T.S. Patriot State Engineering Manual

Patriot State was the training ship of the Massachusetts Maritime Academy from 1986 to 1998.

Steering Gear Operation

In normal operation, the control of the steering gear is accomplished by the dual control gyro pilot steering system and the linear hydraulic power unit. If either of these two systems fail, the steering gear may be controlled by the trick wheel located in the steering engine room or in the event that we have failure of the other systems, the steering gear can be actuated by use of the hand operated gerotor hydraulic pump.

Selection of either Hele Shaw pump or transfer of operation from one pump to the other is accomplished by putting the desired push-button in the pilot house. An electric brake is provided on the back end of the motor driving each Hele Shaw pump to prevent reversed motion of the idle pump when changing from one unit to another or in the event of a power failure with the pumps on stroke.

When the steering wheel on the gyro pilot steering stand is turned, either in the automatic (gyro-compass controlled) or hand electric mode, the control potentiometer sends an electric signal which energizes one of the solenoids of the direction a valve attached to the linear hydraulic power unit. The solenoid pushes the pilot spool of the directional valve off center allowing hydraulic fluid pumped from the compensated hydraulic fluid pumped from the compensated hydraulic pump unit to apply pressure to one end of the power unit cylinder and connects the opposite end of the cylinder to the return line. The direction of hydraulic fluid flow, and thus the direction of the power unit piston rod movement, will depend upon which solenoid is energized.

Movement of the power unit piston rod places one, or both, of the Hele Shaw pumps on stroke via the differential gear train.

The linear hydraulic power unit piston rod keeps moving until the repeat back potentiometer actuated by a parallel rack which moves with the piston rod, generates a follow-up signal which de-energizes the solenoid and stops movement of the piston rod.

The Hele Shaw pump being placed on stroke pumps hydraulic fluid to the hydraulic rams which cause the rudder stock, and thus the rudder stock causing the follow-up shaft to rotate. This rotation of the follow-up shaft via the differential gear train moves the floating ring of the Hele Shaw pump taking off stroke and locking the rudder in the position selected by the helm.

The linear hydraulic power unit and thus the rudder remains stationary until a new movement of the steering wheel is made.

Steering With Trick Wheel

The steering gear can be controlled by a horizontal trick wheel located immediately above the differential gear train assembly (see figure on page 8-15). The trick wheel is utilized to control the movement, and thus the stroke, of the Hele Shaw pump in the event of failure of the gyro pilot steering control. To utilize the trick wheel, the pin connecting the linear hydraulic power units to the differential gear train must be disconnected and the pin connecting the trick wheel to the differential gear train inserted. A mechanical rudder angle indicator and gyro repeating compass is located in close proximity to the trick wheel to assist in the steering.

The number of turns of the trick wheel to move the rudder from one hardover position to the other hardover position is 9.1 turns.

Obviously, in order to use the trick wheel, the Hele Shaw pumps must be operable.

Steering With Two Cylinders

Provisions are made for steering by power or hand with two cylinders only as follows:

1. By after cylinders with forward cylinders by-passed.
2. By port cylinders with starboard cylinders by-passed.
3. By forward cylinders with after cylinders by-passed.
4. By starboard cylinders with port cylinders by-passed.

In the case of failure of a cylinder, when steering, the defective pair may be by-passed through the low pressure piping system, and gradually drained to the tanks without shutting down.

Some failures of the high pressure system or cylinders may make the necessary to drain the defective cylinders before hand steering. The hydraulic oil may be allowed to escape from the defective cylinders through the air vents or from disconnected piping.

Maintenance

The emergency hydraulic system should be checked periodically and it is well to make sure that this, as well as the pump is in good operating condition. The following points should be checked:

1. Make sure that system is full of oil.
2. Be sure system is free of air.
3. Check setting of relief valves. The relief valve setting should be between 600 and 650 psi. A leaking or improperly adjusted relief valve may prevent sufficient build-up of pressure. The relief valve should not be set for more than 650 psi. maximum.
4. Should the pump fail to turn over when force is applied to the cranks, the pump should be taken apart and all parts examined carefully. You may find:
   1. Gum in oil may have caused the parts to stick to each other.
   2. Foreign matter in the oil may be causing a wedging action between the teeth of the Gerotors.
   3. The locking spring may be binding in its sleeve. If examination of the rocking spring indicates that it cannot be repaired, it may be left out of the pump. When the pump is operated without the locking spring, provisions should be made for holding the crank in position to prevent kick-back which the spring had automatically taken care of prior to its removal.

Direct comments to William Haynes whaynes@maritime.edu
Mon, Jul 1, 1996
TSPS Engineering Manual ©1995 Massachusetts Maritime Academy