Sailed4seas的部落格

Collision Awareness Exercise – 01 Safe Position

Ex 01-01-01

Concept of Collision Point:  The point where two vessel course lines crossed each other.

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By the drawing: ownship speed vector is in 6 minutes length, there are three collision points (in yellow circle), Collision awareness are

•  Collision point of Starboard side fishing Vessel has shortest distance to Own Ship. (sense)
• But, this is misleading. (suspect)
• 6 minutes speed vector serves to know potential collision risk after 6 minutes. (statement)
• Two vessels have collision point did not mean they have collision risk. Collision has another criterion to actually happen. (suspect)

Real collision consisted of two parts: two vessels arrive at same place and same time.

If we display the actual ship shape on the drawing, Collision awareness are

• Ownship can notice immediately that third vessel is closer to Own Ship after 6 minutes. (sense)
• Although fishing vessel 10 on starboard side has the closest collision point No.1, (sense)
• Fishing vessel 10 arrive the collision point at about 5 minutes later. OS pass No. 1 collision point at about 3 minutes. (sense)
• Ownship and No.10 Fishing Vessel did not arrive No,1 collision point at same time. There will be no collision for ownship and NO.10 FV. (statement)
• From this picture, it is hard to say these two vessels on portside which have collision point No.2 and No.3 are arrive at same time with Own ship or not. (suspect)

If the end of two vessels speed vectors close to each other then these two vessels has collision risk.  (rule)

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In here,  speed vector is in 3 minutes interval which Collision awareness are

• No.10 FV is a not threat to OS after three minutes. OS can pass ahead of it 2 minutes earlier. (sense)
• No.20 “Aquarium” on port side will arrive collision square after 3 minutes (red square where two vessels movement are uncertain). (sense)
• No.13 “Mobil  1”on port side is not certain?  (suspect)
• The precaution area is in red square and ETA to there is 3 Minutes. (statement)

We should have the imagination to see The position in each end of these speed vectors will be a vessel there after three minutes.(just like the picture below)

​No. 20 vessel is outbound from harbour limit, what will be his possible course after that? The Collision awareness are:

• This vessel outbound bur her heading is not the same as other outbound vessels. (sense)
  • This heading suggests this vessel is more likely to go westbound and turn to starboard side 245 degrees. (suspect)
  • If she want to go eastbound  065 degrees, she may alter course to 065 degrees just after crossing separation line in the red sphere area .(suspect)
  • This red sphere area is the trouble water as other traffic vessels may alter course in any time closer by there. (suspect)
  • She also may cross traffic scheme in her current heading now. (suspect) 
• Crossing or not, depends on her service route. We have to wait and see (sense)
  • Is she a working or supply ship around port area then every direction is possible (suspect)
  • If She is an ocean going vessel who want to join traffic lane to westbound or eastbound
    ? (suspect)
  • Often, VTS will make announcement of outbound vessel name. (suspect)
  • or ownship should keep radio watch of VTS VHF channel. (statement)
• The best choice for Own Ship now is to reduce speed and let her pass ahead( fulfill the "safe speed" in COLREG, suspect)
• If target vessel wants to go eastbound and join Ownship’s traffic lane, Ownship may need to shift starboard to give more sea room for her to turn. (suspect)

• After 45 seconds exercise time (in yellow circle), this vessel "Aquarium" is in collision risk with Own Ship. (sense)
• Alter course to starboard side may cause another collision risk with fishing boat No. 10. (sense)
• But "Aquarium" is still inside the harbour limit (sense)
• Check target vessel position in harbour area can have better understanding of her maneuvering. (statement)
• Visual checking target vessel maneuvering by looking out of ownship window is prudent seamanship.
• She is give-way vessel from port side, ownship should wait longer although "Aquarium" has only 9 cable away. (suspect)
• Or we should further reduce speed (for OS now is making 17.7 knots) (sense)
• Alter course to starboard side to give more sea room for outbound vessel is not a good choice for NO. 10 vessels on starboard side with closer range. (sense)
• Steady on ownship current heading is good if "Aquarium" go westbound traffic lane. (SENSE)
• Steady on ownship current heading is good if "Aquarium" cross separation line and immediately go eastbound direction. (sense)
• Steady on ownship current heading is not good if "Aquarium" cross separation line and do not immediately go eastbound direction. (sense).

