Critical items that exert large sheer forces (forces that are roughly parallel to the substrate that the hardware is bolted to), such as chain plates and mooring cleats, should be installed in thick, solid fiberglass, and the force must be well-distributed to the surrounding structure. It is important to note that our testing looked only at compression and tension. For details on the test protocol, see the accompanying How We Tested. The data from our tests is summarized in the accompanying tables. We wanted to do this without significant distortion or damage to our sample decks fiberglass skins or its balsa core.įor a plate to meet our criteria, the bolt had to fail before the plate. Our aim was to find materials that can reach the proof strength of the 1/4-inch bolt (1,950 pounds) that we were bolting. We also made sample backing plates with a few layers of 17-ounce biaxial cloth laminated against the inner skin, and we made samples with FRP plates bonded to the inner skin for increased strength. Although some of these materials are clearly a poor choice for backing plates, people still use them, so we included them in testing. During testing we compared American standard bolting washers and fender washers and several common backing-plate materials, including 1/8-inch aluminum, 3/16-inch and 1/4-inch fiberglass (FRP) plate, 1/8-inch stainless steel, 1/2-inch plywood, 3/4-inch teak, and 1/2-inch Starboard (HDPE). Our deck sample for testing was a balsa-cored, half-inch-thick fiberglass that precisely replicated that of PS tester Drew Fryes 32-foot PDQ catamaran. For this report, we looked at existing practices and compared them with what we found through empirical testing. Now that weve determined that some materials are better than others for backing plates, we sought to find guidance on the minimum dimensions for a backing plate for load-bearing hardware. In this issue, we take our investigation one step further. Anyone who has replaced or re-bedded his mainsheet traveler, genoa track, stanchion, winch, or similar deck hardware has probably noticed that the washers used to spread the load on the underside of a balsa-core deck are often bent and mis-shaped, apparently too small to the spread the load. We also tested several materials used to make backing plates when attaching fittings, hardware, and structural components to the boat.īacking plates, often paired with topping plates, play a critical role in spreading load across the substrate to which hardware is bolted. Practical Sailor recently tested the strength of solid laminate with relation to the bolt passing through it (see PS, June 2016 online). How big of a backing plate do you need for your new winch? Genoa track? How about for your keel bolts? What is the best material? The best design?
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