THE TECHNIQ^UE OF TRAWLING 



117 



Wind and current have caused 

 trouble; the trawl has come up ivith 

 kinks in the wire. Fortunately, this 

 rarely happened. 



trawl has reached the bottom, but provided that the vessel has maintained 

 a steady speed while it was being lowered, it may be assumed that it 

 reaches the bottom when the wire forms the correct angle after the cal- 

 culated length has been paid out. If the angle is too small the speed of 

 the propellers must be carefully reduced; and if too big, increased. The 

 bottom is checked throughout by means of the echo-sounder, so that 

 trawling can be discontinued should the configuration of the bottom be- 

 come too irregular. It is also valuable to keep account of the tension of 

 the wire, which can be done by means of a simple instrument known as 

 a dynamometer. In certain cases it may be possible to avoid the loss of 

 a trawl if an alarming increase in tension is observed in time and trawling 

 is stopped. But as tension also varies with the direction of the wire it may 

 be difficult to decide wheter increased tension is due to the boards having 

 dug into the bottom or to the trawl being full of clay. Many oceanic 

 research ships ha\e employed an "accumulator" to protect the wire against 



