Do two ships close alongside each other in a choppy sea tend to be attracted together?
I have read conflicting reports of this phenomenon. One of them, saying that they do, gave a thorough but highly ... synoptic I think might be the right word ... or top down maybe ... explanation in terms of the re-radiation of the wave energy by the pair, & the state of the waves between them, & how a sort of pressure is a property of a plenum of waves that would be expected to be greater beyond the ships than between them, rather than "volume δV of water acts with force δF on area δA of the hull", or suchkind of more bottom up argument. I can't reproduce the argument in detail I'm afraid, but it was thorough, with each ship bobbing up & down represented as a monopole and the two ships creating an energy-field mediated by the waves, and arguing that the energy-field would have such-&-such a shape & that kind of thing. But I would have thought that a definitive answer to this question would be easier to come by than it seems to be, what with the maritime art being such an ancient & noble & widely practised one. If anyone's curious about this I'll see what I can find about it, as I'm recalling from memory something I read in a fluid mechanics textbook years ago. But I have seen mentions of the existence of the phenomenon in a fair few places.
Got a bit more detail already: some say it's an analogue of the Casimir effect.