Hull side Dive door

I have been trying to figure out how a hull side dive door works? I am talking about a flip down door with steps incorporated. Identical to the ones on "Intrepid" boats.

How do you raise the door effortlessly? what kind of mechanism is involved?

 

Could try gas struts like the ones on minivan tailgates. Or pulleys and cables, with counterweights inside the hull, like a bascule or lift bridge.

 

Still trying to figure it out. gas or hydraulic struts, pulleys ... things could be easy easy if the door would flip down to an angle of 90 degrees but the door should flip down to 180 degrees and reach underwater, obviously the door handling should be from the deck of the boat as easy and no backbreaking as possible.

Suggestions will be greatly appreciated.

 

Maybe a clockspring type arrangement at the fulrum, a bit like a mouse trap, simple, low cost, should work ok.

Splint