dyed cloth in case of the coated sailcloth the permeability to air goes down to zero with the coating amount being considerably lower for the calendered cloth a lower amount of coating enables the weight of the finished sail to be reduced and such a saving in weight can be utilized to apply reinforcing measures reinforcing yarns with a view to achieving optimum results the treatment by means of the corrugated roll must always be performed on both sides examination series carried out on a polyamide gray cloth processed by means of a cross corrugation roll with 20 lines mm at a temperature of 200 u00b0 c have shown a significant interdependency between air permeability and pressure with an optimum at 200 to 400 n mm 2 the gray cloth had been calendered on both sides with dyed cloth the permeability at 300 to 400 n mm 2 was found to be 10 to 20 l dm 2 for the purpose of determining the resistance to air sail membrane samples were tested in a wind tunnel using an mav scales test piece 6 component strain gauge mav scales at a windspeed of 18 m s the mav scales test piece was a trapezoidal wing of small extension having a symmetrical profile the leading edge sweep was 36 u00b0 the rear edge was straight the wing area was covered with the cloth patterns in such a manner that the covering embraced the top side of the wing completely while just abt a quarter of the bottom side was covered for a non corrugated sail membrane the measuring results showed a coefficient of drag value c wa of 7 08 u00d7 10 u2212 3 on average for a membrane.