There's a nice piece on "Crossing the Bar" at Wikipedia, not that it answers the original question.

I'm wondering if there are any sailors here who can give us more information on crossing the bar. The most significant bar crossing I know of, is at the mouth of the Columbia River at Astoria, on the border between Oregon and the State of Washington. At Astoria, the river goes straight out into the Pacific Ocean. Most other natural harbors I know of, have some sort of lagoon or bay separating the river from the ocean, or the river takes a turn at the end and enters the ocean at more of a right angle. But the Columbia River empties straight into the ocean. One can see an area of very rough water not far beyond the mouth of the river, and that area is a legendarily treacherous crossing - so local pilots are employed to take ships across the bar. There are shipwrecks on either side of the bar, one or two still visible above the surface of the water. I don't know what phenomenon makes the "bar" so treacherous, of how much shallower it is at the bar.

I'm wondering if the "one clear call" is a warning to crew and passengers about approaching the danger of the bar.

I also wonder how long "crossing the bar" has been a symbol for death - did Tennyson initiate it?

I'm also wondering about various musical settings of "Crossing the Bar." The only one I really know is the one by Rani Arbo. The copyright date I have for the Rani Arbo setting is 1997. Are there other well-known arrangements?

Although I once thought otherwise, I take it that Rani Arbo is a female; and that the members of her band, Daisy Mayhem, are all men. Is that correct?

-Joe-