Pull it Until it Breaks

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hydraulic ram

All testing was carried out at an approved test facility in Newcastle, Australia: J.L. Robertsons, which is adjacent to one of Australias large coal-mining areas. The test rig is used to certify lifting components for the local mining industry on a daily basis. The facility can test up to 95 tons, far more than we require. This is the same facility where we tested all of our anchor chains. (See PS June 2014, November 2014, January 2015, and March 2015 online.)

The rig is fairly simple. A ram loads the components, and a load cell tracks the increasing load versus deformation. One of each shackle was tested in exactly the same way, one after the other. Testing just one unit, as we did, is of limited statistical value, but we will be testing more units in the future.

Two notes about safety factors and ratings. A safety factor, as we described in our previous study of chains (see PS June 2014 online), is the ratio between what would be considered the safe working load limit (SWL or WLL) and the minimum tensile stress (MTS), also called minimum break stress (MBS). MTS is the minimum point at which a shackle or link can be expected to fail. It is mathematically derived, based on the type of steel and structural dimensions; WLL is a fraction of MTS. Ultimate tensile strength (UTS) is the breaking point based on actual data, and manufacturers are supposed to batch test to ensure UTS is higher than MTS. Finally, there is proof test, which is two times the working load limit and should result in no deformation. Crosby, Campbell, and Peerless proof test every shackle they make.

When assembling an anchor rode, use the working load limits for matching shackles and chain, but be aware of the different safety factor being applied. The safety factors for the shackles we tested range from 4.5:1 to 6:1; so a shackle with a slightly lower working load limit might actually be the stronger one. To further confuse the issue, some shackles are rated in metric tons, others in imperial or short tons-even when the sizes are advertised in inches.

Practical Sailor has been independently testing and reporting on marine products for serious sailors for more than 45 years. Supported entirely by subscribers, Practical Sailor accepts no advertising or any form of compensation from manufacturers whose products we test. Testing is carried out by a team of experts from a wide range of fields including marine electronics, marine safety, marine surveying, sailboat rigging, sailmaking, engineering, ocean sailing, sailboat racing, and sailboat construction and design. This diversity of expertise allows us to carry out in-depth, objective evaluation of virtually every product available to serious sailors. Practical Sailor is edited by Darrell Nicholson, a long-time liveaboard sailor and trans-Pacific cruiser with more than three decades of experience as a marine writer, photographer, boat captain, and product tester. Before taking on the editor’s position at Practical Sailor, Darrell was the editor of Offshore magazine, a boating-lifestyle magazine serving the New England area. Darrell has won multiple awards from Boating Writer’s International, including the Monk Farnham award for editorial excellence. He holds a U.S. Coast Guard 100-ton Master license and has worked as a harbor pilot and skippered a variety of commercial charter boats.

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