THE OTTER TRAWL 303 



moves forward obliquely to the direction of tow. 

 The two boards in this way keep a strain on the head 

 line and ground rope, which increases with the speed 

 at which the vessel is towing. It is probable that under 

 normal working conditions the distance which the boards 

 actually keep apart is about two-thirds the length of 

 the head line of the trawl. The head line being floated 

 with cork, rises up in an arch between the two boards, 

 and gives a much higher opening to the mouth of the net 

 than is yielded by the beam trawl, in which the height 

 of the opening is fixed by the height of the beam above 

 the ground. This increase in the height of the opening 

 of the mouth of the net constitutes one of the chief 

 advantages of the otter trawl as a fishing instrument, 

 since the take of round fishes, which swim a little above 

 the actual bottom, is thereby much increased. 



The size of the otter trawl usually worked on a steam 

 trawler is as follows : 



Length of head line, 86 feet. Length of ground rope, 

 125 feet. Dimensions of otter boards : length, 8 feet ; 

 height, 4 feet 3 inches ; thickness, 2j inches. Size 

 of mesh, measured diagonally with mesh taut, diminishes 

 from 5^ inches in the square to 2| inches at cod end. 



The fine-meshed nets already mentioned in connec- 

 tion with beam trawling may also be fitted to otter 

 trawls. 



On a commercial steam trawler two independent 

 towing warps are used, one for each otter board, and 

 special iron gallows are fixed to the vessel's side, fore 

 and aft, for getting in the heavy boards. It is not 

 necessary to give here the details of the method of 

 shooting and hauling these heavy trawls, as this should 

 not be attempted excepting with a specially fitted 

 vessel and under expert direction. 



The following instructions r may be useful for working 



