steering 01

8/3/2019 Steering 01

http://slidepdf.com/reader/full/steering-01 1/33

Explain theFundamentals of Steering

Theory



CONSIDERATIONS OF SHIP

MANOEUVRABILITY

Maintaining a given course - directional &

dynamic stability Ship response to movement of the control

surfaces

Ability to turn completely within a specifieddistance



Functions and Requirements

of Steering Gear Systems

Directional Control Maneuverability



Manoeuvrability



Manoeuvrability

a. Ease of maintaining course (steering).Directional and dynamic stability.

b. The response to movements of the

rudders, either in initiating or terminating a

rate of change of heading.

c. Turn completely round within a givenspace.



Directional Control

Directional Control can be

achieved by:

• Rudders.

• Rudders and Bow Thrusters

• Vertical Axis Propellers.

(eg Voith-Schneider propeller).



Rudders• Rudder is a servo system

• Hydrodynamic forces and moments on the hull

cause the ship to turn.

•

Fitted aft to benefit from the increased watervelocity induced by the propellers.

• Streamlined form produces:

• Large lift force and minimum drag

• Leading edge sections are designed to reduce

the variation of lift force with the angle of attack.



Steering Limitations

• Typically stalling will occur at an angle

between 35O - 45O.

• Hence the limitations on the max turningangle (helm) of the rudder in most ships is

limited to 35O.

• This avoids stall, loss of speed and large

heel on turning.



HYDRODYNAMIC EFFECT

• STABILISING OR DESTABILISING DESIGNS

•

STABILISING – TENDS TO STEADY UP ON A NEW COURSE

WHEN EXTERNAL FORCES ACT UPON THE

HULL

•

DESTABILISING – WILL NOT STEADY UP ON NEW COURSE

• BILGE KEEL & SHAPE OF HULL



Directional StabilityWhen under way,

• Hydrodynamic forces - stabilizing or

destabilizing effect.

•

A hull will not return to its initial coursewithout an external corrective force.

Directionally stable is when,

• Having suffered a disturbance from a straightpath it tends to take up a new straight line path.

• This moment acts around the point called the

centre of lateral resistance.



Action of Rudder in Turning a Ship

Ships

Head

G

T

J

FR

FH

XCentre of Turning Circle

B

y

V

E a



Action of Rudder in Turning a Ship

Ships

Head

G

T

J

FR

FH


B

y

V

E a



Ships

Head

G

T

J

FR

FH


B

y

V

E a

Radial Force = (D V2 /R )



Linear Theory of Motion



Measurement of

Manoeuvrability

-Dimensional Parameters

-Performance factors



Dimensional

Parameters



The Turning CircleApproach Course

Rudder Execute



Drift AngleApproach Course

Rudder Execute

DriftAngle



AdvanceApproach

Course

Rudder Execute

DriftAngle

Advance at 90o change of heading



TransferApproach

Course

Rudder Execute

DriftAngle


Transfer

at 90o

change

of

heading



Tactical DiameterApproach

Course

Rudder Execute

DriftAngle


Transf er

Tactical

Diameter

at 180o

change of

heading



Diameter of Steady Turning CircleApproach

Course

Rudder Execute

DriftAngle


Transfer

Tactical

DiameterSteady

Turning

Radius



Performance Factors



Loss of speed - caused by increased drag,

normally at 90 O into the turn and be 40%

below the approach speed.

Angle of heel

Turning rate - rate of turn of ships head off

the approach course. For Naval vessels thiscan be as much as 3 degrees/sec.

Performance Factors



Rudder Torque

T a A CP V2 sinq

Where:

A = Rudder Area

CP = Centre of Pressure distance from rudderstock centre line. V2 = Velocity of Ship

q = Rudder angle measured from midships.



Horsepower (max) a T x S

Where:

T = max torque

S = max speed

Rudder Horsepower



Factors affecting Ships

Response to Steering1. Shape of hull form.

2. Speed.

3. Direction of movement.

4. Number of rudders.

5. Rudder shape.

6. Position of rudder.

7. Rate of rudder movement.



STEERING SYSTEM

PERFORMANCE SPECIFICATIONS• Accuracy of control (max misallignment) +-

1%

• 35 deg port to 35 stbd in less than 30 sec

• Must not move max 3 deg beyond max

angle of helm : 38 deg for max helm order

of 35 deg



STEERING

INSTALLATIONS

• Consists of

– Steering gear

• Mechanism to move the rudders to desired position

• Hydraulic actuators

– Steering control system

• Mechanical

• Electrical

• Hydraulic

• Combination of these



STEERING

INSTALLATIONS

• Is to be capable of moving, stopping and

holding the rudders at any angle within the

limits of operation



SYSTEM COMPONENTSRef Chapt 1.29

RUDDER SERVO AMPLIFIER

HYDRAULIC PUMPS AND CONTROL INTERFACE HYDRAULIC PUMP MOTORS

HYDRAULIC PUMP STARTERS

HYDRAULIC ACTUATORS

VALVES AND PIPEWORK

RUDDERS

RUDDER ANGLE FEEDBACK TRANSMITTER

S G G A



STEERING GEAR

DESIGN REQUIREMENTS

• VARIOUS CONTROL STATIONS

• AVAILABILITY

– LIFE SPAN

– 99.9%

• EMERGENCY OPERATIONS



STEERING GEAR

DESIGN REQUIREMENTS

• LOCKING DEVICE

– HYDRAULIC OR MECHANICAL

• LUBRICATION OF

– Rudder Bearings

– Actuator bearings

steering 01

Documents