i only spawned one thinking it was just a simple vehicle model with thrusters attached
no idea why it crashed the server that first time a few hours ago
the reason people are getting the yachts is because of the Dupes page in the Q menu
it's a big catalog of random, interactive stuff made by the community.
you can spawn them at will with the Duplicator.
the only thing to do about this is to simply tell people to only spawn small or non-complex stuff from there, if they use it.
or just tell everybody not to use it at all