the AC program.  My first spinnaker
supposedly came from Grant Dalton.  Remember the 1988 America's Cup, and the
big white NZ1 versus S&S the cat?  After that loss the boat sat idle and the
program was discontinued resulting in a lot of surplus goods being sold
cheap.  Like the cobalt rod that was supposedly used in my diamonds.
 
I've asked the rigger to research a test to determine if my old rods are
cobalt.  Any suggestions?
 
Assuming it is, I have a problem.  Options include:
1. try the nitronic and see if the mast breaks
2. refit with larger nitronic rod
3. find a source for new cobalt rod.  One opinion is that it is no longer
manufactured.
4. refit the old diamonds and use the mast until it breaks from old age.
5. get a new mast  (1 & 4 end up here)
6. other?
 
All this because I act on the advise to replace 14 year old rod diamonds
before they fail.
 
On the good news side, the track replacement went ok, as did the new mast
winches, mast clutches, sail cars, and Precourt synthetic side stays.  So I
have a refurbished mast that may collapse as soon as I raise sails.  Sheesh!
Guess I should have researched the details before replacing the rigging.  I
"assumed" the rigger would replace with "same", whatever it was.
 
Suggestions?
 
Bill
Afterburner
 
 
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