A Question about “Raiders of the Lost Ark”

Okay, towards the end of the movie, Indy has the ark on a boat. A German sub stops the ship. They take the ark and Marion onboard the submarine. Then we see Indy swim over to the sub… dissolve to a map sequence.

I’ve never really considered it before, but are we supposed to believe that Indy stows away aboard the u-boat? Because that seems ridiculously unlikely. First of all, don’t you enter a sub through the bridge? And even if you get on it, where is there to hide? How can you possible stay unnoticed for days?