"Eat" as past participle, however, was archaic or rude even in Coleridge's time.
76--*vespers*.

Properly a liturgical term, meaning the daily evening service in church; then in a more general way "evening." The Century Dict.

gives no examples of its use as a nautical term.

Probably Coleridge used it to give a suggestion of ante-Reformation times.

The more familiar word for the evening service in the English Church is "even-song," but Coleridge in line 595 prefers "the little vesper bell" for its suggestion of medievalism.
6, 97--*like God's own head*.