This is a thought experiment that my friends and I (physics graduate students all) were pondering while we should have been doing Jackson homework. Consider a boat traveling at relativistic speeds. From the boat's frame, the water is contracted, and therefore is more dense. This would increase the buoyancy of the water and keep the boat afloat. However, from the water's frame, the boat is contracted, making it smaller and denser. Since a smaller amount of water is displaced, there is a smaller buoyant force, and so the boat sinks. So what actually happens?