In the avoidance of collisions keeping watch plays a central role. Here are some suggestions as how it can best be arranged.
Although when coast hopping it's possible to arrange who and when those on board stand watch, this becomes impracticable for longer trips – say more than a couple of nights. And here I'm assuming that in this modern age that some form of mechanical self-steering is available, whether wind or electrically powered, and that the watch-keeper can therefore attend to keeping a lookout and perhaps a spot of sail trimming.
Of course the precise arrangement depends upon how many are aboard and the nature of your surroundings. Crossing a busy channel such as the one that separates England from France can keep you a lot busier and be more stressful than crossing an ocean. In 2015, Chele and I sailed from the Canaries to the Caribbean in company with Anne – a long-standing friend and very experienced sailor. We agreed that each of us would stand a three hour night watch: 2100 to midnight for Chele; midnight to 0300 for Anne; 0300 to 0600 for me. The original idea was to rotate them but the ladies opted for regularity so who was I to disagree? During the day there was no need for watches since the tropic heat made life beneath the cockpit awning more agreeable than the oven that Shindig's cabin became.
Also, the traffic was extremely sparse. Including contacts courtesy of AIS (Automatic Identification System) we didn't encounter more than a handful of other vessels until we neared Barbados. And even then it wasn't exactly crowded.
With a four person crew your options widen. The arrangement below shows a popular approach. The crew splits into two pairs – A and B making the first pair and C and D the second. The pairs themselves then divide, each spending 90 minutes on deck keeping watch and 90 minutes 'standing by ready for action if needed'. Every three hours the pairs change. In our example C and D take over while A and B go below to rest. With luck it's possible that all participants could spend only 6 hours per day on deck. In dodgy conditions some would consider that a blessing!