A Cancun catamaran, the Sea Star, sank with 126 passengers aboard leaving one young woman from Texas hospitalized in a vegetative state. Initial reports claim the vessel was overloaded but owners say the cat could carry 250 passengers. You can find a photo of the vessel here.
I can't comment on whether the vessel can carry 80, as some people are saying, or 250, as the owners say, not without more info. What I can say is that certificates are written specifically with designations for capacities on upper and lower decks. Could be the upper deck had a capacity of 80 and that there were 126 people up there at the time of the accident.
I mentioned once in another post of a ferry ride I took from Cancun to Isla de Mujeres. The ferry was a large wooden held together with coast of paint. If I had been a Mexican Transportation Safety Inspector I would have condemned the thing on the spot.
Pictures of the Sea Star suggest it was a more modern vessel and in much better condition than the ferry I was on.