SEA-FISHERIES LABORATORY. 145 
the rope till it touches the water. The length of rope 
between the water surface and the block is then recorded, 
and from these data the depth at which the net is towing 
is easily calculated: 
Total length of rope out* _ length of rope above water , 
depth of net height of davit head =’ 
assuming’, of course, that the line is straight ; and with a 
thin wire rope, and the comparatively heavy strain of 
hauling the net with its shear-board, the deviation from 
the straight may be neglected. 
*<'The metre wheel is read when the net is first in the w ater, and 
then again when the haul begins. 
