A requirement for a 2 mile CPA is common in the open ocean. Someone on this forum pointed out to me that CPA/TCPA limit (time of CPA) is better then a CPA only. This is correct. I think of this as boxing in the watch officer to limit how much risk can be taken without authorization or assistance.

One issue that can arise; in coastal waters and in heavy traffic the watch officer can avoid close CPAs by taking the ship into unsafe waters. The watch officer is not safely “boxed-in”. With paper charts the defense was to draw “no-go” areas on the chart.

The ECDIS has a better tool, the cross-track error settings. A requirement can be added to the standing/night orders that the master must be called if the watch officer plans to cross outside the ECDIS cross-track error lines. Some care is required in selecting the XTE distances for each leg.

These requirements to call the master: CPA / TCPA / XTE all tighten up watch officers decision box.

At anchor we used to write in the night orders something like “take frequent bearings and ranges” and “call if the anchor drags, if winds increase or if in doubt”

Now we use the ECDIS to draw circle around the ship’s anchor position. Still write the part about frequent bearing and ranges but also: “call if ships position falls outside anchor circle.” The circle is the box.

In general, more vague language such as call if visibilty is reduced or if winds increase is replaced by more precise language: “call if visibilty is reduced to 3 miles or less” and “call if winds increase to 35 kts or more” and so forth.