TRAWLING FOR FORAGE ORGANISMS IN CENTRAL PACIFIC 



275 



STRfiMtN LINER WSCe 



FiGUBE 5. — Diagram of the 6-foot beam trawl, showing the arrangement of weight and bridle lines. 



metrically with the assumption that the towing 

 wire described a straight line. 



6- FOOT ISAACS-KIDD TRAWL 



A scaled down, 6-foot model of the Isaacs-Kidd 

 trawl was constructed from plans provided by 

 Scripps Institution of Oceanography for 10- and 

 15-foot models. The net is 28 feet in length with 

 the forward section of iy2-inch mesh (stretched 



Table 3. — To%oing tensions obtained with the 1-meter ring 

 trawl, measured with a dynamometer, on Charles H. 

 Gilbert cruise 13 



measure) No. 9 cotton twine; the middle section 

 is of 34-inch mesh and the rear section of lA-inch 

 mesh (fig. 7). The cod end is lined with stramin 

 or with No. 14XXX silk grit gauze. Since the 

 diving vane of the trawl e.xerted a strong depress- 

 ing action, no extra weights were needed. 



This trawl was hauled from the Manning and 

 the Smith at sj^eeds of 4 to 6 knots, on a towline 

 of i/4-inch wire roi>e. At these speeds and with 

 100 to 300 meters of wire out, the towing tension 

 ranged from 600 to 1,200 pounds. 



Devereaux and Winsett (1953) provide data on 

 the shape of the towing wire for the 10- and 15- 

 foot models of the Isaacs-Kidd trawl during tow- 

 ing. Because of the depressing action of the diving 

 vane, the straight-line assumption could not be 

 applied when we calculated hauling depths. Since 

 a suitable depth meter was not available, we esti- 

 mated the curvature of the towing wire and the 

 trawl depth by a method described by Hida and 

 King (1955), which required frequent measure- 

 ment during the haul of wire angle and amount 



