Question

(a) Describe with the aid of sketches where necessary a vane type steering gear showing how to weight of the rudder and stock are carried and the arrangement that allow for wear down (6)

(b) State how the vanes described in (a) are secured and the method of sealing the edges. (5)

(c) State how, if necessary, the steering gear is locked for rudder maintenance. (5)

Answer 1

Part (a)

A vane-type steering gear uses a rotor and stator mechanism where the vanes create hydraulic chambers to control the movement of the rudder.

The rotor is fitted to the tapered rudder stock. The rudder stock carries the weight of the rudder, supported by a rudder carrier bearing.
The stator is fixed to the ship’s structure, forming a rigid support.
The fixed vanes are evenly spaced inside the stator bore, while the rotating vanes are equally spaced on the rotor.
These vanes form two sets of pressure chambers in the annular space between the rotor and stator. Hydraulic fluid is supplied at pressure to one set of chambers, causing the rotor and rudder to rotate in the required direction based on the steering order from the wheelhouse.
The weight of the rudder and rudder stock is carried by the rudder carrier bearing, which is mounted on steel chocks supported by thicker deck plating to ensure stability and handle the load.
There is a vertical clearance between the stator flange and the anchor bracket to allow for rudder "jump" (vertical movement).
Another clearance exists between the top of the anchor bracket and the stator flange to accommodate for rudder wear down or rudder drop over time. The total clearance provided is around 38 mm, allowing the system to absorb wear and vertical movement without affecting performance.

Part (b)

Vanes Securing and Sealing:

The fixed and rotary vanes are made from modular cast iron and are secured to the rotor and stator using high-tensile steel dowel pins and cap screws to maintain strength and prevent detachment under stress. A key is fitted along the length of the rotary vanes to provide additional reinforcement and ensure the strength of the rotor.
The sealing of the vanes is achieved using sealing strips made of cast iron. These strips are fitted into grooves along the edges of the vanes. The sealing strips are backed by elastically loaded synthetic rubber, which provides a tight seal by pressing against the faces of both the fixed and rotating vanes. This arrangement prevents hydraulic fluid leakage.

Part (c)

The steering gear can be locked for maintenance using either hydraulic or mechanical methods:

Hydraulic Locking: This involves closing the manual isolating valves provided for each cylinder (in ram-type systems) or each vane chamber (in vane-type systems). This prevents hydraulic fluid flow, thus immobilizing the rudder.
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.

✓ Verified Model Answer (Text Solution)

A vane-type steering gear uses a rotor and stator mechanism where the vanes create hydraulic chambers to control the movement of the rudder.

Vanes Securing and Sealing:

The steering gear can be locked for maintenance using either hydraulic or mechanical methods: