"a train passes another going in the same direction " - true, in the same way a car passes a slow-moving vehicle on the road.

"but meets one that is coming in the opposite direction." Yes, they meet…and they PASS, going in opposite directions.

A ship's captain is not going to have a copy of Fowler's Niceties on the shelf alongside his sailor's almanac.

Spell it out in the rule, something like:
Two ships travelling in opposite directions are not permitted to pass each other in (a certain stretch of water). The northbound ship has the right of way.

The saying is, 'like two ships passing in the night'. To say, 'like two ships meeting in the night' has a totally different meaning!