Some very simple devices for various oceanographical uses 1 7 1 



Though insufficiently acquainted with the latest achievements of Dr. J. Scharfe of 

 the Net Research Institute at Hamburg, who has carried out some very interesting 

 investigations of the pelagic trawl with the aid of instruments specially developed for 

 the purpose (Scharfe, 1953), the writer knows of no such determination ever having 

 been made as yet, but there seems no real need for the complexities of a recording 

 instrument which would travel all the way along the warps to effect it. It seems amply 

 good enough to measure the slope of a warp at a lot of discrete points where slope 

 alone is the matter of interest, and to measure slope and direction at many points 

 along the two warps where both slope and separation (roughly telling net gape) are 

 wanted. 



It could well be that, after learning the average slope of the whole warp lengths for 

 different speeds of tow and various lengths of warp veered (which average slope would 

 reveal fishing depth), it might be found possible to apply " corrections " to the readings 

 of the deck inclinometer used to measure the entry angle of the warps. It is worth 

 hoping that such " corrections " could become known for all lengths of warp out and 

 all towing speeds so that the easily observed entry angles could be converted into 

 approximate mean slope values and a table of implied net depths consulted with 

 confidence. 



WARP SLOPE 



Where only one cable towed astern is being investigated, the rectangular instrument 

 pictured (Fig. 2a and 2b) is a suitable and convenient one to use. It is a slender box 

 of about cigar-box size and shape with front and back of clear perspex and is filled 

 with gelatine solution only. Inside is a pendulum which can move freely so long as the 

 gelatine solution remains liquid after prior immersion of the instrument in a bath of 

 hot water. It is intentionally not fitted to the warp or towing rope by clamps, but 

 through the medium of the bracket shown, which is secured on the warp, thin wire, or 

 rope, by winding round it and the warp a strong stretched rubber thong, just as a 

 runner bean in the garden winds itself on to and up its supporting stick. 



Using such a cheap and easy method of attachment, one can affix all manner of 

 instruments to all sizes of wire, cable, or rope and secure a firm non-slip grip without 



trouble. 



The rather heavy inclinometer is pictured fastened securely on to a very smooth 

 brass wire no thicker than ordinary water-bottle wire. To facilitate attachment by 

 one person working alone, the side of the bracket which is bound on to the warp 

 has since been fitted with prongs after the manner of the wooden rods fixed across 

 the tops of some of the bottles pictured. This makes it very easy to effect attachment 

 by winding a lot of stretched office rubber bands round and round bracket-rod and 

 warp in an obvious manner. 



It does not matter if the warp twists at all because the rectangular inclinometer as 

 pictured can swing all round it and still maintain parallelism— just as the passenger 

 cages of the " Big Wheel " at a fair move round its axle. 



There is a fiUing point (unscrew the domed knob) and also an air vent controlled 

 by a removable grub screw. Inwards thumb and finger pressure exerted on the two 

 small spring-loaded levers either side of the filler knob releases the rectangular box 

 from its bracket. 



