CHAP. XX.] 



SWEEPING BY BOATS 



447 



sextant angle between them, and app]3nng angle (see Fig. 104), 

 the head wires of otters should be slightly shortened, or, if 

 preferred, the speed of boat sUghtly reduced, which will have 

 the effect of making them close, though reduction of speed will 

 also cause sweep to be slightly deeper owing to otters then being 

 towed shghtly below surface. 



A man is stationed at each machine watching otters, with one 

 hand on wire abaft machine and the other on thumb -screw 

 of band brake. Immediately sweep fouls a rock the otters 

 converge and dive; the machine man eases brake and lets out 



Plan of Otter Board 



Length 35! 2 inches 

 Depth 18 inches 

 Made of ll's Kauri Pine 

 Total weight 46 lbs. 

 Screw Eije-boHs 2in. fronr ends 



,, ,, „ 7 in. from Top and bottom 



Fig. 105. 



wire to ease strain till boat has gathered sternway; the kite 

 wires are then hove in, otter boards taken off, and sweep 

 cleared. 



If sweep is badly foul of a rock, as is likely to occur with coral, 

 by heaving in kite wires, which have over three times breaking 

 strain of sweep wire, sweep wire can be parted, kites hauled 

 in, and new sweep wire fitted very quickly. 



Otter boards may be secured to kite wires either by stoppers 

 similar to but stronger than those supplied for sounding wire, 

 or by a wire seizing through otter's thimble, round kite wire, 



