The ocean itself is often associated with femininity. The Mesopotamian myth Gilgamesh relates that the ocean came from the goddess Tiamat, and in Greek mythology, the goddess Aphrodite (or Venus in Roman mythology) emerged from the sea.
So why are women who "transgress" (intentionally or not) cast out in the ocean? In the case of Custance (who transgressed by marrying a converted Christian) and Danae (who was the instrument of her father's doom), they are isolated and dependent on outside forces to keep them safe. However, Albina and her sisters keep themselves alive with no apparent divine help. They must be utilizing the ocean. And yet, Custance and Danae are depicted as pure and righteous because they depend on a force independent of the ocean. Could the ocean be seen as a dangerous thing for women to engage with? An unknown feminine force?
It's peculiar that capable, strong female behavior is attributed to evil Satan-doinking murderesses, while 'moral' female behavior depends on the protection of the Lord. The sea and these two tales about it may represent medieval anxieties about womanhood and female power. It seems that according to the Man of Law's Tale, the only acceptable form of womanhood would be to be passive and frightened and waiting when wandering the ocean, while mastering it or exploring it represents a danger to the role of females in Medieval English society.