A once-common word that has largely survived only as part of overwhelm, which was originally meant to overcome by whelming, but was later reinterpreted as an intensified form of whelm -- thus the coinage underwhelm, to fail at overcoming. Indeed, sometimes whelm itself gets backformed from overwhelm as having a sense of not being whelmed -- not so much underwhelmed but completely meh. The original sense was simply to cover over, as in to whelm something by putting, e.g., an inverted bowl over it. The word itself seems to be a 13th century coinage created by blending whelve, to bend over, and helm, to cover (as in what a helmet does).
The seventh wave whelmed the dingy and capsized us a hundred yards from shore.