Using Speed Vectors to Detect Risk:

Speed vectors serve as a "collision line" for quick assessment. Refer back to Figure 2-15 (from the previous chapter): No matter the time length set for the speed vector, the last 3 minutes of a true-motion speed vectorrepresents your physical limitation in turning—the part that is unavoidable in collision avoidance. That means even the most experienced master or pilot must obey this simple physical rule. Collision risk cannot be handled or avoided within the last 3 minutes. Extending speed vectors to more than 3 minutes (or longer) to probe proper collision avoidance action timing is seamanship. In Figure 2-14 (6-Minute True-Motion Speed Vectorand 3-Minute Collision Risk Area), the vectors cross in the final 3 minutes, highlighting the risk zone or area.

The last 3 minutes of any speed vector defines your collision area(equivalent to the turning distance needed at current speed). In Figure 3-2, the vessels' vectors show they will pass the same collision position at the same time, confirming an imminent collision. While the exact time-to-collision isn't always visible on ARPA or AIS displays, check TCPA values to quantify it.

The Lesson in Intuition: If the OOW had practiced reading "Crossed Points," he would have "felt" the overlapping danger. He would have seen that as soon as he cleared the fishing boat at 1948, he would have only 120 seconds before the next "X" with the CF Crystal. Reading the vectors transforms abstract CPA numbers into an immediate sense of physical danger.

The "Vector Halfway" Rule of Thumb

You can estimate your survival time visually without a calculator. Look at where the Crossed Points is on your own speed vector:

• The Halfway Mark: If the "X" is exactly in the middle of your 6-minute vector, your TTCis 3 minutes.

• The Physical Reality: If your TTCis 3 minutes, you are at the edge of your "Space Ship." As we have emphasized, 3 minutes is the limit of physical control. If the "X" is at the halfway point of a 6-minute vector, you must act immediately.

  Captain’s Habit:

  A steady bearing tells you there is a risk. The Crossed Point tells you where and when it will happen. By habitually extending your vector lengths (from 6 to 9 or 12 minutes) on the radar, you "probe" the darkness to find these hidden intersection points before they enter your 3-minute "Space Ship" zone. This is the essence of Rule 8: taking action in ample time.
  
  Captain’s Tip:

  If your radar doesn't show you the future automatically, you must command it to do so. Speed vectors are your "Collision Stick." Use them to touch the threat and push it away before it reaches your 3-minute Space Ship. We don't wait for uncertainty to arrive; we resolve it 15 minutes in advance.
  
  

  The "mystery" of the CF CRYSTAL collision is solved through early, decisive action. By 1939 hours, a competent OOW should have initiated the following plan to mitigate human error and the distraction caused by the fishing vessel:

• Alter Course to Starboard: In accordance with COLREGS Rule 15 (Crossing Situation), ownship (Sanchi) must give way. A positive 30-degree turn to starboard (shifting heading from 358° toward 026° or more) is required. This must be done in "ample time"—at approximately 4 nm DTC. With 11 minutes remaining until the projected 1950 impact, this allows for the vessel's 3-minute turning lag.