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Standard Rigging: the Polyethylene alternative - Article by Chris Kinzel © 2006

Published in (New Zealand) / Features, March 2006

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When Christopher Kinzel began building the rig for his 19m sailing catamaran, he wanted a lighter, cheaper alternative to conventional steel rigging. He settled for high-density polyethylene (HDPE) rope and, so far, it's worked a treat.

I first stumbled across the rope - Dynex 75 - at a fishing port near Nelson, where it is sold by an Icelandic rope and net manufacturer - Hampidjan. It's reported to have half again the breaking strength of steel of the same diameter. How much does it stretch? It doesn't, they said. Could it be used for standing rigging?

My research expanded to other rope manufacturers, mast builders, riggers, engineers, composite rigging builders, sailmakers and ocean racers - and I received a mixed response: "... wouldn't use it for the danger of chaffe ... sure, we use it all the time ... the stuff creeps ... good for rotating rigs, but not a fixed rig like yours ... to avoid creep you've got to over-spec it and you'll be fine..."

The rope, I could see, offered a number of potential advantages. Costs for rope vs wire were about the same, although fittings would be cheaper and the weight savings would be huge. The creep issue seemed avoidable, albeit difficult to monitor, and there would be an improved safety margin. Termination and tensioning were design issues I would enjoy solving. The installation would be a bit time consuming, but I could do it myself. I decided to use it.

So what is HDPE? The base material is Ultra High Molecular Weight Polyethylene, refined by Netherlands company DSM and marketed as Dyneema. Its characteristics are well documented, and it is sold to rope makers, sail makers and fabric makers worldwide. Hampidjan braids the material (12-braid) and adds a secondary heating/tensioning treatment - a UV protective and abrasion resistance coating - and markets it as Dynex 75.

The rope, says Hampidjan, was developed as a replacement for steel when trawling, towing, and mooring large objects. The company has carried out plenty of testing and comparisons with respect to tenacity vs elongation, specific strength vs specific modulus, creep, bending fatigue, abrasion, and UV resistance. It is the only Dyneema braider (of many), which is Lloyds certified.

Selecting the diameter

Our vessel - Augustina - makes its rig work. The loads are as follows: six tonnes at the cap shrouds when flying a hull, 10 tons when you pitchpole.
If breaking strength was the only consideration, we could use a smaller diameter than a comparable 1x19 wire cable. However, the Achilles heel of HDPE seems to be cold creep: permanent deformation from a continuous load, measured over time (months and years) at a given temperature.

Hampidjan has test data showing that a rope put under a continuous load of 50 percent of its minimum breaking strength at 20oC will creep beyond 10 percent after seven months; not a very useful length of time for holding up a mast.

However, when the sustained loads are at 20 percent of the minimum breaking strength at 20oC for a year, 0.5 percent creep is encountered. A drop in temperature 10oC will improve this period by a factor of three or four. Easing shroud tension when not in use for extended periods can also help.

For Augustina, riggers and mast builders said I could get away with 12mm 1x19 SS wire, but recommended 14mm cap shrouds. For the rope alternative, I chose 16mm Dynex 75. This was based on the predicted maximum sustained load while flying a hull (six tonnes) - some 23 percent of the minimum breaking strength for the rope.

After three years of flying a hull in 20oC, we might see 1.5 percent creep (according to the charts). That would give us a useful life of 18 years of hull flying until we reached the 10 percent elongation limit. We've been sailing about three months and have yet to sustain flying a hull, so I'm guessing creep won't be an issue.

In terms of weight savings, the approximate difference between the rope and the SS cable I would have used is:

* 125m x 16mm Dynex = 20kg
* 110m x 14mm SS wire = 106kg
* That's a weight saving of 86kg (or a factor of 5.25)

In an ultimate dynamic loading situation (diagonal pitchpole) when relying on the minimum breaking strength of a shroud, the safety factor difference is:

* 14mm SS wire = 1.4 * 16mm Dynex 75 = 2.8

Termination design

The race is on among designers to come up with end fittings that accommodate a pin connection for the rope. Some have tried the various wire end styles such as swageing, cone inserts and cold casting - without success.

Instead, I have found three styles for eye-splicing 12-braid line. The weaving goes quite fast once you get into it, and it can be undone and repositioned. The braid is loose enough to work without tools, though the proper size tubular fid makes the job easy. Thanks to the UV protective coating the fibers maintain their bundles well.

