ἐκ δ᾽ εὐνὰς ἔβαλον, κατὰ δὲ πρυμνήσι᾽ ἔδησαν:
ἐκ δὲ καὶ αὐτοὶ βαῖνον ἐπὶ ῥηγμῖνι θαλάσσης
and etc, here imperfects and aorists are used without apparent difference in meaning, Further, βῆ, τίθει etc.
When I read this, I just imagine that the anchoring stones were already cast and the ship was tied to the shore using the dedicated ropes (by some of the soldiers), therefore the aorists, and when the ship was thus secured, all the others ‘began the process’ of getting off the ship and moving to the shore, hence the imperfect.