It varies by time of year--but monthly in a given direction is probably a rough estimate. Go to Cunard. Mostly Queen Mary 2 although I think they have a new ship that does some transatlantic as well. For crossings, my understanding is their ships with stabilizers etc. are better able to handle the North Atlantic than the average cruise ship.

Dates lined up for me on a trip late last spring and I enjoyed it. Would consider doing again.