of the, Fishery Board for Scotland. 121 



II. Depths 5} to ^ fathoms. Length of warp, 2-10 feet. 



(1) Speed at 71 revolutions. 



a Apparent dist;ince between boards, calculated from divergence of warjis, 



36 feet 6 inches. 

 I) Distance between bladders, 41 feet. 

 c String between boards, 34 feet 6 inches, broken. 



,, ,, ,, 36 feet, unbroken. 



(2) Speed at 109 revolutions. 



a Apparent distance between boards, calculated from divergence of warps, 



3.5-1 feet.. 

 b Distance between bladders, 37 feet 2 inches. 



III. fj?, to 9|^ fathoms. One hour's ordinary drag. 



" h Distance between bladders, (1) 26 feet 8 inches. 



(2) 28 „ 9 „ 



(3) 35 „ 10 „ 

 c Strings between boards. 



(1) 35 feet long, came up unbroken. 



(2) 38 feet long, reduced by a running hitch to 31 feet 6 inches, 



came up with hitch partly run, and measured 33 feet 2 inches. 



In order to test the value of the data obtained a beam trawl with 

 25 feet beam Ava.s also nsed. The bladders were tied to the ends of the 

 beam and three measurements were taken of their distance apart on 

 the surface during the drag ; they were as follows — 22 feet 6 inches, 23 

 feet 11^ inches, 23 feet 3| inches, the mean being 23 feet 3 inches. 

 This experiment showed that the bladders slightly converged. The 

 trawl was towed at ordinaiy speed, and two warps were used, one at 

 either end, as with the otter-trawl, in order to test the data obtained 

 from measuring the angle between the warps. At ordinary speed this 

 indicated 18-3 feet, or 67 feet less than it really was ; at full speed 

 the indicated distance apart at the beam was 19'1 feet, or 5*9 feet less 

 than the real distance. 



The data obtained by the above experiments in regard to the spread 

 of the otter-trawl vary to some extent, but they show, I think, that 

 the distance between the boards when the net is fishing on the bottom 

 is less than is usually supposed. According to the calculation assumed 

 by the net-makers (i.e., the deduction of one-third of the length of the 

 headline), the spread in the above experiments ought to have been about 

 42-7 feet. The check experiment with the beam-trawl proves, as one 

 might expect, that the distance as calculated from the angle between 

 the warps is unreliable, and that the distance is usually greater than 

 this method indicates, and anomalies occur. The bladder tests gave 

 better results, and if we add to the measurements the amount which 

 the beam-trawl experiment showed was lost by convergence, viz., one 

 foot 9 inches, the mean distance indicated would be at ordinary speeds 

 33 feet 4 inches, and at full speed 34 feet 3 inches. But in some 

 cases the bladders diverged, e.g., the experiments in which the 

 distance between them was 41 feet, while a string between the boards, 

 36 feet long, remained unbroken. The most reliable results are, I 

 think, obtained by the string tests. The string used was the ordinary 

 hemp twine of which the trawl-nets are made, and while it is strong 

 enough to resist rupture from pressure by the water, it is, of course, 

 much too slender to bear a strain from the boards. Cases in which 

 it is broken are not alone convincing, since its rupture may happen 

 accidentally, but Avhen it comes up intact it proves that the boards 

 have not been further apart than its length. In the experiments 

 above described it remained unbroken when 45, 40, 36, and 35 feet 

 long ; it was broken when 34 feet 6 inches long, and in the experiment 

 with a hitch on it it measured 33 feet 2 inches. 



It may be fairly concluded that in these experiments the width of 

 the mouth of the net when fishing was, as a rule, between 33 and 35 

 feet, although the headline was 64 feet. This would indicate the 



