Sailed4seas的部落格

Ex Illus. 01-01

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Now, let's take a look of the collision definition. Two targets arrived at same place at same time, just like the illustration above. We define 

• Collision Point Risk: The point of two ships course line crossing each other.
• Collision Line Risk:  The line of two Ships 3 minutes speed vector crossing each other.
• Collision Square Risk: The Square of many ship speed vectors overlapping each other.

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• Collision Point Risk: The point of two vessels course line crossing each other which is the Yellow circle in above diagram.
• Collision Line Risk:  The line of two Ship speed 3 minutes vector crossing each other like the vessel with Green dotted speed vector.
• Collision square Risk: The square of many ship collision line s crossed and overlapped area which may cover by Own Ship maneuvering.

The concept of Collision Point Risk:  Raise the Collision awareness of possible crossing situation.

• Collision Point may be many in Harbor area. (statement is something in general)
• Not all collision points have collision risk. (statement)
• Only those points Own Ship arrived at same time with other has collision risk. (statement)
• Collision Point raises the Collision awareness of possible crossing situation in voyage and sailing route planning. (skill is something we do it on purpose to ensure our safety )
• If we are looking for collision risk, we should concentrate on the end of speed vector. (skill)
• The end of speed vector is the vessel’s position after specified minutes later. (statement)
• In this picture, Only No.1 collision point did not have collision risk for Ownship will pass starboard side crossing vessel bow after 3 minutes.  (skill by judging the ship’s position on ARPA after 3 minutes)
• Or starboard side crossing vessel will pass Ownship stern after 5 minutes. (skill by judging the ship’s position on ARPA after 6 minutes)
• No.2 and No. 3 collision point involved collision risk are not very sure now. (sense is something uncertain)
• No.2 and No. 3 collision risk may be verified by using shorter speed vector of three minutes. (skill)

The concept of Collision Line Risk:  Raise the Collision awareness of Ownship when turning is required by ownship or target vessel.

With 3 minutes speed vector length on APAR screen, collisions Awareness are:

• No.1 vessel is slower than ownship to arrive collision point: Own Ship will pass her bow. (sense)
• Green circle covered by No. 1 vessel is the area where No.1 vessel may be in three minutes. (statement)
• No matter what direction No. 1 vessel sailed, she won’t collide Ownship within three minutes. (statement)
• The collision line (3 minutes speed vector) did not cross between Own Ship and No. 1 Target; there is no collision risk with no.1 target in these three minutes. (sense)
• If collision lines (3 minutes speed vector) had not crossed, there is no collision risk.
• No.2 vessel arrive red collision circle almost same time with Own Ship. (skill)
• If two vessels Collision line crossed there will have a collision risk involved. (sense)
• Two vessels 6 minutes speed vector crossed there does not mean collision risk will be involved. (skill : is something need some kind of knowledge to aware and to do something to verify its results)
• Using different speed vector length to get collision awareness as needed. (seamanship)
• Usually, two vessels have collision point in speed vector end area within 3 minutes difference means collision risk. (check below left picture of 14:58:17 hours where the speed vector is in 3 minutes length)
• In the center picture of 14:59:37 hours: where collision point to westbound vessel is about 2 minutes time(01:37 hours) and to south bound vessel is about one minutes time(00:37 hours). The collision time has one minute difference but collision happened due to vessel’s length and turning ability is restricted. (wrong sense of safety which did not take account of human mistake and vessel’s dimensions into consideration )
• In the right picture of 15:01:07 hours: Two vessels collided which is not the time we read from ARPA picture 01:37 hours or 00:37 hours. (sensed)
• South bound vessel altered course from 134 degrees to 151 degrees, course alternation not only changed ownship’s position in collision but also have effect on delaying ownship speed and passing time. (this needs full details in following chapter) 
• collision lines is 3 minutes speed vector to keep enough maneuvering room for both vessels
• While conducting avoidance maneuvering, make sure 2 things:
  • Make every effort to avoid Speed vector in 3 minutes length crossed with other vessel in advance to allow for enough time for both vessels to pass each other with wide berth. (ownship can make sure of collision risk if seeing 3 minutes speed vector is about to cross after 6 minutes or 9 minutes before collision risk happened)
  • Change Speed vector in 3 minutes or 6 minutes or 9 minutes length…… alternately can give ownship more specified picture of collision awareness. (ownship may overlook the collision risk more than 3 minutes if only set to 3 minutes only )

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The illustration above is an actual case which can demonstrates collision line concept is correct and collision awareness can be more certain by this way.