The simpler Brummel style takes minutes while the slightly stronger Tuck style can take about an hour. Add at least another hour if you want a tapered finish (it offers the maximum strength and elegance).

Eye splicing will reduce a line's minimum breaking strength by 5-10 percent, while a simple bowline knot will reduce it by 20-30 percent. A description of the Brummel and Tuck styles can be found on Hampidjan's web site (

Augustina's cap shrouds run continuous from the hounds to the chain plates and back up to the upper spreader bases. The spreader tips are locked up and down by the diamonds, which run in reinforced plastic hose over a molded groove.

The upper ends of the reverse diagonals are spliced into the cap shroud just above the spreader tips. In fact, the upper diamond was added after the mast went up when we wanted more forward push (mast camber); no need to call a crane or a swaging guy or machine shop.

Dynex 1


The rig was standing but the tensioning system needed improving. A major find was Precourt Systems, a Canadian outfit working specifically on developing fittings for synthetic rigging (see It CNC-machines 6061 T6 anodised aluminum into a range of deadeyes and thimbles that accommodate various stay sizes.

Individual holes prevent the lanyard parts from binding. Following the perimeter of the shape with the lanyard hole pattern keeps the deadeye pointing in the desired direction (non-capsizing), balancing the load on the lanyard parts. The machining, styling and finish is smart, and the price very reasonable.

In our case, the nine-part lanyard (8mm Dynex, which amounts to a minimum breaking strength of 60 tons) is led with snatch blocks to a winch. While tension is applied, a bit of prying on the parts with a large screwdriver and fingers helps even up the load. Then with the sails up it's easy to tack back and forth working the slack out of the leeward side.

The lanyard starts by splicing to the lower deadeye, and the tail finishes at the upper deadeye by wrapping diagonally over the splice twice, and rolling hitches (at least four) around all nine parts. Under full tension there is enough advantage and friction in the lanyard to untie the hitches and still maintain the tension by hand (the hitches don't have to work hard).

The next improvement was to install a turnbuckle in series with ... the deadeye lanyards being the gross adjustment and the turnbuckle doing the final tensioning. This has proved satisfactory for keeping the mast in column, but we have never managed to get the headstay very straight. That may be a function of the lack of a backstay and flex in the boat.

The Dyneema fibre does not stretch, but as a braided rope it gets longer when loaded. To date, this has been the most important issue regarding Dynex 75 as standing rigging. We have tightened and re-tightened the shrouds, the mast has stayed up, and now stays straight athwartships and keeps a nice forward camber.

Measuring for length and splicing was done while the mast was horizontal. We started out with a 60cm gap between deadeyes and are now down to about half that. It's been about a season of sailing and indeed the tension seems to be stabilising. When we jump around in waves there appears to be some give as the loads spike, which I believe is good to relieve stress. However, that give must be recoiling as I'm not having to continuously tighten the shrouds anymore.

The good news is that Hampidjan has recently produced the next generation of Dyneema based rope; called Dynex Dux. Through further heating under tension the 12-braided line is pre-stretched and firmer or more compacted, is spliceable just the same and is stronger than the Dynex 75 by up to 40 percent.


Yes, replacing stainless wire with high-strength rope is possible, but not in all cases. The potential for chaffe from hanks or furler gear would seem to rule out using it for headstays.

In rigs such as multihulls with rotating wing masts, and traditional sailing vessels some rigging stretch is acceptable and a welcome relief for spike loads on the hull structure. Dynex 75 clearly offers a good improvement over wire for those rigs.

For monohulls with short staying bases that require high shroud tension to keep the mast straight, Dynex Dux will work as long as the continuous loads are less than 20 percent of the minimum break strength. The bottom line is slightly more windage for less cost, and much less weight aloft.

As for longevity, the trawlers are replacing their lines (UV protective coated but uncovered) after five years of hard service. I imagine that typical sailing rigs work a lot less. If sized and covered properly strong rope should easily out last stainless wire or rod as fatigue is no issue. With time we hope to do further testing, know more, and will keep you posted.

Chris Kinzel © 2006

SV Augustina Specifications

LOA: 19m
Beam: 9m
Displ. Loaded: 11 t
Mast height off water: 27m
Rig style: fixed D section, double sweptback 30 spreaders (lowers almost full width of vessel) Capshroud load
Flying a hull full sail: 6t
Flying a hull reefed: 8t
Diagonal pitchpole: 10t