Re: Forces on a dockline while docking....
People ferries and water taxis use a similar technique when they make their quick unload/reload stops.. Usually in fwd gear and the rudder turned away from the dock.. Thay basically motor against the spring line holding themselves on the dock.
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
1984 Fast/Nicholson 345 "FastForward"