At 01 min 30 seconds Exercise time, Collision awareness is

• Starboard side fishing vessel No. 10 is circling around to east and irrelevant now. (sense)
• "Aquarium" alter course to starboard side. (sense)
• "Aquarium" is going westbound or go astern of Own Ship? (suspect)
• Own ship should pay attention to other outbound vessel too. (statement)
• Now which outbound vessels are  more likely going eastbound, not crossing. (skill: by check outbound vessel size and type)
• Own ship had reduced speed to 16.3 Knots now. Originally OS has 19.2 Knots at 90 seconds before.(sense)
• Now should ownship further reduce speed or just wait and see.  (suspect)

At 02 min 30 seconds Exercise time, Collision awareness are

• Port side working vessel No. 13 will pass Own Ship bow after three minutes. (sense)
• "Aquarium" alter course to starboard side and  go astern of Ownship. (sense)
• Port side CTNR vessel No. 18 can clear Own Ship bow after three minutes. (sense very easy in 3 minutes vector, but very hard to tell in 6 minutes vector if you try)
• Own ship had reduced the speed to 14.6  Knots now. Originally OS has 19.2 Knots at 02 min 30 seconds before. (sense)
• Now ownship can sail with this safe speed 14.6 knot till all crossing vessel clear OS bow.  (suspect)

At 03 min Exercise time, Collision awareness are

• Port side Working vessel No. 13 can clear Own Ship bow after 2 minutes. (sense)
• Port side CTNR vessel No. 18 can clear Own Ship bow after three minutes. (sense)
• The fast No.11 Pilot  boat  can clear Own Ship bow after three minutes. (sense)
• Own ship had reduced speed to 13.9  Knots now. Originally OS has 19.2 Knots at 3 min before. (sense)
• The speed difference is 5.3 knots in three minutes. This speed reduction is important.(sense)
• "Aquarium" alter course to starboard side  and go westbound. (sense)
• Now we can sail in this speed 13.9 knot till all crossing vessel clear OS bow.  (it is easy to check 3 minutes vector on RADAR, if ownship using 6 minutes speed vector to check collision points will be very hard to tell immediately)

While everybody happy now, we will further study on this scenario.

• The speed vector involved with collision risk. (statement)
• If we reset Own Ship speed to original 19.2 Knots, the speed vector of 3 minutes will be 8.6 cables longer on than current speed 13.9 knots, speed vector of 3 minutes will be 6.9 cables. (sense as Radar picture above)
• Port side Working vessel No. 13 and  Port side CTNR vessel No. 18 will have collision risk with ownship. (sense)
• We can not sail with speed 19.2 knot to  clear all vessels after three minutes. (sense with red ship’s position will have collision risk with these two vessels)
• All crossing vessels will become nightmare to us after three minutes. (sense)
• We can sail in green vessel with speed 13.9 knot safely till all crossing vessel clear OS bow? (for sure)
• More speed in ownship will have more collision risk involved. (statement)
• Any uncertainty in collision situation, stop the engine immediately to get more time to evaluate the situation and postpone collision time if any. (statement)
• While all ships seem working together to against you, just reduce ownship speed to minimum as quickly as possible. (statement)  
• Collision risk is proportional to ownship speed. (truth)
• No Speed, No collision risk involved. (almost) 

At 04 min 30 sec Exercise time, Collision awareness are

• All Port side vessels will clear Own Ship bow after 2 minutes. (suspect)
• Own ship had reduced speed to 12.2  Knots now. Originally OS has 19.2 Knots at beginning. (sense)
• 3 minutes speed vector show ownship will arrive collision square after 3 minutes. (skill)
• "Aquarium" had passed. (sense)
• With the radar speed vector picture ensured our safety in mind, we can concentrate on our visual techniques now to make sure
  • Crossing vessel bearing change (True or  relative bearing) from port side to starboard side  till all clear OS bow.  (suspect)
  • Crossing vessel heading change to their port side, if it is an eastbound vessel? (suspect)
  • Crossing vessel heading had not changed, if they continue current heading. (suspect)

End of Ex 01-01