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Rudder carrier bearing & Steering gear arrangement for cargo ship

The rudder carrier bearing (Figure below) takes the weight of the rudder on a grease lubricated thrust face. The rudder stock is located by the journal beneath, also grease lubricated.

Support for the bearing is provided by framing beneath the steering gear deck. There is thicker deck plating in the area beneath the carrier bearing and the latter may be supported on steel chocks. The base of the carrier bearing is located by side chocks welded to the deck. The carrier may be of meehanite with a gunmetal thrust ring and bush. Carrier bearing components are split as necessary for removal or replacement. Screw down (hand) lubricators may be fitted but automatic lubricators are common. The grease used for lubrication is of a water resistant type (calcium soap base with graphite).

The tiller (Figure 9.1) is keyed to the rudder stock and is of forged or cast steel with one (or two for a four ram gear) arms, machined smooth to slide in a swivel block arrangement designed to convert linear movement of the rams to the rotary movement of the tiller arms and rudder stock. This particular device, known as a Rapson slide, is used for many, but not all, ram type gears. The rams are one-piece steel forgings, with the working surface ground to a high finish. Each pair of Rapson slide rams, is bolted together, the joined ends being bored vertically and bushed to form top and bottom bearings for the projecting spigots on the swivel block. Crosshead slippers, bolted to the face of the central section of the rams, slide on the machined surfaces of the guide beam. Guide beams also serve to brace each pair of cylinders against the tendency for them to be pushed apart by the hydraulic pressure. The cylinders have substantial feet bolted to the stools on which the gear is mounted.

Rudder carrier bearing
Figure : Rudder carrier bearing

Carrier with conical seat
Figure : Carrier with conical seat

Weardown of the carrier bearing is monitored by periodically measuring the clearance marked. The original clearance is usually about 20mm. An alternative type of carrier bearing with a conical seat (Figure 9.2) has the advantage that the seat and side wall will locate the rudder stock. The angle of the conical seat is shallow to prevent binding.

Bearing weardown occurs over a period of time, and allowance is made in the construction of the steering gear (see Figure 9.1) for a small vertical drop of the rudder stock. This weardown allowance is checked periodically and restored as necessary. Lifting of the rudder and stock by heavy weather can be limited by jumping stops between the upper surface of the rudder and the stern frame.

The usual limit for movement of the rudder, is 35 each way from the mid position and this is controlled by the telemotor. External rudder stops if fitted, would limit movement to, say, 39 from the mid position. The steering gear itself will also impose a limit on rudder movement but with hydraulic oil loss and the ship stopped in heavy weather, there may be severe damage to the gear. The telemotor control imposes the usual 35 limit.



Summarized below various ship steering gears general guideline:
  1. Ship Steering gear failures and safeguards

  2. The hydraulic circuit incorporates an arrangement of stop and bypass valves in the chest VC, which enable the gear to be operated on all four or on any two adjacent cylinders but not with two diagonally disposed cylinders. ......

  3. Four-ram electro-hydraulic steering gear mechanism

  4. The hydraulic circuit incorporates an arrangement of stop and bypass valves in the chest VC, which enable the gear to be operated on all four or on any two adjacent cylinders but not with two diagonally disposed cylinders. ......

  5. Enclosed hunting gear

  6. The light construction of the combined control and hunting gears is possible because the forces concerned are moderate. The self-contained unit is self-lubricating, and contained in an oil-tight case. ......

  7. Ship steering control mechanism- use of Hydraulic telemotor

  8. The telemotor has become, on many vessels, the stand-by steering control mechanism, used only when the electric or automatic steering fails. It comprises a transmitter on the bridge and a receiver connected to the steering gear variable delivery pump, through the hunting gear. ......

  9. Two-ram electro-hydraulic steering gear with variable delivery pumps

  10. An arrangement of a two-ram steering gear with variable delivery pumps may have a torque capacity of 120-650 kNm. The cylinders for this gear are of cast steel but the rarns comprise a one-piece steel forging with integral pins to transmit the movement through cod pieces which slide in the jaws of a forked tiller end. ......

  11. Rudder carrier bearing & Steering gear

  12. The rudder carrier bearing takes the weight of the rudder on a grease lubricated thrust face. The rudder stock is located by the journal beneath, also grease lubricated ......

  13. Small hand and power gears - Ship steering systems

  14. A simpler variant of the electro-hydraulic gear, for small ships requiring rudder torques below say, 150 kNm ......

  15. Four ram gear with servo-controlled axial cylinder pumps

  16. Variants of the servo-controlled swash plate axial cylinder pump are capable of working at 210 bar. Each pump is complete with its own torque motor, servo-valve, cut-off mechanism, shut-off valve and oil cooler. ......

  17. Vane type gear - provides security of four ram steering gear

  18. These may be regarded as equivalent to a two-ram gear, with torque capacities depending on size. An assembly of two rotary vane gears, one above the other, provides the security of a four ram gear. ......

  19. Details of two ram hydraulic steering gear arrangement

  20. When the main pumps are at no-stroke, the auxiliary pumps dischar. to the reservoir via a pressure-limiting valve PC20, set at 20 bar, and to t pump casings. When the main pumps are on-stroke, the auxiliary pump discharge to the main pump suction. ......




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