Assignment of weighting values to the requirements for flotation 

 material has not been included in this report. The large variations in 

 the manner in which the flotation is incorporated into the design of the 

 booms precludes the establishment of weight values for flotation material 

 in general. What may be an essential flotation requirement for one boom 

 may be completely irrelevant in another design. 



COATED FABRICS 



This study is directed primarily at synthetic plastic material 

 rather than wood or metal. These synthetic materials are generally 

 composed of two parts: the woven fabric substrate or scrim and the 

 elastomer or resin coating. The capability of a particular material to 

 meet the requirements defined depends upon the type of weave, amount of 

 yarn and method of manufacturing the fabric, and the thickness and 

 method of applying the coating. 



Fabrics 



The substrate yarns used in coated fabrics must be interlaced or 

 woven into cloth. It is the techniques used in weaving the yarns that 

 provide many of the mechanical and structural features of the cloth. 



A woven cloth is composed of two sets of yarns: the warp yarns that 

 run longitudinally in the cloth and the filling yarns that cross the 

 warp yarns at a 90- degree angle and run the short direction from selvage 

 to selvage [5]. Selvage is the edge of the cloth in the direction 

 parallel to the warp yarns. Generally, in weaving cloth the warp yarns 

 are held under more tension than the filling yarns, resulting in differ- 

 ences in the strength and elongation characteristics of the fabric in 

 the warp and filling directions. 



In producing fabrics there are basically three types of weaves that 

 are used, the plain weave, the flat weave, and the twill weave. In the 

 plain weave, each warp yarn passes over one filling yarn and under the 

 next. Every other warp yarn is woven the same as is every other filling 

 yarn. The result is a cloth that is even sided; that is, the face is 

 the same as the back. Plain woven fabrics exhibit the maximum number of 

 inter lacings, or points at which one yarn passes over another. The 

 yarns in a plain weave may be either single or plied. Plied yarns are 

 those for which two or more single yarns are twisted together to form 

 one yarn. 



The flat weave fabrics are characterized by a pair of warp yarns 

 woven side by side as one, flat. The warp yarns are not plied; the 

 filling yarns may be either single or plied. Each filling yarn passes 

 over two warp yarns then under two warp yarns. The flat weave has fewer 

 inter lacings than the plain weave. Cloths woven in this manner, with 

 side-by- side yarns provide greater tearing resistance because slippage 

 occurs before rupture of the yarns (roping up). 



11 



