Idea for anti-torsion cable for diy top down furler

[cagey]

Been inspired by post by 2copplane 'DIY top down furler for 40 footer' and am gathering together the bits to have a go.
The anti torsion cable is fairly expensive to buy and anyhow I fancy DIY approach, so here is my idea to making one, please tell me where I have gone wrong before I start.
Boat is Sigma 362
Furler will be on Seldon retractable Bowsprit
Approx length of anti-torsion cable 14 metres
1 x 19 wire rope 4mm
outer sheath from 6mm Braid on braid stretched tight with heat shrink and whipping at both ends to stop it slipping ( maybe 150mm of heat shrink every 2 metres)
outer cover of 6mm pipe insulation
Last two covers only to protect sail
swaged terminals to fit Ronstan forks. 2copplane suggests Ronstan rf79 and rf75
as long as you furl in direction of lay it should remain solid.
Not sure whether it will be flexible enough to flake into bag
Any thoughts
Keith

 

[Ian_Edwards]

My 2p worth, I think 1x19 wire rope may kink when you release the tension on the halyard, even if it's furled with the lay. i think you'll find you have stored a lot of energy in the wire rope. As you know it's designed for standing rigging, it's not designed to withstand torque.

I have a top down furler on a 46ft boat and it allows me to handle a 2000 sq ft masthead asymmetric set on a carbon fiber bowsprit, single handed, so they do really tame a big sail. I had several "scares" handling the same sail with a furler on the tack, to the point were I didn't use it.

The torque rope and furler is a Karver system, and you really need to tension the halyard for it to work well, and I notice a lot of "spin" in the system when I release the halyard tension. The furled sail does pack down into a sail bag, but I have to figure of 8 the torque rope/sail.
I hope this helps.

 

[cagey]

Thanks for reply, only ever seen this kit on Internet, can't see if there is swivel at top and bottom how it can store up energy, realise your probably right cos you've got and used one.
Keith

 

[estarzinger]

Perhaps a better idea . . . . A piece of dyneema cored double braid. . . . Twice as long as necessary...... Spliced loops on both ends. . . . . .Fold in half . . . . . Sew the two half together. Leaving the end loops at the bottom and the fold loop at the top.

That will be strong, low stretch, a bit bulky to help the furl, and relatively anti-torque.

I have a furling code zero and that is essentially what I have on the luff.

 

[2copplane]

I'd never thought of wire, mainly because I didn't have any lying around, but worth a go if you have some spare.
4mm looks a bit low on swl perhaps something like this

6mm 7x19 Galvanised Steel Cable MBL 2160kgs Clear PVC Coated 8mm.

The plastic coating will help transmit the torque, and protect the sail.

I've just been sat with a length of 4mm plastic coated and it certainly seems to transmit the torque well, if wound the correct way, impressive given its diminutive diameter. My main reservation is you would have to be really careful to wind the correct way or it will b@gger the wire up.

If you are having to buy in materials then it may be less risky to buy a facnor torsion rope, which comes with thimbles for terminating. Probably circa £120.00, which is the cheapest I managed to identify.

I'm not keen on the insulation idea as it may be a little fragile and not transmit the torque, and make stowing tricker, as much more bulk and less bendy. Perhaps something to try later?

The torsional strength of a tube increases to the power 3 (?) with diameter, so the bigger the diameter of the torsional tube the better. Hence my idea to use heat shrink round the outside to act as the torsion tube. However steel is a hell of a lot stronger than a bit of heat shrink!

Please Keep me posted on progress.

Another option could be to use the wire but use pneumatic nylon tubing as the outer sheath, with wire down the centre it would be unlikely to kink,when tightly furled, or stowed.