The difficulty I have with this--and I'm going to defer to all the esteemed legal experts around the table--is that if someone comes onto my property and is injured in so doing, whether he's invited or not to come onto my property, I'm still liable for any injuries to him. What this particular clause suggests is that if you're going to make an exception for someone who comes aboard a vessel, which is the private property of person X, then you need to have consistency with the legal principles applied to someone who has private property that's not floating.
I'm not sure this would stand up anywhere. Why present it?