Many answers...
Happy New Year, Darline!Boats don't move in much of the Bahamas at night, except in the deep water passages and across the Banks. No nav aids, variable current, etc. But more broadly, what you imagine - two folks switching off - is the basic answer. How this is done, and how conscientiously, varies quite a bit from boat to boat. We recently returned from 2 years in the Caribbean, including a lot of multi-day passages. Like many before us, we used an egg timer in the cockpit to help us time our 720-degree visual sweeps, punch the radar button and scan it, post an hourly updated DR (actually, a fix given GPS these days) on the paper chart (just in case the laptop crashed...), check the batteries, check how things on deck look, etc. Inbetween egg timer Brrinnngs! we sometimes doze. What to set the timer for is determined in our case, as with many others I'm sure, by running a worst-case determination of a ship approaching us after our last sweep. Let's say a 25 kt. cruise ship or tanker is coming over the horizon off our bow and our combined closing speed is 32 kts - how long before it's at 2000 yards, allowing us time to maneuver away after spotting it on the next sweep. We usually sweep every 10 mins or less. (Illogical tho' it might sound, it's harder to do this conscientiously, relentlessly during a bright sunny day in good weather than at night when you're dead tired. Daydreaming, book reading, munching in the galley all make us forget to set the damn timer!) A radar with a 'guard zone' feature can be a big help to short-handed crews, and has been a huge help to singlehanders these days.Once offshore, you will quickly become aware of how much a priority it becomes to rest at every opportunity. Basically, we stand watch & navigate, occasionally eat (sometimes not much), cat nap, take an afternoon snooze, and sleep some of each night. This is almost mandated by circumstance if you're offshore many days; it's usually very tiring work.Jack