Crown PrincessCrown Princess

Vessel Dynamics

Overview

• Ship dynamics under INS

• 2nd officer’s manual inputs

• Two opposing heeling responses

• Lag between wheel input and rudder/ship response

• Motion cues

Primary Motion

• Yaw Axis

– Heading– Turn rate– Turn acceleration

• Roll Axis

– Heel angle– Heel rate– Heel acceleration

Recorded Motion

15:05:00 15:10:00 15:15:00 15:20:00 15:25:00 15:30:0030

25

20

15

10

5

0

-5

-10

-15

-20

-25

-30

Starboard

PortT

urn

Ra

te (

de

g/m

in)

Local Time (hr:min:sec)

Turn rate

Manual Steering Begins

15:05:00 15:10:00 15:15:00 15:20:00 15:25:00 15:30:0030

25

20

15

10

5

0

-5

-10

-15

-20

-25

-30

40

30

20

10

0

-10

-20

-30

-40

Starboard

Tu

rn R

ate

(d

eg

/min

)

Local Time (hr:min:sec)

Turn rate

Port

Ru

dd

er

& H

ee

l An

gle

(d

eg

)

Heel angle

Port

Starboard

Manual Steering Begins

15:05:00 15:10:00 15:15:00 15:20:00 15:25:00 15:30:0030

25

20

15

10

5

0

-5

-10

-15

-20

-25

-30

40

30

20

10

0

-10

-20

-30

-40

Starboard

Tu

rn R

ate

(d

eg

/min

)

Local Time (hr:min:sec)

Turn rate

Port

Ru

dd

er

& H

ee

l An

gle

(d

eg

)

Heel angle Rudder command

Port

Starboard

Manual Steering Begins

Turning a ship

• Wheel command to rudder

Rudder force

Rudder force

Rudder force

Rudder force

Ship’s Response to Rudder

Direct Rudder Heeling Moment

Direct Rudder Heeling Moment

Response Lag

• Direct rudder effect

– Immediate heel response to rudder

• Sideslip effect

– Ship must first yaw in response to rudder

– Takes longer– Much stronger

Saturated Rudder

15:24:00 15:24:15 15:24:30 15:24:45 15:25:00 15:25:1530

20

10

0

-10

-20

-30

-40

-50

Starboard

Rud

der

(de

g)

Time (hr:min:sec)

Rudder command Rudder response

Port

42 sec

Manual Steering

Motion Cues

• Positive correlation with:

– Heel angular acceleration– Heel rate

Summary

• The 2nd officer’s commanded rudder changes faster than the rudder could respond

– During a 30 deg starboard rudder command the rudder actually port

Summary (cont.)

• Two effects of rudder on heel

– Short term direct response in direction of rudder input

– Longer term more powerful sideslip effect in opposite direction

Summary (cont.)

• Rudder commands modulated heel rate (while turn rate continued to increase)

– Port rudder initially slowed starboard heel rate

– But at longer term expense of increased starboard sideslip

• Starboard sideslip overwhelmed direct rudder effect producing starboard heel

Summary (cont.)

• Opposing long term and short term effects complicate the 2nd officer’s efforts to control the heel