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S&S Swan General - Synthetic rigging for Swan 40
09 March 2019 - 09:43
Join Date: 03 March 2007
Posts: 241

Synthetic rigging for Swan 40

Dear all,


I am considering going from Stainless wire to Dyneema standing rigging.  I am looking at Dyneema Dux  (heat treated dyneema) with Bluewave terminals.. I am considering changing the shrouds both inner and outer as well as the backstay. 

Reasons for doing so are weight in the rig...ease of repair at sea.. I also get rid of the back stay insulators and can run the antena inside the Dyneema... 

I also like the idea that I can replace a shroud at sea without specialist gear!! I plan to carry an extra 20 M of Dyneema just in case.


Q to the Professor. What loads are on the shrouds and backstay on our boat ?? see this site. I am considering 11mm but is this sufficient? or should I go to 13mm..



Has anyone done this conversion??


Fair winds


Mike from Stormsvale




11 March 2019 - 10:33
Join Date: 02 January 2008
Posts: 1547

Dear Mike

There are two basic requirements to look at when replacing standing rigging - strength and stiffness. The present wire rigging can be used as reference when evaluating these properties.
The Dux information suggests that SWL (Safe Working Load) is 20% of the breaking strength, can be noted here that this percentage refers for fiber ropes generally. The SWL for wire is higher, 30% is often quoted, this would require Dux to have at least 1.5 times higher breaking strength, but as the Bluewave terminals bend the rope over a very small radius, more would be preferable. We will see later, however,  that this strength requirement is insignificant.
For comparing the stiffness the Dux elastic modulus would be required, have not found such numbers, but Colligo Marine (a supplier of this rigging) gives some stretch numbers and the conclusion is that stretch is 2.5 times over that for 1x19 wire. 
This means the cross section needs to be that much bigger for the same stiffness, and the strength will then also be 2.5 times more, i.e. over the strength requirement suggsted above. 
The Dux diameter needs to be 1.6 times the wire diameter, and the weight is 38% of the wire weight. 
Creep also needs to be mentioned, Colligo Marine presents a diagram with the expected creep per year at a fairly low tension. Normal shroud pre-tension would cause about twice the mentioned amount of creep, while sailing doubles that again to four times.
Example: if we look at your main shroud, about 15 m long, the creep due to pre-tension would be 5 mm per year, and double that amount during sailing, usually a fairly short time span. This amount of creep can be compensated for by tightening the shrouds, and when there is no adjustment left, by doing new slightly shorter splices.
Stays do not need to be pre-tensioned except for when sailing on the wind, but the sailing loads may be higher. 
Pls note that Colligo also offers terminals with larger radius for the rope.
Would you have questions?
Kind regards


12 March 2019 - 18:12
Join Date: 01 April 2007
Posts: 106

Dear Mike and Professor,

I found some interesting information on That information is from the owner of Swan 48 Isbjorn. He says:

Creep, unlike stretch, which is an elastic deformation from which a material “rebounds,” is the permanent elongation of fibres over time under load. Like pulling taffy, Dux fibres that have crept will not rebound. If sized incorrectly, a Dux rig will eventually go slack under its pre-tensioned load.

Therefore, to size Dux correctly, the key is to determine the typical pre-tension load carried by the rig. Then, rather than a strength chart, consult a creep chart, and choose the diameter of Dux that will not creep at that load.

Again, strength is inherent—you’re inevitably going to end up with rigging that is far stronger than the wire it replaces. As a real-world example, Arcturus’ wire rig called for ¼” (6 mm) shrouds. Her Dux rig calls for 9 mm (3/8″) shrouds—that’s a breaking strength of 7,300 lbs (3311 kgs) for wire versus 26,400 lbs (11,975 kgs) for Dux.

So far (part of an bigger article)

I cannot judge if the information is correct. I will leave that to the professor, but perhaps it can add to the discussion on this forum.

I think Morganscloud is a very interesting site that offers lots of information. 

kind regards,

jan, swan 38 yulunga

14 March 2019 - 06:54
Join Date: 03 March 2007
Posts: 241

Dear Both,


thanks for the input. I have contacted Colligo and discussed the rigging. They suggested 15 mm Dyneema dux. I have decided on the Professors advice to go 16 mm and use the larger diameter Colligo fittings.. This job will start after this season and I will let you know how it turns out! 


Thanks again



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