Yeah, that's what I thought it might have been as well. I guess I just assumed it was fine, considering that it let me place the shipyard there in the first place.
I reckon I would have uninstalled if it had been a larger ship.
And of course, all the beaches on every island are already covered in shipyards/foundations so it is going to take ages to find somewhere new to build one.
Oh well, keep trying I guess.