When I was in Hanoi, I took a 3 days and 2 nights tour package to Ho Long Bay. This is a interesting trip if only you do not mind having long waiting time for almost everything. We had one night stay in the hotel in Cat Ba island and  another night sleeping in the boat (guess more co-ordination needs to be done). Most of the time we were on the sea. We had our meals on the boat, which included in the package. There was a free flow of beer on the last day.