I want to add one more thought on the idealized version.

You have mentioned gravity(which would attract on a large scale) and surface tension (which would cause the matches to attract). But imagine that the ships spot each other at one instance and did not at some earlier time. Well this implies that the ships ARE moving towards each other and thus ignoring friction they will drift closer, but how much closer of course depend on their relative courses.

Another thing that actually do pull ships together is the currents around the ships. As the ships plow away water this water flows back at its stern. This will cause two ships going fast on a parallel course close together to crash. This is a common danger for fast missile boats and alike.

Well again wind and ship movement were not factors. Both ships were completely becalmed and adrift.

As for why they did not spot each other earlier that would mainly have to do with weather conditions affecting visibility range.

Because a ship displaces its own mass in water, wouldn't a certain volume of water containing a ship have the same mass as the same volume without a ship?
If so, wouldn't that make the attracting masses on both sides of the ship equal?