pilot cloth

Most likely because its archetypal use was in making pilot jackets for pilots (helmsmen) and pilots (assistants to helmsmen).

pilot cloth (countable and uncountable, plural pilot cloths)

1. A coarse, stout kind of cloth for overcoats.

   Hypernyms: cloth, fabric, textile, material (fabric sense) < material (matter sense), matter, stuff

   Coordinate terms: duckcloth, waxed cotton, cotton wax, tarpaulin

   • 1851 November 14, Herman Melville, “The pulpit”, in Moby-Dick; or, The Whale, 1st American edition, New York, N.Y.: Harper & Brothers; London: Richard Bentley, →OCLC:

     I had not been seated very long ere a man of a certain venerable robustness entered; immediately as the storm-pelted door flew back upon admitting him, a quick regardful eyeing of him by all the congregation, sufficiently attested that this fine old man was the chaplain. Yes, it was the famous Father Mapple, so called by the whalemen, among whom he was a very great favorite. He had been a sailor and a harpooneer in his youth, but for many years past had dedicated his life to the ministry. At the time I now write of, Father Mapple was in the hardy winter of a healthy old age; that sort of old age which seems merging into a second flowering youth, for among all the fissures of his wrinkles, there shone certain mild gleams of a newly developing bloom—the spring verdure peeping forth even beneath February’s snow. No one having previously heard his history, could for the first time behold Father Mapple without the utmost interest, because there were certain engrafted clerical peculiarities about him, imputable to that adventurous maritime life he had led. When he entered I observed that he carried no umbrella, and certainly had not come in his carriage, for his tarpaulin hat ran down with melting sleet, and his great pilot cloth jacket seemed almost to drag him to the floor with the weight of the water it had absorbed. However, hat and coat and overshoes were one by one removed, and hung up in a little space in an adjacent corner; when, arrayed in a decent suit, he quietly approached the pulpit.