Question

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 reasons the best angular position to lock the steering gear (4)

(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. (6)

(c) State the consequences of the wear down clearances being reduced to less than zero. (6)

Answer 1

Part (a)

Emergency Locking Device:

In the case of a hydraulic ram-type steering gear, the gear can be brought to a halt in an emergency situation by employing hydraulic locking. This is achieved by closing the manual isolation valves (A, B, C, and D) on the individual hydraulic cylinders. By isolating the cylinders, the movement of the rams is stopped, effectively locking the steering gear.

Mechanical Locking: Three methods are available:

A spanner is fitted to the rudder stock head nut and secured to the ship's structure, directly preventing rudder movement.
If provided, tow gigs are fitted between the crosshead and cylinder base, mechanically locking the steering mechanism.
(Assuming a braking system is integrated into the design) Engaging the brake will prevent any movement of the rudder.

The midship position is the optimal angle for locking the steering gear when the ship is under tow or in need of emergency locking. At this position, the ship will follow the wake of the towing vessel without generating unwanted lateral forces. If the rudder were locked at any angle other than midship, it would cause the ship to turn or resist movement, potentially causing instability or drift.

Part (b)

Steering gear cross-head top clearance must be substantially greater than jumping clearance so as to avoid any damage to the steering gear in the event of grounding

Jumping clearance is provided to prevent the damage of steering gear due to the jumping of the rudder in heavy seas.

Steering gear crosshead bottom clearance should be sufficient to accommodate for the wear of the rudder carrier bearing. This should be greater than the riding washer clearance.

Clearance expected with new steering gear:

Jumping (top) clearance: 3-6mm, depending on the diameter of the rudder stock
Wear down (bottom) clearance: 20-25mm

Part (c)

If the wear-down clearance is reduced to less than zero, the rudder carrier ring will be in contact with the riding washer. This will result in the rams carrying the full load of the rudder, leading to excessive torque. This could cause bending or, in extreme cases, breakage of the rams.

✓ Verified Model Answer (Text Solution)

Emergency Locking Device:

Steering gear cross-head top clearance must be substantially greater than jumping clearance so as to avoid any damage to the steering gear in the event of grounding

Clearance expected with new steering gear:

If the wear-down clearance is reduced to less than zero, the rudder carrier ring will be in contact with the riding washer. This will result in the rams carrying the full load of the rudder, leading to excessive torque. This could cause bending or, in extreme cases, breakage of the rams.