The 'A' class model yacht racing rule devised in 1923 is described and its parallels with their full size metre class rules are discussed. Unlike their full size counterparts, successful model yachts from all decades of the rule's existence survive in good condition. This provides an opportunity to assess progress in yacht design using towing tank techniques. Six championship winning models, representative of typical design types, were tested in the towing tank and the results are presented Windward sailing performance prediction calculations for the models are also using representative soft sail force coefficients. The developments in hull design, sail materials and hull construction leading to the latest 'A' class models are described. The use of model sailing trials as an aid to the design of full size yachts is also discussed.

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