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The weak link in the rigging design, as delivered from the factory, is the choice of bolts that hold the chainplates to the bulkheads and knees. Bruce Rankin published an engineering analysis in the March 1992 Mainsheet and this is reprinted in the Maintenance Manual. I won't repeat the analysis here, but I will repeat the recommendation. Increase the number of bolts from three to six or increase the size from quarter-inch to five-sixteenths-inch. Either will double the strength of the fastenings. Add backing plates behind the plywood. We usually use quarter-inch by 1 inch by 6 inch long or so, in aluminum. Stainless would be better, but is impossible to drill in place. Note also that these bolts should not be threaded down the full length of the bolt. Where the bolt passes through the chainplate, the metal should be full-diameter. This is called a shoulder bolt.
Gordon Laco provides good free advice and entertainment on the Public List 
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