There are absolutely Ghost ships out there since boats are, for various reasons, abandonned by their crew every year. Most either sink, run aground or are salvaged when they come close to shore since ghost ships are a danger to commercial traffic. However, there are no centuries old ships out there. Wooden vessels simply don't survive for that long, even if they miraculously avoided reefs, shallows and shores for that long they would have been claimed by rot long before they could become that old. The same is true for steel ships which will eventually rust, salt and water are an unforgiving combination in the long run. So what is the oldest one we've discovered? The SS Baychimo.

The SS Baychimo was originally commissioned as SS Ångermanelfven by the Baltische Reederei GmbH (Baltic Shipping Line), built in Lindholmens Mekaniska Verkstad in Gothenburg, Sweden. She originally saild out of Hamburg to various ports in Sweden. At the end of the Great War she was given to the UK as part of the war reparations paid by Germany and acquired in 1921 by the Hudson Bay Company for use between the company fur posts in northern Canada and the Scottish port of Ardrossan. In 1931 the ship got stuck in the ice near Pole Island and was abandonned by about half of her crew. The other half set up a temporary shelter some distance away from the ship, intending to wait out the ice and resume sailing. After a severe blizzard the crew returned to check on the ship only to find her gone. It was assumed that the storm had driven her out to sea and the ship was abandonned.

The Baychimo did not sink however. In fact she proved remarkably resilient and remained afloat for at least 38 more years in the waters of the Beaufort Sea. She had been borded numerous times since by commerical captains, explorers and local populations but the ice and weather always prevented an organized salvage attempt. She has not been seen since 1969 and is presumed sunk.

In theory, if you had access to all the data at every P&I club or every Hull and Machinery insurer in the world, you could conceivably construct a list of ghost ships. Barring that, the question is not truly answerable, but it is somewhat quantifiable.

As to the scale of the question As of today, Lloyd's List Intelligence (sorry, expensive proprietary data - but I include other sources below) says there are 191,418 ships in the world, include those "dead" and under build. That number doesn't include many smaller workboats, small (self-propelled) barges, or naval or other sovereign vessels, etc. 48,795 of those are listed as "dead." Dead in this context usually means sent to the breakers or in some cases already broken up. But any ghost ship would be among that 48,795.

Fortunately there are public sources to help narrow this down. At the free site Equasis you can perform an - in some ways - more granular search than at Lloyd's. There is one ship under the category of "continued existence in doubt." The other two possible categories into which a ghost ship might fall are the two categories where the whereabouts of the ship are not necessarily known. These are, "In casualty or repairing" - 476 ships, or "To be broken up" - 158 ships. The reason I selected those is that all of the other categories necessarily imply a ship is trading or at a particular place. So the likely potential pool of ghost ships is around probably more than 100 and less than 1,000..

Two other factors make the question problematic to answer. The first is that vessels sometimes turn off their AIS (a kind of location beacon) for extended periods of time for good reasons - extended repairs, lay up - or nefarious ones - sanctions breaking, avoiding arrest. So even if you could search every single ship in the world by name or IMO, you would get a lot of ships that do not have a current or recent last location because they are dry-docked somewhere or paying a visit to North Korea.

Finally, in the trade press, the term "ghost ship" has a particular meaning at odds with the common conception of a ship abandoned and adrift at some unknown location. In the trade press a ghost ship is one that has been abandoned and its ownership is unclear; very occasionally it will refer to something else, e.g., a ship being supposedly being built but that may not be completed (or other highly specific reasons). Which is a long winded way of saying there's no way to reliable search the trade press for incidents of ghost ships as popularly understood.