A ladder for a dive-boat should be long, so that it goes well below the surface - you should be able to step right onto it without pulling yourself up - should slope outwards, not hang straight down, should have flat rungs with a stopper at the end (so that you don't slip off) and should extend well above the dive-platform and have proper handles at the top. Unfortunately, few dive-boats have a good ladder. Note that this is a safety issue as much as a convenience issue. These drawings, borrowed from http://www.cisatlantic.com/trimix/ , show examples of two types of good ladders - an economy version and a de luxe version.