Manual of military engineering . f water, viz., 62| lbs. The actual flotation then of the log given below, if it werepine, would be :— 95 X (62J - 40)or 95 X 22^ = 2,137i lbs. As, however, timber absorbs a great deal of water, only | ofthe above can be safely relied upon. This available buoyancy will then be—I X 2J37| = 1,781 lbs. 272. The contents in cubic feet of an unsquared log of timbercan be found by the following rule :— L ^ (D- + Dd + d-). Where L = length of log- in feet,D, d = diameter at ends. Thus, if the log- is 3 feet and 2 feet in diameter at the endsand 20 feet Ion or— Bridges
Manual of military engineering . f water, viz., 62| lbs. The actual flotation then of the log given below, if it werepine, would be :— 95 X (62J - 40)or 95 X 22^ = 2,137i lbs. As, however, timber absorbs a great deal of water, only | ofthe above can be safely relied upon. This available buoyancy will then be—I X 2J37| = 1,781 lbs. 272. The contents in cubic feet of an unsquared log of timbercan be found by the following rule :— L ^ (D- + Dd + d-). Where L = length of log- in feet,D, d = diameter at ends. Thus, if the log- is 3 feet and 2 feet in diameter at the endsand 20 feet Ion or— Bridges ofrafts oftimber. the cubic contents = 2095 W^eightof 273. The follow ving are approximately the w imber. foot of different kinds of timber :— Ash, English .. 46 lbs. Pine .. Beech .. .. 43 „ Poplar Chestnut .. 41 „ Sycamore Elm ., 37 ,, Teak, Indian Fir .. 33 ,. „ African Larch .. .. 33 „ Yew .. Maple .. .. 32 „ Walnut Oak, English .. 57 „ Blue Gum Willow .. .. 25 lbs. 40 lbs. 365161413863 M Jlate Opposi te. jjcLtye 70. 107 CHAPTER XIX.—BLOCKS AND TACKLES—USE OF SPARS. 274. Blocks are used for the purpose of changing the direction Blocksof ropes or of gaining power. and They are called single, double, treble, &c., according to the of sheaves, which are of metal or hard wood, andrevolve on the pin, which should be kept well lubricated. Snatch blocks, Fig. 1, PI. 73, are single blocks with anopening in the shell and strap on one side, to admit a ropewithout passing its end through. The rope with which tackles are rove is called a fall. Tooverhaul is to separate the blocks. To round in is to bring themcloser together. When brought together the blocks are saidto be chock. 275. A tackle is rove by two men, back to back, 6 feet apart; blocks should be on their sides between the mens feet,hooks to their fronts, and the coil of rope to the right of theblock at which there are to be the greater number of wi
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