From the Bench to the Bath

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The test jig

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With some modification to our bench-test jig, we were able to place two blocks in opposition to each other, attach them via a closed loop of ultra low-stretch line and place the system in tension. The load-inducing mechanism was a vertical capstan Ideal anchor windlass capable of incrementally adding tension to the mix. A Dillon AP dynamometer was placed in series with the tension-creating tackle, and during each test, the load on the closed loop was closely monitored.

With the line and blocks loaded with 200 pounds of tension, we measured how much force it took to move the line in this closed loop arrangement. The peak load required to start the line moving was noted, but its value was less consistent than the load registered during the time when line movement was taking place. Therefore, we used the latter as the measure of efficiency and repeated each test five times in order to develop an accurate reading. The mean, median, and mode data were all quite close for each block, indicating that the measurements were quite consistent. The inline pull paralleled the line suspended between the blocks, and a conventional spring scale was used to measure the tension applied to move the line. Before and after each test, the spring scale’s accuracy was checked using a set of known fixed weights.

Once the efficiency testing was completed, we immersed the blocks in a heated, aerated saline bath devised to accelerate oxidation, crevice corrosion, and dissimilar metal corrosion. The weeklong dunk was taken in stride with only slight signs of galvanic interaction at points where stainless and alloy components met. Far more of an issue is likely to be the bearing abrasion from salt buildup—this is why manufacturers of composite-bearing blocks recommend rinsing off salt and windborne particulate material with fresh water between uses.

Darrell Nicholson
Practical Sailor has been independently testing and reporting on sailboats and sailing gear for more than 50 years. Supported entirely by subscribers, Practical Sailor accepts no advertising. Its independent tests are carried out by experienced sailors and marine industry professionals dedicated to providing objective evaluation and reporting about boats, gear, and the skills required to cross oceans. Practical Sailor is edited by Darrell Nicholson, a long-time liveaboard sailor and trans-Pacific cruiser who has been director of Belvoir Media Group's marine division since 2005. He holds a U.S. Coast Guard 100-ton Master license, has logged tens of thousands of miles in three oceans, and has skippered everything from pilot boats to day charter cats. His weekly blog Inside Practical Sailor offers an inside look at current research and gear tests at Practical Sailor, while his award-winning column,"Rhumb Lines," tracks boating trends and reflects upon the sailing life. He sails a Sparkman & Stephens-designed Yankee 30 out of St. Petersburg, Florida. You can reach him by email at practicalsailor@belvoir.com.