Not Sam, but I’ll answer anyway. Something floats if it weighs less than the amount of water it displaces. So if you have something that weighs 7kg, but has a volume of 8liters it will move 8liters(about 8kg) of water out the way, it will float. A ferry is huge, and mostly hollow. So while it’s very heavy (hundreds of tonnes) the weight of the water it displaces is much greater and so it floats.
Hey Mishab, Ezzy explained it nicely.
Thats also why ships sink occasionally – if enough water gets inside the hull, and enough air (much lighter than water) is replaced by water (not lighter than water, obviously), the weight of the ferry becomes larger than that of the displaced water and no longer floats.