meters have "automatic" blocks that release 

 the impeller blades when water flows 

 through them.) 



The stop watch is started when the flow- 

 meter (s) is seen to sink below the surf- 

 ace of the water. 



30 70 30 AO 50 60 70 80 90 

 STATION DEPm IN FAmOMS 



100 110 120 130 



Figure 11. — Depth-of-tow graph. — To be used if station depth is 130 fathoms or 

 less when standard tow is 300 m wire out. If standard tow is less than 300 m wire 

 out, e.g., 100 m or 200 m, the graph is still applicable. For 100-m standard tow, 

 use graph when station depth is 45 fathoms (82 m) or less. For 200-m standard 

 tow, use graph when station depth is 165 fathoms or less. Except for the very 

 shallow depths, 20 fathoms or less, where a tow is practically all at the surface, 

 the points on the diagonal line indicating the amounts of wire to be paid out are 

 calculated to keep the net approximately 10 to 18 m off the bottom. This is con- 

 sidered a safe margin, and it is recommended that no changes be made when one 

 considers that only the rocking of a ship in heavy seas can reduce an 8-m safety 

 margin to 5 or 3 m. 



13 



