Here is my $0.02 worth for boarding ladders. 

Mine is a 3-part folding ladder that attaches to the jib tracks on top of the bulwarks.  It is made of 1" ss, the slides that lock it and carry the legs are 1 1/4" ss and the hinge links are 2".  The ladder is extremely well made; there is no name on it and since it came with the boat I have no idea what it cost or where it came from.  I've put a lot of pictures up if anybody wants to duplicate it.

The bottom 2 rungs are in the water making boarding very easy and it folds up against the life lines ready to deploy at the tug of the tie line.  I can deploy it from in the water, just have to watch it as it comes down.

Brian Lumley, Valcor/T37/#555