The paper describes the test results from two sets of wind tunnel experiments carried out on a "crab claw" type sail. The unique aerodynamic and structural behaviour of the crab claw sail and spars are discussed with respect to their suitability for use in a collapsible sail system. The tests were initially aimed at the leisure cruising market as part of the "zero yacht" concept hybrid yacht. The particular challenges of configuring a boat for this market are discussed. Finally the applications for commercial sail assistance are described along with the results of a study carried out for Wallenius & Willemsen under the auspices of their "Orcelle Fund" award. This study shows in very broad terms the scope for fuel saving through the use of sail assistance. The paper also highlights how the fundamental physics of ship powering and aerodynamic behaviour relate to the process of adapting aerodynamic thrust devices to commercial ships.
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