Regarding rope ladders.

I have never tried climbing a rope ladder while in the water, but on land you always have to climb them sideways. Ie. not climb it on the front side like you do with a regular ladder, but 90 degrees to the side. Perhaps this would work in the water as well?

There are 'rope ladders' with aluminium steps, that would sink and not float a bit like regular rope. In technical rock climbing 'rope ladders' are quite common, perhaps something usable could be found cheaply at a climbing store if someone wants to try it out.