468 DISCOVERY REPORTS 



high, 8| in. wide and 14I in. long; this contained the internal mechanism which could 

 be slid out for adjustment and loading through doors opening on the left-hand side 

 of the body. In front of this box section the body tapers to the opening of the water 

 tunnel and behind it tapers to a point, the water exit being on the underside of this tail 

 section. The total length is 3 ft. 4 in. The dimensions of the various parts may be read 

 off from the scale drawings in the figures. By stout brackets, the diving plane is fixed 

 below the body so that the leading edge is directly below the front end of the box 

 section. Above is fixed a towing eye to which is attached a cylindrical shock absorber 

 designed to reduce the vibrational fatigue on the towing cable (see p. 489). To the 

 tapering tail section are fixed horizontal fins at the sides (continuous behind) and a 

 large vertical fin above; in this vertical fin is inset a rudder which may be set to 

 counteract any tendency to go to starboard due to the rotation of the propeller. 



The propeller, with adjustable blades, is situated aft and is protected by a ring 

 outside, a bar behind combined with a lifting handle, and by a pair of rods on each side 

 connecting the ring to the front of the vertical fin. These guard rods were later additions 

 found necessary to prevent fish, seaweed, etc., being caught in the propeller blades. On 

 one occasion a dogfish was found decapitated and jammed in the propeller ring. The 

 propeller shaft passes forward through a bearing, divides the vertical fin into two parts, 

 and connects by a flexible joint with a drive shaft entering the gear box. The gear box, 

 which is kept filled with oil, is situated in the top of the box body ; in the illustrations its 

 top will be seen projecting upwards as a dome furnished with a cap for replenishing 

 the oil supply. 



The opening to the water tunnel in front is i\ in. square, but may be reduced to 

 1 or I in. square (or less) by fitting in small nose pieces. The tunnel widens out to 

 a rectangular cross-section 4 by i| in., where it joins the tunnel passing into the internal 

 mechanism frame which can be slid out for loading. The movable section of the tunnel 

 (i.e. in the mechanism frame) slides into grooves in the fixed part of the tunnel in front 

 and behind and when closed makes a tight joint. The tunnel continues behind the 

 movable frame to open beneath the tail section. All the space between the water tunnel 

 and the tapering body wall of the front section is filled with lead to bring the centre of 

 gravity of the machine as far forward as possible. The machine weighs 156 lb. (in- 

 cluding the shock absorber), and the centre of balance (with the shock absorber re- 

 moved) is 12^ in. behind the front of the machine (without nose cap). When first made 

 the machine was fitted with a buoyancy tank in the tail section above the exit to the 

 water tunnel, but this was found to be unnecessary. 



Through the internal mechanism frame the water tunnel takes a slightly sigmoid 

 path in the vertical plane in order that the minimum of space should be wasted in 

 arranging the system of spools and storage tank. As it passes backwards the tunnel 

 gradually widens to a cross-section 4 in. wide and 2 in. deep at the point where it is 

 traversed by the gauze banding (see Fig. 10). In plan the tunnel is slightly asymmetrical 

 on account of the mechanism frame having to be displaced to the left to allow space on 

 the right for the worm drive from the gear box above (see Fig. 4) and the train of gear 



