Answer MEP Question 49

Q. With respect to hydraulic Ram steering gears; 

A. What emergency locking device can be used in order to speedily bring the steering gear to rest? State one reason the best angular position to lock the steering gear. 

B. Use a simple sketch to show where the Jumping (top) and wear down (bottom) rudder carrier ring clearances can be measured. Indicate what clearances you would expect with a new steering gear; 

C. State the consequences of the wear down clearances being reduced to less than zero. 

A. What emergency locking device can be used in order to speedily bring the steering gear to rest? State one reason the best angular position to lock the steering gear. 

To speedily bring the steering gear to rest there is a bypass valve in the line connecting the cylinders in operation at a time. This valve is normally closed. Opening the bypass valve will cause a flow of oil to pressure balance in both the opposite cylinders. This will render the rudder free of control from the steering system and due to the water flow from the propeller to the rudder, the rudder will return to the midship position. At this point, isolation valves of the respective cylinders are simultaneously closed and thus the rudder will be hydraulically locked in this position.

The midship position is best for locking the rudder because at this position the rudder will not experience any force from water flow and thus will not cause any tuning moment on the ship.

B. Use a simple sketch to show where the jumping (top) and wear down (bottom) rudder carrier ring 

- The Steering Gear Cross-head top clearance must be substantially greater than the 'Jumping' clearance, so as to prevent any bending moment from damaging the steering gear, in the event of running aground. - The Steering Gear Cross-head bottom clearance should be sufficient to cater for wear in the Rudder Carrier bearing, which could otherwise affect the movement of the rams. - This bottom clearance should be substantially greater than the Riding washer clearance. 

Clearances can be measured. Indicate what clearances you would expect with a new steering gear
1. Rudder drop allowance = 10-15mm
2. Jumping Clearance = 3 mm
The Steering Gear Cross-head top and bottom clearances are of the order of 20 - 25 mm for small to medium-size vessels. Insufficient Riding washer clearance would lead to wear of the carrier bearing. There should be no keel blocks in way of the Skew. 

C. State the consequences of the wear down clearances being reduced to less than zero. Allowable rudder drop should be less than wear down clearance (rudder drop) and it should not be 'zero', if it happens complete load will come on RAMs due to which there will be excessive torque which will cause the RAM to bend or in extreme cases breakage of RAM will occur.


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