(http://sailed4seas.pixnet.net/blog/post/174800927-VLCC%20collided%20with%20VLCS%20at%20Singapore%20Strait)

Collision square is the Orange Square on picture below where 7 vessels will arrive at same time in same place.  (any ship’s movement is immediately interacted with other vessels near by, every ship could be giveway vessel and stand on vessel at the same time)

• Collision Square is the areas ownship should make allowance for other vessels maneuvering and dimensions into collision consideration. (seamanship)
• Collision Square is the areas where no guidance had provided before to prepare our seaman venture. (seamanship)
• Collision Square is the areas where ownship have to know the reasons why collision happened this way. (Seamanship: to understand the case above just mentioned collision predicted different from ARPA and actual case. )

Three minutes speed vector cover the distance of 3/60 (one twentieth) of ship's speed. The drawing below is for faster container  vessel use. Faster container  vessel(C/V) different from slower tanker vessel (VLCC) in two ways:

Courses maintain ability:   Faster speed Container  Vessel tend to stick on her original course longer, slower speed VLCC vessel can start the turn more quickly.  (Statement)

Turning stop ability:  Once start turning, faster speed Container  Vessel can stop the turn more quickly than  slower speed VLCC vessel.  (Statement)

• For a 20 knots container vessel,  3 minutes speed vector represent One Nautical Mile distance run. (statement)
• One Nautical Mile is 1852 meters which is 6.2 times of ship's length of Panamax vessel at 295 Meter ship's length. (statement)
• This  6.2 times of ship's length advance distance is needed for Own Ship to make course alteration to be effective.
• This advance distance of 3 minutes is essential for Ownship Shiphandling Safety. (statement)
• For a 12  knots VLCC vessel,  3 minutes speed vector represent 0.6 Nautical Mile distance run. (statement)
• 0.6 Mile is 1111.2  meters which is 6.9 times of a small ship's length at 160 Meter. (statement)
• Faster panamax vessel has faster speed 20 knots than 160 meter small vessel in 12 knots. (as calculated)
• Roughly speaking: 3 minutes speed vector can cover ownship and target vessel maneuvering requirement of 6 ship’s length. (This is an assumption)
• Small vessels in slow speed three minutes run (1111.2 meters) can have more times of ship's length (6.9 times) than Panamax vessel (6.2 times). (statement)
• Roughly speaking: Small vessels are easier to maneuver than Panamax vessel. (statement)
• Because Small vessel had not reached her limits of maneuvering, that's why Panamax vessels are more anxious than Small Vessel and have to take action earlier while crossing or in collision Avoidance. (seamanship)

Please refer to turning characteristics above,  

1. Origin ship position is white ship.
2. Point of origin is on Own Ship Bridge.
3. Green ship represents the end of first stage of turning where ship bow just leave original course line.
4. Blue ship represents the end of second stage of turning where ship stern just leave original course line.
5. Purple ship represent the end of third stage of turning where ship bow and stern clear original course line with beam distance of one ship length.
6. The black curved track represent different rudder angle had been used which are 5^0, 10^0, 20^0,30⁰ to port side and starboard side.
7. If ownship length is 230 meters; two ship's length is about 0.25 NM as the drawing above.

We have some observations to note on ship’s turning characteristics:

• In first two ship length advance stage (0.25 NM), Own Ship is helpless in collision risk. No matter what rudder order (5^0, 10^0, 20^0,30⁰ to port or starboard side) had applied is useless. Vessels just collide with anything ahead with his bow. Own Ship can only hope for reducing the collision momentum by crash astern (if reverse propeller rotation can be established within 60 seconds. By IMO resolutions below, this 60 seconds is hopeless to get reversed propeller rotation).

