Wednesday, November 5, 2014

High Modulus Polyethylene

There have been a lot of changes in the approach to standing and running rigging in recent years with the introduction of high modulus polyethlyene line such as Dyneema and Spectra. There are lots of pros and cons relative to wire and traditional line which I won't go into but in summary, it's lighter and stronger though less chafe resistant.

This summer I began making some changes to Jeroboam to take advantage of the weight savings by using soft shackles as replacements to metal ones, replacing the wire lifelines with dyneema and reconfiguring my backstay with a cascade to replace the hydraulic backstay adjuster which was completely overkill for Jeroboam (not to mention heavy).

Here are some examples of soft shackles:

From the left, the first is made from 2mm FSE Robline MRX dyneema and has a breaking strength of approximately 1,000 pounds. The middle one is made from 1/8" Samson Amsteel AS-78 and has a breaking strength of approximately 3,000 pounds. The right one is made from 3/16" Sampson Amsteel AS-78 and has a breaking strength of approximately 6,500 pounds. With the right tools and a little practice, they're easy to make. This website contains a lot of good information.

I added the hydraulic backstay adjuster in the fall of 2012 when I installed the new mast. It's a Saletec 17LI long stroke adjuster capable of 8,750 pounds of tension.


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Low Friction Ring



It's completely overkill for Jeroboam, which isn't a stiff boat to begin with, so I worked up a new design that uses Antal low friction rings in cascade and a single block with becket and cam to tension. I used a single strand of 3/16" Samson Amsteel AS-78 with New England Ropes dyneema chafe sleeve from the mast head to about two thirds of the way to the deck, then split the backstay from there and added the cascade pictured below:




The adjustment takes place at the bock and cam, shown left and the pic on the right shows the the whole set up.


The lifelines are made from 3/16" Samson Amsteel AS-78 with New England Ropes dyneema chafe sleeve used only at the stanchions:


Word on the street is that dyneema lifelines are in the process of being re-reviewed by ISAF. Previously they were allowed under the offshore special regulations (which apply and/or influence rules for OSTAR, Bermuda 1-2, Halifax and others I've entered) but I hear an ISAF working group is reconsidering their stance.

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