Sailed4seas的部落格

Ex 01-05

What awareness ownship can have in this Radar Picture?

After 05 minutes 53 seconds in exercise 01-05,  Let's look at the first part: safe speed.

• Vessel arrive the precautionary area with only 11.5 knots. This means that Ownship  has reduced almost half speed, 19.2 to 11.5 Knots. (Sense) 
• All Crossing traffics (crossing vessels) are not clear yet.  (sense in dead ahead) 
• Ownship collision line (three minutes speed vector line) pointed to port side of "Mobil No.1"  .   (sense) 
• "Mobil No.1"    already altered course to 066 degrees.  (sense) 
• "Mobil No.1"   speed is slower than Ownship.  (skill by compare the length of speed vector.)
• Ownship is in course of 059.7 degrees which is 6 degrees port side to original course. (sense)

After 5 minutes 53 seconds (above), ownship track look quite the same as Ex 01-02 at 5 minutes 24 seconds (below). So, let’s look into these two scenarios and see what happened.

After 05 minutes 24 seconds of in exercise 01-02, Let's look at the first part: safe speed.

• Vessel arrive precautionary area with 10.7 knots. This means that Ownship has reduced almost half speed, 19.2 to 10.7 Knots. (Sense) 
• All Crossing traffics (crossing vessels) are not clear yet.  (sense in dead ahead) 
•  Ownship is in course of 051.9 degrees which is 14 degrees port side to original course. (sense) 

.

Ownship in this Ex 01-05:

• reduced speed twice and in Ex01-02 reduced four times.
• used rudder 4 or 5 times and in Ex 01-02 use rudder twice.
• Used rudder interrupted and in Ex 01-02 decisively.

General speaking:

• Both vessels reduce engine when situation is not clear.( good habit is prudent seamanship)
• Master in Ex 01-05 is not decisive in speed reduction and rudder order. (well, this is not a virtue)
• Master in Ex 01-05 control speed reduction and rudder order randomly with his own hands. (well, this is not a BRM virtue)
• Each time Master in Ex 01-05 feel unsecured, he give rudder order and try to turn some heading he is not sure of. (well, this is lack of collision awareness)
• Each time Master in Ex 01-05 feel unsecured, Master reduced engine output 4 times. (good in collision awareness)
• Master in Ex 01-02 even increased engine output to increase rudder effect when needed. (have correct sense of rudder effect with propeller thrust current)
• With hard over rudder used by Master in Ex 01-02, it surely comes along the risk of “lost control” due to excess turning rate. (sense)
• If master have to control turning rate by himself, it will be a distraction to his collision awareness. (statement)
• Using hard over rudder is correct. Controlling turning rate by master is wrong. (statement)

Correct way to control rudder in narrow strait are:

• Give hard over rudder order first (only to start the turning)
• Wait ownship heading begin to break original course line. (about one minute later)
• Give the heading ownship needed (bearing of target vessel’s stern?) to helmsman to steady. (by rotating EBL to point target vessel’s stern to )
• Adjust ownship heading if needed after helmsman steady on new heading.
• Had helmsman hand steering in narrow strait who can help controlling turning rate. (Very important while traffic are intense because Master is very busy then.

When heading change is over 20 degrees, Master should ask helmsman change heading in two or more steps.

• For example. original course is 066 degree and Master want to change to 090 degrees heading. The procedures will be:
  21. Give “Hard Starboard” rudder order first (only to start the turning)
  21. Wait ownship heading begin to break to starboard side. (about one minute later)
  21. Give the heading 085 degrees ownship needed to helmsman to steady.
  21. Adjust ownship heading to 090 degrees after helmsman steady on new heading 085 degrees.

This 20 degrees stepping heading change is a precaution of “lost heading control” due to excess turning rate. Refer to Zig-Zag test requirement above, we can see:

• Using “Hard over rudder “ over 10 degrees in VLCC and reverse rudder angle to other side, the “First overshoot angle” should not over 20 degrees. Actual sea test result: “First overshoot angle” is 14.3 degrees in VLCC and 5.6 degrees in Container Vessel.
• In here, we can see using “Hard over rudder” through 10 degrees will over shoot 5.6 degrees in Container Vessel and over shoot 14.3 degrees in VLCC.  

When heading change is over 20 degrees, Master should ask helmsman change heading in two or more steps

• Both ownship alter course to port side after 3 minutes 00 seconds exercise time. At the scene it is something like this. (above 01-01-07)
• Ownship have option to alter course to starboard side:
  • Tanker (no.21) on starboard bow is about same speed with ownship. (skill by comparing vector length)
  • Ownship maneuvering will not be a problem with this tanker vessel. (sense with same speed)
  • “Mobil 1” on port bow will pass ownship bow after 3 minutes at present heading. (sense)
  • “Mobil 1” on port bow will be a problem if ownship go to starboard side. (sense)
• Ownship actually can let all three vessels passing our bow after 3 minutes without any problem.(sense by 3 minutes speed vector used)
• Why both ownship worried about collision risks? (confuse comes from using 6 minutes speed vector on Radar)
• Both ownship turned to port side and more close to center separation zone is not a good choice. (against basic concept)
• Both ownship missed window of safety while it opened at 0130 hours. (see the story below)

• Let’s study most confuse time at 0045 hours while two target vessels on both side are crossing. Ownship cannot go anywhere just reduce main engine output and take close visual lookout at these two small vessels. (seamanship)

• Window of safety to correct wrong position of ownship started at 0130 hours. (above)
  • Tanker overtaken at starboard bow are at same speed with ownship now.( sense)
  • Maybe one or two crossing vessels on port side will go east bound like blue line indicated. (sense)
  • Some vessels may alter course to port side earlier and some alter course later.(sense)
  • There will be numerous maneuvering and confuse between these three crossing vessels.

Ownship should alter course to 100 degrees where is the stern of starboard bow overtaken vessel.

• “hand steering please”,
• “hard starboard”
• “hard starboard, Sir” replied by helmsman
• Wait ownship bow begin starboard turn
• “course 080”
• “steady on 080” replied by helmsman
• “hard starboard”
• “hard starboard, Sir” replied by helmsman
• “course 100”
• “steady on 100” replied by helmsman
• “thank you”  “hard port”
• “hard port, Sir”
• Wait ownship bow begin turn to port, “course 080”
• “steady on 080” replied by helmsman
• “hard port”
• “hard port, Sir”
• “course 066” (general direction of traffic flow)
• “steady on 066” replied by helmsman
• “thank you”

End of ex 01-05