THE TECHNiqUE OF TRAWLING 



113 



The heart of the expedition, 

 the large trawling winch. 



resistance is almost perpendicular to the cylinder axis, as shown in the 

 drawing at the foot of the page. 



If a wire of uniform thickness is dragged through the water unweighted 

 and without touching the bottom it will form a straight line, the direction 

 being determined by the resultant of the transversal resistance and the 

 weight of the wire, the longitudinal resistance drag being without influ- 

 ence on the position of the wire. The greater the speed, the more the 

 wire will approach the horizontal position; and the heavier the wire, 

 the more it will approach the vertical. True, the resistance will increase 

 with the diameter, but the weight will increase still faster. The resistance 

 has a sustaining effect on the wire which partly offsets the effects of weight, 

 with the result that the tension diminishes in ratio with increasing speed, 

 at any rate in the speeds met with in practice. 



If a wire is pulling a trawl, it can be assumed that just in front of the 

 trawl it drags the bottom, and so is horizontal at its lower end. A mathe- 

 matical calculation, which I cannot go into here, shows that in this case 

 the wire on its way up to the vessel strives for the same position as it 

 would have occupied if unloaded and not touching the bottom. This 

 occurs the more speedly the less the tension produced by the trawl. 

 The drawing on page 1 1 4 shows the positions in deep-sea trawling of 

 three wires of various thicknesses. It will be seen that the wires form a 

 virtually straight line even quite near the bottom, and that the direction 

 when close to the ship differs but slightly from the direction of the unload- 

 ed wire. The calculation gives the length of wire as a function of the 



