PBO comes in lots of different flavours.
1) The Kiwis have bought reels of monofilament and wound their own shrouds up and down up and own, over two screws the right distance apart. This is then pulled up inside some kind of outer, with a loop sticking out of each end. Thimbles are then put in the ends and pigmented spabond or similar covers the fibres as they go round the thimbles. I like this approach, but we could not source the stuff in time. I now have the number of a supplier somewhere.
2) We have some braided PBO a lot like the VZ above. We use it for uppers, lowers and D2s. Shroud and forestay are stainless. We have had no trouble with these, and the mast lives outside. I made the terminations, and the uncovered parts are protected with heatshrink tube. We used metal thimbles. This approach makes for much stretchier shrouds than method 1 above because all the fibres are off-axis.
3) There are other on-axis methods with expensive terminations.
NB: Stiffness/weight is only half the battle - windage is a real issue too. One of the reasons that Vectran is probably ok for a forestay - apart from the lower working load - is that 5mm vectran has no aerodynamic penalty in the front of a jib (possibly a benefit), whereas that dia on a shroud would be a lot.
NB:
Modulus Vectran: 52-103 GPa
http://www.vectranfiber.com/pdf/8Pages%20from%20Vectran_broc_final61206-8.pdf Modulus 316 Stainless: 193 GPa
http://www.azom.com/Details.asp?ArticleID=2868 Modulus Carbon (NM): 200-325 GPa
http://www.geocities.com/CapeCanaveral/1320/ Modulus PBO: 315 GPa
http://www.mat.usp.ac.jp/polymer-composite/30th-yamashita.pdfNB - over a ~5m length of our 3mm steel shrouds we found ~12mm extension under 75kg, but over 50mm extension with the braided PBO, dia ~2mm. I did not do too many of these because the limits of the test rig were becoming apparent: The bannisters were creaking - possibly not just moving elastically.
