Dyneema + Low Friction Thimbles

Since I took up sailboat ownership I discovered the level of innovation with UHMWPE has been remarkable in the sailing world. I did not know that my background in rock and alpine climbing would pave the way into utilizing the same dynamic and static systems used for fall protection. There are four factors that are almost exactly the same between climbing and sailing: weight, friction, force and mechanical advantage.

Antal Low Friction Ring
Antal Low Friction Ring
Samson Amsteel
Samson Amsteel

While mechanical advantage is generally only used in rescue scenarios and big-wall gear hauling, it is still a requirement if you plan to voluntarily or involuntarily explore these scenarios. When hauling gear and climbing ropes instead of rock, you must use a static line. When setting anchors into rock for fall protection, the system is designed to accept a static and directional load. I learned how to safely and quickly install equalized anchors using aluminum carabiners to connect the static anchors to a dynamic rope, thus reducing the shock-load on the anchor and on my fragile body. I also learned about the materials that are commonly used for static loads. The legendary Fred Beckey once shopped around used clothing stores to find silk neck ties, which would be used as the connection between the anchor carabiner and the climbing rope carabiner. They would provide the strength needed, without any sort of factory testing to prevent a fatal fall. Today we still use the same concept of a strong and static loop to connect a dynamic rope to an anchor but now are using sewn dyneema slings. They are highly abrasion resistant and stronger than any necktie ever was. The weight savings for being able to move fast and light over difficult terrain is greater than ever.

Now looking at sailing and the invent of dyneema, I am seeing a very similar change in how we look at our systems. Sailboat racing has provided the innovation, since they would rather have as little weight as possible with the strongest systems available to them within a reasonable cost. So we gain weight, strength, durability and cost advantages by choosing dyneema over 316 marine grade steel. Steel does last longer when exposed to the sun but it weighs considerably more than dyneema when comparing strengths. The verdict is still out on which would actually last longer as a structural component, exposed to the weather. Does ultraviolet radiation cause more damage than corrosion with respect to the strength of the material? The cost for steel is much, much higher than the cost for dyneema when comparing strengths. Now durability plays differently with both materials. Steel is rigid while dyneema is highly flexible. Where one may be an advantage, the other may be a disadvantage. It really depends on the situation.

The first two systems I would like to discuss are the concept of soft shackle and the concept of low-friction blocks. Both are fairly new and have sprung up as a replacement for their steel counterparts. Soft shackles are simply a spliced piece of dyneema which can be opened and closed securely but would serve the same purpose as a steel shackle. The difference is where length comes into play. A soft shackle can be made to various lengths to make the application much more custom to the task, whereas steel is manufactured to fit a single purpose. Granted, steel is made for much more custom situations, like turnbuckles and swivels. Steel can be bolted to provide a structural anchor point, whereas dyneema would not be suited for this application. Low-friction blocks are a much cheaper and modern way of providing a mechanical advantage over blocks with bearing assisted sheaves. The cost is significantly cheaper and the system is much more simple overall. There is a limit to the application, mainly because you are left to manufacture your own block system using only dyneema line and low-friction rings. The most common applications are barber haulers, fairleads and running backstays. I’ve seen some diagrams of how a low-friction ring 8:1 advantage would be setup, but few examples in real world scenarios and the result is more like 3.3:1 from what Allen has tested at L-36. People tend to be slow with trying something new and the cost of failure could be fairly catastrophic since failures are likely to be at a higher load point. A boom vang probably wouldn’t be an issue but a mainsheet block system could be disastrous.

So what does this have to do with Satori? Well, considering the relatively low cost, I will certainly be experimenting with soft shackles and low-friction block systems. I recently purchased a set of  stanchion blocks and fairleads for my spinnaker tack line so I could run it aft and control it in the cockpit. The cost was high as boat parts go and if I would have chosen the Amsteel and Antal route, building each part myself I could have saved a great deal of money. The thimbles range in cost from $12 to $30 with the average use being on the low end of the scale. Learning how to splice and tie fancy knots is nothing new to my arsenal of skills but it will take some time to memorize the steps and learn some of the best practices. Here would be my wish list for using the new system:

  • sheet attachment to stays’l, jib & spinnaker
  • running backstays
  • soft boom vang
  • jib barber hauler
  • stanchion fairleads for spinnaker tack line and furling line
  • lazy jacks
  • lifelines

Some resources: