Patent GB-369588-A (GB)
Title: An improved ship's log
IPC: G01P5/02
Filed: 1930-11-20
Abstract: 369,588. Ships' logs. BREWERTON, A. E., 39, Higher Drive, Purley, Surrey. Nov. 20, 1930, No. 34938. [Class 69 (i).] In a ship's log, a displaceable member is immersed in the sea so as to be subject to the dynamic pressure of the water and a second force is applied to the said member to counterbalance the dynamic pressure, the said force being measured to provide an indication of the speed of the ship. A simple form of integrating mechanism may be provided if it is desired to obtain an indication or record of the total distance travelled by the ship. In one form, shown in the Figure, a disc 1 is fixed to the lower end of a rod 2 which projects through the hull of the ship. The rod 2 is carried by a diaphragm 3 which forms a watertight joint and acts as a fulcrum and is supported in a casing 4 attached to the hull of the ship. The upper end of the rod 2 is formed as a contact 6 which co-operates with fixed contacts 7, 8 connected to electromagnets 9, 10, the latter being connected to the same source of supply as the contact 6. The outer end of a pivoted lever 18 projects between the electromagnets 9, 10, the other end of the lever 18 being provided with rollers 19 which on movement of the lever 18 operate a reversing clutch 14 .. 17, the member 16 being keyed to the shaft 20, driven by gearing 12, 13 from a continuously rotating motor 11. The rotation of the wheel 17 turns a shaft 21 which drives through gearing 22 .. 25 a shaft 26 carrying a cam 27 to which is attached one end of a spring 5 the other end being attached to the rod 2. The shape of the cam 27 is so designed that the tension in the spring 5 increases proportionately to the square of the angular movement of the shaft 26 so that although the pressure on the disc 1 varies as the square of the velocity of the ship, the angular movement of a pointer 28 fixed to the shaft 26 over a fixed dial 31 is directly proportional to the velocity of the ship. The effective shape of the cam 27 may be varied by a pivotally mounted part 29 which is adjusted by a screw 30. A step-by-step transmitter 32 is mounted on the shaft 21 so as to transmit the indications of speed to distant repeater instruments. When the ship is in motion, the deflection of the disc 1 causes rods 2 to close the contacts 6, 7. The magnet 9 is energized and the clutch 16 engages the wheel 14 to drive the shafts 21, 26 and apply tension to the spring 5. The latter is wound up until its tension overbalances the pressure on the disc 1 whereupon contact 6 separates from the contact 7. The clutch 16 is then disengaged and as long as the speed is steady the pointer 28 remains steady indicating on the dial 31 the true speed. If the speed is reduced, the spring 5 draws the contact 6 into engagement with the contact 8, thus energizing the magnet 10 and reversing the wheel 17 and thus the shaft 26. The tension of the spring 5 is thus released until the reduced pressure on the disc 1 separates the contacts 6, 8. The pointer 28 will then indicate the reduced speed. To indicate the total distance travelled, the motor 11 is connected by gearing 33, 34 to a shaft 35 driven at a constant speed and on which a sleeve 36 can move up and down being prevented from rotation by a fixed pin 38 engaging a slot 37 therein. A member 39 with a worm 39a thereon is screwed on to the sleeve 36, the worm 39a engaging a worm 40 on the shaft 21 but as the member 39 cannot move axially it causes the sleeve 36 to move along the shaft 35 an amount corresponding to the speed. On the lower part of the shaft 35 is a spring-controlled clutch member 41 having an inclined surface which is met once in each revolution by a roller 44 attached to the sleeve 36 and thus brings the member 41 into gear with a spring-controlled member 45. A pair of contacts 48 complete a circuit once in each revolution of the member 45 said circuit operating a suitable ratchet motor for indicating in a repeat instrument, the distance run. Instead of the diaphragm 3, the rod 2 may be provided with. a spherical projection which is forced on to an annular seating in the part 4 by a spring. In a modification, the displaceable member consists of a slidably mounted vane and the pressure counterbalancing the pressure on the vane is applied to a slide valve or piston enclosed in a chamber, the pressure of air behind the piston being indicated on a gauge in terms of the speed. In a further modification, an impeller is moved through a limited angle by the dynamic pressure and the counterbalancing force is measured electrically in terms of the speed.