Sailed4seas的部落格

Exercise 01-03

Ownship speed vector is in 3 minutes length Collision awareness are

• Own Ship original speed is 19.2 knots.
• Own Ship original course is  066 degree as shown above.
• Ownship is too close to center separation zone and inside deep water route. (sense of danger)
• Starboard side crossing is not a threat after 3 minutes. (sense: she is slower to arrive collision point, passing ownship astern)
• Starboard side crossing will arrive collision point after 5 minutes. (skill: compare blue leg with its three minutes vector.)
• There is 2 minutes difference in arrival time of ownship and target vessel. (seamanship)
• The attention is on port side outbound vessel “Aquarium”which is closer after 3 minutes. (skill)

The seamanship is to look for the way out to starboard side. (outer limits of traffic lane)

• Own Ship keep original speed 19.2 knots.
• If Ownship decide to alter course to  starboard side 085 degree as yellow line above as option 1.
• Why this reading of 085 degrees? (By rotating EBL to the point where target vessel will be after 3 minutes.)
• In this position as yellow ship after 3 minutes to wait starboard side vessel to cross.
• Once again, ownship have a new collision point in orange circle with starboard side overtaken vessel.
• Starboard side overtaken vessel will pass collision point after one minute and ownship will arrive after 2 minutes.
• If ownship arrive collision position as indicated by yellow vessel above, port side crossing vessel will pass ownship bow after 3 minutes.
• By rotating ownship EBL to the direction of overtaken vessel stern direction, we create a new collision point (green circle) with overtaking vessel at our starboard quarter.
• It is better to slow down ownship speed to arrive new collision point (green circle) later.
• How can ownship make the turn to starboard side without collide with overtaking vessel in green circle?
• Ownship alter course now, ownship collision line will cross with overtaken vessel in green circle. This is a sure sign of collision
• It is better to slow down now and find the chance to sail to outer limit of traffic lane later. 

• Is it possible for ownship to do the maneuvering as the drawing above in 3 minutes speed vector?
• The answer is almost impossible to achieve if you are not a very good ship handler.
• 3 minutes speed vector is very hard to turn twice as we had known in vessel’s turning characteristics.
• It is very possible that ownship will alter course as the drawing in the right which is one turn only.

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After 05 minutes 34 seconds of exercise time, At the first part: safe speed.

• Vessel arrive precautionary area with only 11.8 knots now. This means that Ownship  has reduced almost half speed, 19.2 to 11.8 Knots. (Sense) 
• All Crossing traffics (crossing vessels) are not clear yet.  (sense in dead ahead) 
• Ownship collision line (three minutes speed vector line) crossed with "Mobil No.1"   in 2 minutes run.   (sense) 
• "Mobil No.1"    already altered course to 066 degrees same as our original course.  (sense) 
• "Mobil No.1"   speed is slower than Ownship.  (skill by compare the length of speed vector of ownship and target, not in the data area,  but  by eye estimation or with our  finger  span   or  better,  you can prepare a divider beside radar monitor to do the job.)
• If you have good habit always remember the Target Vessel speed, in this case "Mobil No.1"   is 10 knots speed.  Ownship is 1.8 knots faster than her. (sense) 
• Ownship collision risk with “Mobil No.1” is  13 minutes  later.  (  2 minutes run of  11.8 knots is 4 cable. 4 cable  for  1.8  knot run  is 13 minutes  )
• Other crossing vessels are faster than ownship by comparing. (skill by compare the length of speed vector.)
• Ownship is safe with these crossing vessels for speed is slower. (sense)
• Other crossing vessels are safe as long as ownship slower than them.  (statement)
• Ownship further alter course to 060, 6 degrees to portside to give wide sea room for "Mobil No.1".  (this is the trouble when ownship are not in out part of traffic lane) 

 We can check the speed change in the diagram.

• Propeller revolution is in green color which had reduced twice: in beginning and second minutes for safe speed.   (sense)
• Rudder order is in light blue color. Ownship had applied Port rudder at 3-4 minutes time and steady at 5.5 minutes. (suspect) Course change is 6 degrees to port side. (sense)
• Speed is in yellow color. Ownship continue to decrease.  (sense)
• Heading is in red color. 
• Ownship speed decreased slowly to 11.8 knot which postpone collision risk with "Mobil No. 1 "  13 minutes later.   (sense)
• The truth is we don’t know exactly how long ownship had delayed to arrive collision point.
• Ownship still have collision risk after 5 minutes 34 seconds with Mobile No.1.
• Safe speed is hard to achieve with 5 or 6 minutes time.

Let's look at the second part: safe position.

Ownship is nowhere to call in a safe position after 05 minutes 34 seconds of exercise time; Ownship must proceed with caution as they always said.  

End of Ex 01-03