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Synthetic Rigging

PostPosted: Sun Jun 04, 2017 2:03 am
by TassiePete
I had a very interesting meeting with a local sailmaker re a set of sails for the PS. The most interesting part of the discussion was the question, why I would bother with 9x17 wires for the stays ( both, mast- and bob- ). An equivalent 4mm Spectra line ( Dyneema, or the like ) is stronger, much lighter, soft ( it doesn't attack the paint work ), less expensive/easier to install. Obviously, the appropriate knots and splices will have to used. Spectra even comes in a silver colour! I am seriously considering this option. Does anyone know, whether there are there any particular reasons that steel is necessary in this application ?

Cheers,

Peter

Re: Synthetic Rigging

PostPosted: Mon Jun 05, 2017 7:30 am
by craig
I didn't think to do that. It would save a lot of money (the swageing tool, wire, fittings, etc). Make sure you get one that is as strong as possible! And watch for chafing damage obviously.

The most important thing I've discovered on Pocketship is to properly tension the shrouds (the forestay will be tensioned by raising the jib, so it doesn't matter). My stays were tight but not VERYTIGHT when I first launched, and a day of really big wind caused some damage to the bulkhead. Now that I've tightened down the shrouds I haven't had any issue whatsoever. So I realize that spectra is low stretch, but if it stretches more than wire rope (??? presumably?), take that into account when you are tightening everything.

Re: Synthetic Rigging

PostPosted: Mon Jun 05, 2017 9:44 am
by mark48
Hi Craig,

Are you using turnbuckles between the shrouds and the chainplates - or the 2mm Spectra line used in PS #1 - and if so, can you tell me what turnbuckles you used?

Thanks,
Mark

Re: Synthetic Rigging

PostPosted: Mon Jun 05, 2017 10:02 am
by craig
I have turnbuckles but haven't put them on yet. Unfortunately when I did the rigging I made the shrouds too long, so when I later got a pair of turnbuckles I couldn't fit them to the boat. I plan on buying a new set of swage parts and cutting my shrouds to fit, but haven't done that yet. What I did to make sure my rigging was tight was wrap a couple loops of line through the Chainplate in the cabin wall, and through the shroud ending. Pulling that tight, with all the force multipliers of the several rounds of the loop, made it good and tight.

Re: Synthetic Rigging

PostPosted: Mon Jun 05, 2017 4:27 pm
by TassiePete
Stretch for Spectra seems not to be an issue until about 30% of the rated load. For low values, the stretch is about the same as for a steel cable. When the load goes up, the stretch is somewhat higher, but still a lot lower than for any other material ( including pre-stetched varieties ). The loads on a PS are reasonably low, but it is always possible to go up to 5mm line, which will almost double the max load ( and half the anticipated stretch ).
The biggest issue with low tension of stays is that any side-ways load on the mast will be taken up ( or not ! ) by the tabernacle, instead of being taken up largely by the windward shroud. On the other hand, a huge pre-tension on the stays will cause a tremendous compression force and make the whole rig very stiff. I guess ... it is a matter of tuning. If everything stays aloft in all weather conditions, then the setup is right.
I agree, it will be necessary to inspect these lines occasionally for wear. Then again, steel cable doesn't last forever either, and replacing Spectra lines will be less of a hassle than replacing wire cables.

Re: Synthetic Rigging

PostPosted: Mon Jan 07, 2019 2:37 pm
by Shudoman
I'm thinking of retrofitting my PocketShip with Dyneema. Has anybody done this? Or are we still in theory land? :D

Regards,
Bill

Re: Synthetic Rigging

PostPosted: Fri Jan 11, 2019 1:58 am
by TassiePete
Hi Bill,

I am using Dyneema (4mm) for the shrouds and the bob stay (6mm). The reason I used 6mm for the bobstay is for looks only - the 4mm line just looked out of place. For the shrouds and the bob stay, I spliced eyes on each end (brummel self-locking) and used cow hitches (think luggage tag) to attach the lines to the hardware. The shrouds (at the bottom) and the bobstay (at the sprit) end in welded steel rings. The rings end up about 5" short. From there a few turns of 2mm Dyneema tighten up the rig. Everything is working fine.

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Cheers,

Peter

Re: Synthetic Rigging

PostPosted: Mon Jan 14, 2019 9:28 am
by Shudoman
Thanks Peter,

You've given me a couple of ideas on how to approach this. I've ordered the dyneema and it should be in sometime this week. Looking forward to this project.

Bill