I am afraid this is definitely a new bug. My mesh boats are rideable vehicles, so no attachments ! At some crossings the boat just vanishes and it are always the same sims where this happens. Besides that, it started to happen after a major update some weeks ago. Clicking the boat will resolve it but clicking a vehicle is not very handy when sailing or flying, sailors and pilots know what I mean.
Edit : Just talked to some sailors. it is not a bug, it are your graphics so I was told. Clicking the vehicle will help but then the vehicle stops. First press control/alt and then click the vehicle, it will rezz again without a stop.