I took a boat, about a 70 foot steel hull, from Colon City to Cartegena back in '06. It was called "Junior", and at the time it was doing about ten round trips a year. Officially, a coconut boat. Matteos was the Captain. Negotiate a price beforehand. Use caution, there are other very dangerous captains and boats... some we were warned might take our cash, ride out five or so hours to sea, throw us over and come back to sell our pretty gringo bikes. Boat I(we, five motorcyclists met on the internet and ended up on boat together) were at sea six days making sometimes odd stops at the san blas and colombian islands. Not carnival cruise islands, and there was always an air of some criminality nearby. personally, i dont think i would do this again, opting for a flight from panama city, but if you're bent on a surface route as i was, there are ways. just ask around at docks and hotels when you get there.