Synthetic Standing Rigging
Synthetic Standing Rigging |
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Perhaps today's materials and yesterday's techniques will create the rigs of tomorrow...
I'm thinking about what it would take to rig a taditional-style, heavy-displacement sailboat (30-40 foot range) with synthetic standing rigging, for long-term cruising. Perhaps surprisingly, one thing I've discovered is that I'm not the first person to think about this... maybe I'm not mad.
Of course, this concept -- and the fibres it's based on -- are far too new for anyone to have any kind of long-term usage information; so this is still very speculative. Bearing this in mind, here's a quick survey of the state of the art...
Why go to synthetic standing rigging?
Why not? Three problems seem to crop up:
Cost is also an issue, of course. I've put together a very rough cost comparison, which seems to show that a new synthetic rig is comparable to a steel one; however, the fact is that I have a steel rig right now, and even if I write off the wire, re-rigging with synthetic would be a big deal -- mainly because I would be chucking out about $850 worth of good turnbuckles.
Obviously we want to keep stretch within "reasonable" levels, otherwise the lee shrouds are going to be flopping all over the place. And we want something strong -- over-sized stays are a bad idea, because of the huge extra drag this would entail. Not that I'm a performance freak, but the additional noise and vibration has a massive effect on the perception of conditions at sea... recently I was sailing on a large ketch in a huge gale, fretting about whether we were going to have some unwanted excitement -- when I realised that the wind was just 20 knots! On my own Westsail 32 on SF Bay, in 20 knots, I'm whistling for wind!
So. On the face of it, PBO fibre would be perfect in terms of stretch and strength; but from what I gather, it's so UV-sensitive that even covered PBO fails very rapidly in sunlight -- in terms of how rapidly it "goes off", I've seen it seriously compared to milk. Boats (racers) rigged with PBO apparently use a solid plastic cover over the rope for extra protection. However, given the innate UV sensitivity, PBO would not be my choice for tropical cruising.
This leaves Vectran and UHMWPE (Spectra/Dyneema). Vectran has no creep, but the word on the docks is that it's rather UV-sensitive. UHMWPE creeps, but seems to be quite good against chafe and UV.
To me, Dyneema SK75 looks like the best fibre around right now, in terms of being reasonably chafe- and UV-resistant, and lower-stretch and stronger than Vectran; the only issue being its tendency to creep. SK75 is supposed to have less creep than earlier UHMWPEs, though; SK78, even less so. Anecdotally the creep of UHMWPEs has not been a noticeable problem in practice; but this is based on its use in running rigging. I would think that it would be more of an issue in standing rigging, unless you slack your stays off after each sail, and then re-tune the mast next time.
Of course, I don't know how chafe- and UV-resistant any of these fibres are, due to the lack of any organised testing (as far as I know). Still, it seems that the newest fibres may be up to long-term use; particularly in covered rope form. Obviously one would use extra chafe protection, like leather patches, in problem areas. But hey, you can fasten stuff to your rigging without it rusting! Cool!
Of the various ropes on the marked, Hampiđjan's Dynex Dux 75 looks really cool; they claim extra strength and less creep than the Dyneema SK75 base it's made from. It's uncovered, but it would be easy enough to add an off-the-shelf cover; Marlow's MGP Nomex should offer even better chafe protection than polyester. Does the Duracoat coating on Dynex match the Marlow/NER etc. coatings in terms of UV protection?
Some synthetic standing rigging -- notably PBO -- is terminated with glued mechanical terminations; I think this is to keep the rope completely protected from UV, and for compatibility with existing rigging systems. However, other people are of the opinion that good old eyesplices work best (which is what I would have assumed). Apparently rope is tested with eyesplices as the terminals; hence (if true), the rated strengths for ropes include the 10% weakening imposed by the splice.
How to get the tension on the rig? Most of the people using fibre rigging are racers, and want to get rid of their turnbuckles for weight reasons. But as far as I can see turnbuckles won't work anyhow, because the initial "bedding-in" elongation, coupled with the higher stretch of synthetic, will make them impractical.
The concensus is that deadeyes and lanyards are best -- specially with Precourt's new aluminium deadeyes to support this. And nice and traditional, of course! How about marrying Dynex Dux 75 UHMWPE and an MGP Nomex cover with deadeyes in lignum vitae?
One big question: what about the forestays? How to hank on sails (assuming no roller furling) without causing chafe on the stay? Precourt have "soft hanks", which are basically Dyneema SK75 loops attached to the luff of the jib, with a toggle to allow them to be quickly fastened to the headstay. They are recommended for both steel and synthetic rigging. They look like they might chafe out themselves fairly quickly; but they'd be easy to replace. Equiplite have some simliar systems.
How to measure the tension on the rig? Or is it more touchy-feely?
SSB performance should be improved! The usual technique of using an insulated backstay for an SSB aerial not only adds weight and cost to the backstay (via the insulators), but doesn't work terribly well, due to the mildly poor conductivity of stainless steel and the problem of the connection to the backstay, which involves a junction of two metals (copper and SS) and is exposed to the weather.
With a synthetic backstay, there should be no problem (as far as I can see) with running an insulated copper cable up it (even inside the cover?), which would connect to the antenna tuner below deck, out of the weather. I don't think you can do this with a steel backstay, as trying to transmit from a copper wire which is clamped to a grounded steel wire looks like a bad idea -- but radio antenna design is a total black art to me.
Copyright (C) 1995-2006 Ian Cameron Smith.
visits since 20Sep06.
Last modified: Tue May 15 18:11:19 PDT 2007 ($Revision: 1.1 $)