To me this song isn't some cryptic message of life, it's just a seaman's tale. There are lots of stories about sailing ships, some pretty fantastic, but all seem to have a general kind of haunting thread about them at least to me.
One of my favorite poems is The Rhyme Of The Ancient Mariner. Multi-page poem that runs along in the same genre as this song. Procal Harum is one of my favorite bands that had enough courage to publish songs like this back in the days when every other band was singing about lsd trips.