Simple Solution for that Problem.
Grab a Mantawith a hook - hook the Walrus up
Transport the walrus into deep Water some 100m away from his stern and drop him into the water.
Dock the manta and move your carrier very slow to the walrus that the walrus passes your carrier hull slowly within guess 10 m distance to his docking port.
usinge the 3rd person view helps alot !
Change to the walrus and press f as soon the dockingsysmbol shows up
Walrus will be docked even without fuel.