56 HYDROGRAPHICAL SURVEYmG [chap. i. 



flusli, and the ])lanks above and below are screwed to the 

 heads, the })()k^ })assing through the centre of each plank by 

 a hole cut for the purpose. The planks can be hollowed out 

 to fit the heads of the casks for further security. 



Three casks can also be used if only small ones are available, 

 by fitting the planks in triangle, with another plank across, 

 through which the pole passes. 



The strop for weighing should be of wire, wliich keeps well 

 open from its own stiffness, and facilitates hooking on for 

 hoisting in. 



A slip by which the cable is attached to the mooring span 

 assists in weighing the beacon. 



Use a small kedge and light chain for anchoring, except in 

 water, say, over 60 fathoms deep, when hemp or wire rope 

 should be employed, with some chain next to the anchor to 

 take chafe. Hemp is apt to chafe through, even though the 

 precaution of " keckling " it may have been adopted. Its 

 use, therefore, should be avoided unless the depth renders it 

 necessary. 



Beacons have been anchored in 3,000 fathoms by means of 

 sounding wdre, and weight of 100 pounds. 



In water of from 20 to 100 fathoms, about li times the 

 depth is necessary for the length of mooring rope. In deeper 

 water, less. 



This beacon will float nearly upright, and will carry in 

 moderate weather a flag 12 feet square, of calico, wliich is 

 lighter than bunting, and A^dll be visible from the ship 10 miles, 

 with a 30-foot bamboo. Black, with other colours to distin- 

 guish one beacon from another, is recommended. 



A piece of signal line should be fitted along the luff enclosed 

 in several folds of the calico, and the flag is stopped to the 

 bamboo round this. 



Another form of cask beacon is made by woulding three 

 casks to the central spar with rope, which tautens when wet, 

 but the beacon above described is more quickly fitted when 

 the parts are ready beforehand. 



Slipping a beacon is best accomplished from the mainyard, 

 but the foreyard can be used. The anchor being over on the 

 weather side, and beacon lowered into the water, slip by means 

 of a large well-greased toggle, as the moorings tauten. 



