To be honest I've never had any issue been on many submarines (not served on them) including an Oberon class so I can relate but having worked on some ships in the past it was easy for me to do and go anywhere i had no fear i even used to fall asleep in the steering gear room !
I was lucky enough to go to sea on two submarines and dive down HMS Turbulent and Torbay thinking back that was a long time ago !
Inside the Foxtrot by
Blair shaw, on Flickr
I didnt find anything at the other end the door was closed! what you dont realise is these tubes are acctually quite long and im not exactly small and even my 140kg friend still had ample room to spare