This is a common misconception

Containers do not float below the surface. An object floats or it sinks. There may be an hour or two where a sinking container rides near the surface, but is of statistically little significance (I would not call a sailor claiming such to be a liar, and I have called people out who did so, it's theoretically a possibility for a very short period of time, but if it happened to me my next stop would be the lottery office). I recognize that the vast majority of objects on the ocean are floating very low on the surface are extremely difficult to see, and with the majority of their surface below the waterline, will invariably hole the boat below the surface, but being that this chapter is about objects sinking, I think it best not to get too loose with the rules of physics. Further, when shipping containers are loaded, they are not carefully loaded to maintain fore and aft c of g, and thus will usually ride with one or more corners and edges below the waterline. With only one corner floating above the waterline, it can be well camouflaged to the unsuspecting eye, especially considering various lighting conditions we sail in. But they don't float below the surface. People on the west coast often claim logs float below the surface, but they don't: a part of them always floats above the surface. You must keep am eye or for the small signs.