While people always associate the term 'disembarkation' to mean leaving the ship at the end of a cruise, it's actually the correct term to mean leaving the ship at any time. For example, to use the term disembark at a port means the same thing as going ashore and is technically using the term correctly. So if someone were to say, "I'm disembarking for the day in Cozumel," they would be using the right term, but it would probably create confusion among some people.
Debarkation is also a term people use to mean leaving the ship, but in the formal sense it means to unload from a ship. And while it's used to mean 'people' are unloading from a ship, it's more accurately associated with freight since the terms 'loading' or 'unloading' are not normally applied to people walking on and off a ship.
Can be confusing for the first-time cruiser, but most people use the terms interchangeably to mean the same thing and usually to mean leaving the ship at the end of a cruise.
But now here's a question; if we refer to passengers getting on the ship as 'boarding', what is the opposite of that? The antonym of boarding is to evict or eject, so should we say when it's time to get off the ship that passengers are being evicted or ejected??