The sink hole rumor sounds bogus, but best I can tell is that the newer boats are the biggest (not only) problem, Back row in particular, if the boats stack up (like at unload), it seems way too easy for the boat behind it to hit and jump up (and over) the back of the boat in front of it. Weight configuration and use of the back row would be affected by it, but that's probably where the safety concern comes from. If someone were in the back and the boat behind popped up, it could hit them.