Crossing the Bar

"And may there be no moaning of the bar
When I put out to sea,"

Well, it wouldn't be my blog if I didn't talk about how I did not understand at least one poem. :) And here it is! What exactly is the bar that the speaker is talking about? I feel as if it could shift in meaning from the first stanza to the last because of how it is used in context. In the first stanza, the speaker is talking about going out to sea, so I first took the bar to mean either the oar (I pictured them on a row boat) or a sand bar. But a sand bar doesn't moan so that did not make sense. In the last stanza the speaker says, "I hope to see my Pilot face to face/ When I have crossed the bar." I took this bar to mean that he/she left life, as in died. The Pilot to me seems to symbolize God because he guides us in everything that we do.

Maybe I did know more than I thought I did...