Sailed4seas的部落格

Ex 05-05

Ownship speed is 20.0 Knots and course is 245.4 degrees at beginning. 
The situational awareness is:
•    With three minutes vector length in 20.0 Knots, this vector is about 10 cables distance as above. (skill by knowing  three minutes run)
•    Ownship have two crossing vessel at starboard side (red circle), distance unknown. (sighted)
•    One overtaken vessel at starboard side has slower speed. (skill by comparing vector length)
•    Ownship have one crossing vessel at port side (green circle), distance unknown. (sighted)
•    Two overtaken vessels at port side slower than ownship. (skill by comparing vector length)
 
The situational awareness with 6 minutes speed vector is:
•    There are 6 vessels inside the collision square (Orange square). (sighted)
•    There is no time to remember what vessel is ahead or behind, what vessel is on starboard side or port side? (suspect)
•    Ownship now knows that “It is Collision area to be avoided, not the vessels”(statement) 
•    Where to go for ownship? (suspect)
•    To starboard side, One port side crossing vessel (green circle) will be at ownship starboard bow after 6 minutes which block ownship way to starboard side. ( sighted) 
•    To port side, two starboard side crossing vessel (red circle) will be at ownship bow after 6 minutes which will block ownship way to port side. ( sighted)
•    To make a 360 degrees turn, many vessels inside the traffic lane. (sighted) 
•    Ownship has the option to reduce speed as fast as possible to arrive collision square later. (suspect)
 
After 3 minutes 00 seconds exercise time lapsed:
Ownship speed is 14.3 knots which decreased from 20.0 kts with engine output reduced to 55% from beginning. 
Ownship course had altered 4 degrees starboard side to 248.8 degrees from 245.4 degrees with rudder ”starboard 10”longer and “Hard Port” shortly in last 3 minutes. 
The situational awareness in 3 minutes speed vector is:
•    Ownship reduced speed is not decisively. (sighted)
•    Speed reduces 5.7 knots over 3.0 minute’s time. (sighted with reducing rate of 1.9 knots per minutes)

• For all crossing vessel will pass after 3 minutes are the effect of heading change 4 degrees starboard side to 248.8 degrees from 245.4 degrees. (sighted)
• In this exercise, ownship suffer a lot of “OK” then “ not OK” situation are the demonstration of “ How ship’s heading are so important while the traffic is heavy. (statement)
• Ownship looks Ok with all crossing vessels but have problem with overtaking vessel on starboard quarter which is faster than ownship now. (sighted)  
    

After 5 minutes 00 seconds exercise time lapsed:
Ownship speed is 16.0 knots which increased from 14.3 knots 2 minutes ago with engine output increase to 100%. 
Ownship course had altered 1.5 degrees port side to 247.3 degrees from 248.8,  245.4 degrees with rudder “Hard starboard “shortly then “starboard 10” in last minute. 
The situational awareness in 3 minutes speed vector is:
•    Right now ownship has vessels on port and starboard bow.(sighted)

• In last minute ownship tried to alter course to starboard side with Starboard rudder and full ahead engine output with 100%. (sighted)
• Now ownship knows one minute time is not enough for a vessel to turn. (statement)
• Ownship course had changed 1.5 degree to port side and increased engine to avoid overtaking vessel.(sighted)
• Although the situation looks complicated ownship had two crossing vessel about to pass after one minutes. (sighted)

Sudden engine output increased may not be a good idea. (suspect)

After 6 minutes 54 seconds exercise time lapsed:
Ownship speed is 21.8 knots which increased from 16.0 knots 2 minutes ago with engine output increase to 100%. 
Ownship course had altered 4.8 degrees starboard side to 252.1 degrees from 247.3, 248.8,  245.4 degrees with rudder effect carry over 2 minutes ago. 
The situational awareness in 3 minutes speed vector is:
•   Vessels crossing from port and starboard side are cleared now.(sighted)

• Two crossing vessels from port side will pass ownship stern after 3 minutes. (skill)
• Ownship altered course to starboard side 4.8 degree and full ahead engine output with 100%. (sighted)
• Ownship used “Port 10” rudder to control vessel turning. (sighted)
• Ownship course steady on 252 degree to avoid overtaking vessel.(sighted)
• Ownship speed is faster than overtaking vessel now. (skill)
• Sudden engine output increased may not be a good idea. (suspect)
   

The moral of this exercise is:
 

• Small course alternation is not recommended for collision avoidance in COLREG.
• In dense traffic, ownship any sudden course alternation is dangerous to all parties at scene.
• The only option left for ownship to avoid collision is to reduce engine, and reduce it effectively.

• 6 minutes speed vector for any one is a mess like the one above.
• 3 minutes speed vector had made allowance for vessel’s turning characteristics.
• To keep 3 minutes speed vector or collision line in Radar display clear of any vessel is the base line for safety.
• Collision point in 6 minutes speed vector is a warning of collision risk.
• Collision point in 3 minutes speed vector is a sure sign of collision risk.

• All crossing vessels is about to pass after 3 minutes as above. (skill by ownship knowledge)
• Ownship will arrive collision square after 5 minutes. (make sense of this statement)
• Ownship have 2 minute time lapse to collision point. (obvious)
• Only thing ownship have to do now is to adjust course to port side slowly. (suspect for vessel ahead)
• Course alternation 5 degrees to port for overtaking vessel will be enough. (suspect or skill by experience)
• Remember once ownship had known 10 degrees is necessary for collision avoidance in 2 Nautical Miles. (statement)
• There are different concepts in collision avoidance
• In open sea: 10 degrees is necessary to avoid target vessel which has real collision risk. (to avoid target)
• In dense traffic: 5 degrees is necessary to avoid collision which is inside collision square. (to give sea room)

End od Ex 05-05