We have cruised twice in March and found the temps to be a little cool but swimmable. In March 2002 a cool front had just moved through and the daytime temps were about 80 and the water temp was right at 80. As long as the air temp was warm it was fine for DH and I. However, on early excursions or cloudy days in the upper 70's it was chilly. It only kept us out of the water once in Cozumel at a 9AM beach excursion...the air just wasn't warm enough. Also, some of the days on the sun decks were chilly as they were overcast and it is quite windy. We ended up wrapping our towels around us rather than under us to stay warm.