The fibers on the outside carry more load than those on the inside, which may actually be slack, doing no work at all. Strength by TypeĪny rope is weakened when loaded around a small radius. The previous topping lift showed very little wear after for 15 years without any sleeve or thimble. Even without a sleeve it should last for a long time. The topping lift on one of our test boats attached to a relatively sharp-edged shackle, so we used a webbing sleeve for padding instead of a thimble. But what about eyes attached to polished stainless shackles? Unless they are under extreme load and simultaneously sawing back-and-forth across the shackle pin, ring, or other load-bearing attachment point, there will be virtually no apparent wear.Ĭhafe can vary greatly depending on use. Abrasion is aggressive, and a nice thick layer of steel offers the best protection. A mooring line around a rusty shackle is a perfect case for a thimble. Some general considerations our testers explored: Which is better for typical applications on a racing keelboat or cruiser? The load-bearing surfaces of the spliced eye can also be protected with a secondary cover or tubular-webbing chafe guard (See Fiber Coating Protection Plan, September 2015). Thimbles come in many types, including wire-rope thimbles, closed, or sailmakers thimbles, and captive-rope thimbles of many designs.Ī thimble isn’t the only means of guarding against chafe. We’ve seen similar near failures resulting from open-style thimbles in mooring applications as well. A closed thimble or a webbing sleeve is a safer choices for this application. Had it failed, the consequences would have been serious. We were sent images of a bridle on a Jordan Series Drogue (a drag device used to slow the boat in a storm), and the bridle was severely chafed by a thimble that shifted. Any side load or binding could allow the thimble to shift its position. As a result of all the stretch, even factory-installed thimbles become loose at high load.Įven when a thimble is very well-fitted and tightly seized-as good and any we have seen-and stretched to the normal working load (10 percent breaking strength), it becomes quite loose. Because each leg of the eye carries only half of the load, the stretch at 20 percent of breaking strength should be only 6 percent, but we must add to that some construction stretch, since it takes time for a splice to settle in. Nylon double braid rope stretches about 12 percent for every 20 percent of breaking strength 3-strand rope stretches about 15 percent and climbing ropes stretch about 18 percent. Cheap wire thimbles often have sharp edges, and even well-polished examples can open the weave or chafe at strands, or seriously damage a splice if they shift.Īt the heart of the problem is stretch. But are thimbles best, and is a thimble best or even required in all circumstances? We are especially interested in strength.Ī light thimble can distort under high load. And the thimble also increases the turning radius, which more evenly distributes the load among the fibers that make up the weave. Undoubtedly, a thick layer of steel provides the ultimate in abrasion resistance when attaching to a rusty, galvanized mooring shackle. A great many sailors believe a splice intended for high loads is not complete until it is fitted with a thimble.
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