I still have yet to see an argument made that speaks to the fact that regardless of what you may desire at the moment (immediate parking for your pleasure boat), you are out there sailing by choice - and your desire
to dock isn't an emergency or necessarily a situation that should give you easement rights over another private property.
While the dock may be public, the vessel you are commandeering and boarding in order to access that dock is not. It just strikes me as a very entitled attitude to have, again in light of the fact that you make the choice to potentially sail up to a dock that may not have the room to accommodate you.
I don't see a justification (unless in an emergency) as to why you are entitled to park your boat at the risk and expense of another boater who got there first.