Sailed4seas的部落格

The situational awareness is provided by adjusting Speed vector length to 6 min and 9 minutes presentation. (Skill)

• With three minutes vector length in 21 Knots, this vector is about ten cables distance as above. (skill by knowing  three minutes run)
• Ownship have an overtaking vessel at 6 or 7 cables ahead going to starboard side. (skill by compared this vessel position  in  3 Minutes   vector length)

Three minutes Speed vector length which is our collision line as defined in collision line risk.

Collision Line Risk   is situational awareness when   ownship have to alter course. (Statement)

As the drawing below, ownship use 3 min vector to check collision area risk sweep by ownship collision line. (sighted)

There are 6 vessels will affect by ownship course alternation including the one overtaken ahead.  (sighted)

The reader should try to visualize it as the drawing above.

• After three minutes, the target overtaken (yellow) is very close to ownship. (awareness)
• After six minutes,
  • one target crossing from portside (brown) will pass ownship bow at OS present speed. (Skill by changing speed vector length to 6 minutes )
  • one target crossing from starboard side (purple) will very close to ownship at OS present speed. (Skill by changing speed vector length to 6 minutes )

After 01 minutes exercise time,

• Ownship reduce Engine Output to 28% at first instance. Ship speed reduced from 21.0 to 18.4 knots. (sighted)
• Ownship heading changed from 246.5 to 247.8 degrees. (sighted)

Situational Awareness is :

• the target overtaken (yellow)  is very close to ownship. (awareness)

• After changed speed vector to six minutes,
  • one target  crossing from portside (brown) will pass ownship bow at OS present speed 18.4 Knots . (Skill by changing vector length)
  • one target  crossing from starboard side (purple) will very close to ownship bow at OS present speed. (Skill )
• Reduce Engine Output is effective for crossing; overtaken vessel ahead is still in collision risk.  (awareness)
• Ownship speed is faster than overtaken speed. (skill by comparing the speed vector length of ownship and target vessel)

As a general rule, excess speed is inviting collision risk with overtaken vessel.  

After 02 minutes exercise time,

• Ownship reduce Engine Output to 28% at first instance, increased at 01 minute 20 second then decreased again at 01 minute 40 seconds. Ship speed reduced from 21.0 to 18.4 knots from first minute but no significant change during 01 to 02 minutes. (sighted here to know ownship have no idea of overtaken vessel speed. In another words, ownship have no skill to compare speed vector length to get ownship situational awareness.)
• Engine Output changed twice within this minute are in vain maneuvering due to ownship lacking of necessary skill. (sighted)
• Ownship heading changed from 246.5 to 247.8 to 250 degrees. (sighted)

Situational Awareness is :

• the target overtaken (yellow)  speed slower than ownship. (skill by comparing speed vector length of two ship)
• the target overtaken (yellow) has collision risk with ownship. (awareness)
• and the one overtaken at OS starboard side in inshore traffic lane are altered. (sighted)
• two targets crossing from portside and starboard side will not check again by changing vector length to 6 minutes as ownship already did in first minute. (awareness as ownship speed is almost the same as first minute 18.4 knot.)

After 03 minutes 30 Seconds exercise time,

• Ownship reduce Engine Output to 28% at first instance, increased at 03 minute to 38%. Ship speed reduced from 21.0 to 18.4 to 14.8 knots. (sighted)
• Ownship heading changed from 246.5 to 247.8 to 250 to 236 degrees. (sighted)
• Decisive course change from 250 to 236 degree at 02 minutes with "Hard Port" rudder order over one minute’s interval. (sighted)

Situational Awareness is :

• the target overtaken (yellow),  speed is almost same as ownship. (skill by comparing speed vector length of two ship)
• the target overtaken (yellow) has almost no collision risk with ownship. (awareness)
• the target crossing from portside is no problem as ownship alter course to port. (awareness)
• the target crossing from starboard side will have to check again as ownship changed course to 236 degrees. (awareness )

