STEERING GEARSTEERING GEAR(a) Compare difference between four rams type and rotary vane type steering systems.(b) Sketch of above systems.(c) Define hunting arrangement

DIFFERENCE BETWEEN RAM TYPE & ROTARY TYPE

Nature Ram Type Rotary type

Power Electro hydraulic Electro hydraulic

Pump Variable out put delivery pump .

Withstan maximum pressure about 170 bar

Constant output delivery pump

Limited pressure about 90 bar.

Rudder

actuator

Actuated by tiller arm , swivel block , cross

head , ram with cylinder 2 or 4 ram type

Rotary vanes fixed on stator and rotor with

single or double hydraulic chamber.

Control Control by tele-motor system with hunting

gear arrangement

Control by solenoid valve by mechanically or

electrically.

Design , weight

and space

Bulky and rigid design , Heavier weight

Larger space and power require .

Robust than vane type.

Compact design ,lighter in weight with small

space , lower power require for same load.

Not robust than ram type.

Suitability Suitable for all sizes and type of ships.Suitable only for small and medium size of ship.

Because vane tips are not strong enough for

large ship gears.

Wear down Being more rigid design , allow severe

condition and wear down

Wear down cannot be tolerated due to very fine

clearance for tightness

Cost High initial cost Low initial cost

Torque Rudder turning torque is not even depend

on angle. 120 ~ 160 KNm 2 ram

250 ~ 1000 KNm 4 ram

Even at every angle.

Torque capacity attain up to 3000 KnM.

Shock Excessive shock from rudder is transmitted

through ram with cylinder , then to ship

structure

Excessive shock from rudder is transmitted

through vanes to stator , then to actuator

bracket to ship structure.

Cho MyintCho MyintFirst EngineerFirst Engineer

M.F.S.LM.F.S.L

STEERING GEARSTEERING GEAR

Rudder Angle Limited rudder angle 35 ‘ to both sides Wide range of rudder angle.

3 Vane type can give 70 ~ 80 ‘ ( 35 ~ 40 ‘ each )

2 Vane type can give 130 ‘ ( 65 ‘ each )

Time taken Within 30 second from hard to hard turning

from both sides.

Within 25 ~ 28 second for hard to hard turning

from both sides.

Leakage Can utilize with small leakage Leakage or broken vane may cause system

failure

Maintenance Proper tightening of gland packing and

routine maintenance is necessary

Less maintenance compare to ram type.

Hunting gear arrangement

C1 C

B B1

A A1

The linkage of the floating lever from telemotor, pump and rudder stock , form the hunting gear . The telemotor is the receiver of the hydraulic remote control system from the wheel on the bridge. The pump control is moved by the telemotor through a floating lever. The other end of this lever, is connected through a safety spring link to the rudder stock or tiller.

The pump deliver oil , only when the steering wheel is moved. The hunting gear provide the return of pump operating to neutral as soon as the steering wheel stopped by helmsman. So , the rudder is stand still corresponding to the wheel position until another movement of wheel and telemotor.

The sketch shows simply, the operation of the hunting gear. The telemotor moves the end of the floating rod A to A1 and the pump control is moved, therefore from B to B1. Pumping of the hydraulic oil causes movement of the rams and the end of rod C moves to C1 thus causing the pump control to he pulled back to the neutral position B. If the rudder is rotate by the heavy sea through lifting of the shock valves, the hunting gear is moves by the tiller. This put the pump to work and the rudder will be restored to its previous position.

Cho MyintCho MyintFirst EngineerFirst Engineer

M.F.S.LM.F.S.L

Variable

Delivery pump

STEERING GEARSTEERING GEAR

Cho MyintCho MyintFirst EngineerFirst Engineer

M.F.S.LM.F.S.L