Rope Specimens 



A heavy growth of slime bacteria was present on the surface of nylon, 

 polypropylene, cotton, and Manila ropes (Figure B-12). The fibers of cotton rope 

 were decayed considerably by bacterial action. The cotton fibers were easily pulled 

 apart by tweezers or one's fingers. Because of the damaged fibers, considerable 

 difficulty was experienced attempting to place a splice at each end of the cotton 

 rope for a breaking-strength test (Figure B-13). Only a few marine borers were found 

 on the cotton, resulting in little damage to the fibers by borers. 



Manila rope specimens were severely damaged by marine borers. The fibers 

 were severed completely by the boring action of small borers. The l/2-inch-diameter 

 Manila rope was so heavily Infested with borers deep inside the rope that it was 

 impossible to count the numbers present. It was estimated that there were several 

 hundred per lineal inch of the entire length of two 5-foot rope specimens (Figure B-14). 

 In addition to the borers, slime bacteria were responsible for the decay of fiber 

 materials. 



A splice could not be placed on the Manila rope specimen for a breaking- 

 strength test because of the deteriorated condition of the rope. However, by examining 

 the damage to the hemp fibers. It was estimated that 75 percent of the tensile strength 

 of the rope was destroyed. The deterioration of fishing nets and ropes made of natural 

 fibers has always been a serious problem. It has been recognized that microorganisms 

 are the primary cause of decay of fibers, resulting In loss of tensile strength. The 

 microorganisms responsible are chiefly cellulose-decomposing bacteria. 



Examination of the nylon and polypropylene ropes under a microscope showed 

 that the fibers of these ropes were not decayed by microorganisms or severed by 

 marine borers. On the contrary, the fibers were in excellent condition. Table III 

 compares the breaking-strength tests of the exposed rope specimens with that of 

 unexposed specimens. 



Plastic Specimens 



The 3-foot-long solid plastic rods and flexible tubes after 6 months of exposure 

 are shown In Figure B-15. Plastics not deteriorated by marine organisms are noted 

 later under the heading Unaffected Materials. 



Cellulose Acetate Rod . Ten borers had penetrated Into the solid plastic along 

 the edge of the plastic electrical tape wrapping. The depth of penetration was about 

 1/64 Inch, and the diameter of the largest borer hole was about 1/32 Inch. A few 

 borers had also penetrated slightly Into the smooth and roughened areas of the rod. 



Polystyrene Rod. About 25 borers were found boring Into the solid plastic 

 along the edge of the tape wrapping. The highest concentration of borer holes was 

 found on the lower 2-1/2 inches of the smooth area of the rod exposed near the 

 sediment. Approximately 100 small borer holes In a 1 -square-inch area were found. 

 In addition, a few borers were also present on other exposed areas of the plastic. 



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