• After changed speed vector to six minutes,
  • one target  crossing from starboard side will pass ownship bow at OS present speed 14.8 Knots . (Skill by changing vector length)
• New situation arise after course alternation to port side 236 degrees:
  • one ferry boat crossing from port side (yellow circle) is end on with very small margin at three minutes run. (awareness)
  • one vessel overtaking from port quarter (Pink circle ) will at ownship stern at three minutes run. (sighted)
  • Right now, if ownship further reduce Engine Output will narrow the distance with Pink circle overtaking vessel. (awareness)

After 05 minutes 00 Seconds exercise time,

• Ownship reduce Engine Output to 28% at first instance, increased at 04 minute 20 seconds to 90%. Ship speed reduced from 21.0 to 18.4 to 14.8  and increased to 19.3 knots at 05 minutes. (sighted)
• Ownship heading changed from 246.5 to 247.8 to 250 to 236 degrees, course steady at 236 degrees. (sighted)
• Decisive speed change from 14.8 to 19.3 knots at 03 minutes 30 seconds with "90%" Engine Output. (sighted)

Situational Awareness is :

• the target overtaken (yellow)  is irrelevant,  has almost no collision risk. (awareness)
• one ferry boat crossing from port side had altered course to portside crossing the separation scheme at right angle. (sighted)
• As a general rule, vessel crossing seperation area or separation  line may alter course abruptly .  
• the target crossing from starboard side will have collision risk as the collision point and collision line are almost coincided. (awareness )

This new situation is the result of lacking necessary skill:

• Course to 236 degrees is OK. (suspect)
• Ownship increased Engine Output to 90% to avoid the overtaking vessel from port side (Pink circle) is not OK. (suspect)
• Ownship have better solution if ownship keep original speed of 14.8 knot and alter course to starboard side 246 degree.  (skill by imagination)

The reason for this recommendation are based on two concept :

1. Excess speed always means trouble as in this case increase speed to invite more collision risk like the red speed vector of 19.3 Knots.
2. As a general rule, Keep same course with target vessel is relative safe regardless Ownship’s speed.  (Image ownship sail in parallel track with target vessel like two railway track.)

After 06 minutes 30 Seconds exercise time,

• Ownship reduce Engine Output to 28% at first instance, increased at 04 minute 20 seconds to 90%. Ship speed reduced from 21.0 to 18.4 to 14.8  and increased to 19.3 knots at 05 minutes. At this time, ownship speed is 18.5 knots with engine output 23% only.  (sighted)
• Ownship heading changed from 246.5 to 247.8 to 250 to 236 to 250 degrees, course steady at 250 degrees. (sighted)

Situational Awareness is :

• the target overtaken (yellow)   is abeam of ownship has almost no collision risk. (awareness)
• one ferry boat crossing from port side had altered course to portside crossing the separation scheme at right angle. (sighted)+
• Decisive course change from 236 to 250 degrees at 05 minutes 00 seconds had paralleled overtaking vessel from port quarter. (sighted with same course)
• However this course alternation from 236 to 250 degree is good enough for overtaking vessel, but not good enough for the crossing vessel from starboard side. (Sighted  have collision risk as the collision point and collision line are almost coincided.)
• This practice reflects one popular myth To alter course 15 degrees first, see what happen next? (sighted )
• Course alternation from 236 to 256 degree, at least 20 degrees from 05 minute 00 second, will be good enough for overtaking vessel and for the crossing vessel from starboard side. (Skill by knowing how many degrees is needed at how many distance away? Please refer to appendix in the end.)
• If you don't believe, please refer to the final result in Ex time 07 minute 55 minutes.