• In second stage of four ship length advance (0.25 - 0.5 NM), Own Ship bow can clear original course line, but ship stern had not leave original course line yet. More rudder order (5^0, 10^0, 20^0,30⁰ to port or starboard side), more quickness ownship bow may deviate from original course line. Vessels just collide with her stern in this stage.
• In third stage of six ship length advance (0.5 - 0.75 NM), Own Ship body can clear original course line, but beam distance might not enough. More rudder order (5^0, 10^0, 20^0,30⁰ to port or starboard side), more quick ship body deviate from original course line.

Next time, you saw maritime news one ship collide in his bow it is very possible that this vessel used rudder in last minute (which is Titanic case). If this vessel collide in his stern it is very possible that this vessel used rudder 2 minutes before collision (which is Costa Concordia case). 

Sadly to say, vessel collision in third range is basically Human Error. In third stage ownship had deviated from original course line. It means ownship had deviated from original collision point like the yellow circle above (remember collision point is in original course line). If collisions happen outside ownship course line, collision points will be like those green circles above. If you have correct collision awareness, these collisions won’t happen. It will be a long story to say. Take close look at the picture of collision where I always marked collision point with a circle or square. For now, just look at the drawing above with dotted yellow tracks by different rudder angle been used.

1. New collision point is green circle after Own Ship turn to port side or Target Vessel turn to starboard side.
2. These green circles are not coinciding with original yellow circle Collision Point.
3. In another word, one of these two vessels must have made wrong turn to collide in these green circle spots.

The reasons of these kinds of Miss Maneuverings are imbedded in long time concept:

To avoid collision is to avoid target vessels.  We concentrated on target vessel movements in collision avoidance maneuvering for not knowing what to do.

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The concept of Collision Awareness in three stages:  

• Collision Point Awareness: To aware of the point of two ships course line crossing each other.
• Collision Line Awareness: To aware of the line of two Ships 3 minutes speed vector crossing each other.
• Collision Square Awareness: To aware of the Square of many ship speed vectors overlapping each other.
• Collision Point Awareness is the collision awareness ownship required in voyage or course planning many days before sailing or need course alternation.
• Collision Line Awareness is the collision awareness ownship required in collision avoidance at scene.
• Collision Square Awareness is the collision awareness ownship required in narrow strait or dense traffic area to meet complicated situations.
• After course changed, ownship heading line will sweep over an area of   three minutes distance run.  (statement of collision line concept)
• What headings other vessels will sail inside these Collision squares are hard to decide. (statement)
• In close quarter situation, it is more important to realize it is   a Port Side Danger or a Starboard Side Danger.  (skill)
• In this 3 minutes speed vector touched situation, ownship had only one chance to make ownship sail to right side(sense)
• In the case above, Northern Jasper alter course to west (port side) and Safmarine Meru try to out run it to more westward. (statement)
• The collision happened.  Don’t go to the side Target Vessel had started to go in close quarter situation especially if 3 minutes vector collision line had already crossed (or already touched).   (suspect)
• In this 3 minute situation, ownship has only one chance to make ownship sail to right side(sense)
• Nothing to Port or Nothing to Starboard as a river pilot did to make sure ownship stay in safe side. (seamanship)
• There is another simple truth that ownship cannot complete a 360 degrees turn within 3 minutes. (sense)
• If 3 minutes speed vector collision line crossed, ownship have only one chance to alter course and only one side to sail. (Seamanship).
• If target vessel had gone to wrong direction in close quarter situation, ownship should try to do rudder cycling with “Hard Over” rudder. (seamanship needed to develop in following chapters )
• Two cases, ownship should alter course to target as below pictures. 
  • If target vessel relative bearing changes are to pass own ship bow,
    • Ownship will hit target vessel stern or Midship section.
  • If target vessel relative bearing changes are to pass own ship stern,
    • Target vessel will hit ownship Midship section or stern.

If you want to know who the victim is during the collision, you can check on relative bearing of target vessel’s bow (red line). (Seamanship in other tougher assays.)

Roughly speaking now,

• Collision risk is decided by relative bearing of target vessel’s stern(in both case, target vessel’s stern relative bearing is almost unchanged.)
• Victim is decided by relative bearing of target vessel’s bow:
  • in case target vessel’s bow relative bearing changed quickly, he will be the victim .
  • in case target vessel’s bow relative bearing changed slowly, ownship will be the victim .

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