So we have a new third mate, making his first trip at sea. Sharp guy, learns fast.
The ship is transiting through a short passage between reefs, maybe about four of five miles wide, daytime, good visibility. At the end of the passage there’s a turn into more open water. The ends on both sides of the passage can be easily seen visually and are marked by aids. There are a few fishing boats moving around in the vicinity.
A simple problem by eye but that’s not how the third mate does it. Instead he monitors the distance to the turn using the ECDIS and the fishing boats using ARPA. Which means instead of keeping a lookout he needs to race back and forth between the two display with an occasional glance outside.
This is just an example, almost all third mates do this and more than a few officers of higher rank and a lot more experience.
This, I think is easier said than done:
Push officers to realize that the change in a rough visual ‘bearing’, taken from a fixed point within the wheelhouse, is sometimes good enough to determine if any risk of collision is likely to exist. This beats running to the radar every few minutes and playing computer games there for each target. It also helps in keeping a good lookout.
From here. Losing the Plot