After 07 minutes 55 Seconds exercise time,

• Ownship reduce Engine Output to 0% now, increased at 04 minute 20 seconds to 90%. Ship speed reduced from 21.0 to 18.4 to 14.8 and increased to 19.3 knots at 05 minutes. At 06 minutes 30 Seconds, ownship speed is 18.5 knots. At 07 minutes 55 Seconds, ownship speed is 17.6 now. (sighted)
• Engine output variation during these 8 minutes is represented as the lowest green line on the diagram above, it like a wave. (sighted)
• Ownship heading changed from 246.5 to 247.8 to 250 to 236 to 250 to 260.4 degrees, Ownship use "Hard Port" rudder to steady on 260 degrees. (sighted)

Situational Awareness is :

• Vessel turning from 06 minutes with "Hard Starboard" rudder and "Midship" at 06 minutes 30 seconds. Ownship did not stop turning to starboard side.  At 07 minute, ownship try to steady on the course of 260 degrees with "Hard Port". (sighted) 
• The light blue line on the diagram is the rudder angle used in maneuvering. Light blue line on the upper area represent as "port side rudder" and on the lower area represents "Starboard side" rudder.
• From the diagram, ownship will notice ownship track mostly turn to starboard side but rudder angle were mostly used at  port side. (sighted)
• Ownship has the tendency to turn to starboard side easily and hard to go to port side. Please compare the track of rudder angle at 06 minutes is "starboard 15" for 20 second only and ownship use "Port 20" for 40 second at 07 minutes. Still, OOW cannot stop the turn to starboard side which started at 06 minutes. (sighted, this is act of mother nature by wind or current.)
• Rudder angle used in prolonged period (20 seconds, 40 seconds) is a sure sign of ownship confidence on his ship handling skill. (skill)
• Engine output varied frequently is a sure sign of lack understanding of ownship speed performance. (suspect)
• Why ownship have to alter course at least 20 degrees at one nautical Mile distance away? 

Appendix: 

From the situation at 05 minutes 00 Seconds exercise time,

• Ownship speed is 19.3 knots. We use 20 knots for easy calculation.
• Ownship 3 minutes speed vector length is about one nautical Miles by 20 knots speed.
• The collision point risk is as shown above at end of three minutes speed vector and somewhere inside the while circle of 600 Meters in diameters.

To avoid this collision circle of 600 meters diameter is base on the assumption of  

• Target vessel length 300 meters long as semi-diameter.
• Collision could happen on target vessel stern if Target passed the collision point earlier. 
• Collision could happen on target vessel bow if ownship passed the collision point earlier .
• Collision Avoidance is to keep clear of the collision point, not to keep clear of other vessel. 
• This 600 beam distance is to keep clear of the collision point.
• Whenever we need to do collision avoidance maneuvering, one thing must be sure of “To know where the collision point is we had in mind?".
• In open sea, OOW can concentrate on avoid the vessel for the sea room is plenty.
• In narrow channel, give wide berth to every vessel is impossible.
• Ownship have to give just enough sea room (600 meters for instance) will be OK.
• The reason why will demonstrate on the Exercise to come in this series.

θ(Course Change) =SIN^-1 600 Meters (Ship's Length x 2)/ (1852 Meters x ？Nautical Miles (Distance)  )

• θ= 1.5 degree  = SIN^-1 600 m / (1852 m x 12 NM )  (Distance to other ship  = 12 NM，course change =1.5  degree)
• θ= 3.0  degree = SIN^-1 600 m / (1852 m x  6 NM )  (Distance to other ship  = 6 NM，course change =3.0  degree)
• θ=4.6  degree = SIN^-1 600 m / (1852 m x  4 NM )  (Distance to other ship  = 4 NM，course change =4.6  degree)
• θ=6.2  degree = SIN^-1 600 m / (1852 m x  3 NM )  (Distance to other ship  = 3 NM，course change =6.2  degree)
• θ=9.3  degree = SIN^-1 600 m / (1852 m x  2 NM )  (Distance to other ship  = 2 NM，course change =9.3  degree)
• θ=19  degree = SIN^-1 600 m / (1852 m x   1 NM )  (Distance to other ship  = 1 NM，course change =19  degree)

For easy memory, the general rule for Course Change   in different distance to avoid collsion point  are simplified as

• (Distance to other ship  = 6 NM，course change =3.0  degree)
•  (Distance to other ship  = 4 NM，course change =5  degree)
• (Distance to other ship  = 3 NM，course change =6  degree)
•  (Distance to other ship  = 2 NM，course change =10  degree)
• (Distance to other ship  = 1 NM，course change =20  degree)

End of Exercise 02-02