CHAPTER XII.
Cordage. How Preserved. Strength. Blocks and Tackle. Knots, Hitches, etc. Lashings.
Bridges, Trestles, Piers, etc. Single-sling and Treble-sling Bridges. Stringer Bridges. Fords. Flying and Floating Bridges. Rafts and Casks.
CORDAGE.
Ropes are distinguished as to size by their circumference in inches. Their length is given in fathoms.
Hemp rope when new stretches freely, and deteriorates very much after a few months' wear. It is about one third stronger than manilla rope.
To ascertain the strain in pounds a rope will bear without breaking, square the circumference and multiply the result by the tabular unit in the following table:
| Kind. | Circumference. | White. | Tarred. | ||
| 3-strand. | 4-strand. | 3-strand. | 4-strand. | ||
| Hemp | 2.5 to 6 in. | 1140 | 1330 | 850 | 1000 |
| 6 " 8 " | 1090 | 1360 | 825 | 940 | |
| Manilla | 2.5 to 6 in. | 810 | 950 | .... | .... |
| 6 " 12 " | 760 | 835 | .... | .... | |
For ropes in daily use reduce the tabular unit one third to meet reduction in strength by wear and exposure.