THE SHIP AND ITS EQUIPMENT 



43 



towed at a good speed to keep the boards in position, and the 



vessel skilfully steered, so that the lines 



must necessarily be towed from the stern. 



It was found very difficult, however, to 



adopt this plan to our requirements, the 



chief drawback being that everything must 



be of the very strongest materials. Sir 



William Thomson long ago, when working 



at his sounding machine, discovered that 



the drums were easily burst, and the 



trawlers too have had similar experiences, 



in spite of their using drums of cast metal 



several inches thick. 



The " Michael Sars " could not, of 

 course, use such large appliances, for if in 

 addition to overcoming the resistance of 

 two ponderous otter boards, 6 feet by lo 

 feet, she had to tow a pair of wires each 

 many thousands of metres long, she could 

 obviously not have got over much ground ; 

 and besides, it would have been next to 

 impossible to prevent such long lines from 

 fouling one another. We were compelled 

 therefore to trust to a smaller size of trawl, 

 and to substitute a single warp, from the 

 end of which we led a connecting line, 50 

 fathoms in length, to either otter board 

 (see Fig. 26, line and bridle). A similar 

 arrangement for small otter trawls had 

 been already successfully tried by C. G. 

 Joh. Petersen. During previous cruises of 

 the " Michael Sars " we had operated a 

 trawl with 50 feet of headrope at a depth 

 of 1830 metres, and during our Atlantic 

 expedition we succeeded in working the 

 same appliance at a depth of 5160 metres. 

 Our success must be ascribed to the solid 

 construction of our gear. The drum of 

 the winch which took the 9000 metres of 

 wire was of the best cast steel, and the 

 blocks were made as substantial as pos- 

 sible, though even then they had to be 

 changed during the cruise, because 



Fig. 25. — Deck Arrange- 



the MENTS OF A TRAWLER. 



