Reefing was tried extensively during the late 80s Worrell-1000 races. It does not work because catamarans do not have backstays, instead they rely on the downhaul to bend (depower) the mast. [There were some attempts at running backstays but it did not really work] When the sail only goes partway up the mast, it cannot adequately use the downhaul successfuly and therefore the sail is over-full. Despite the lower height and smaller size, the full power makes it no better or perhaps worse than a well flattened full sail. This is why I was thinking about a cut-down sail that was specifically cut flat and still had full control of the de-powering characteristics. Of course, such a sail would need to be selected on shore and therefore only suitable for inshore buoy racing.