The boat ladder isn't fixed; they pick it up and set it over the side (kind of like an upside down U) to let people climb back aboard. Seas during my trip were about the most consistently smooth I've seen. I used the dangling 'ski rope' over the side to hold on (not a big deal, but at times there's some surface current) and move toward the back of the boat; when it was my turn to reboard, it wasn't hard to move down and grab the ladder.
I pay attention to seas a bit, because my lower back isn't what it used to be (so the 'bouncing' when a boat's underway isn't pleasant) and my wife and a friend I used to dive with were both prone to sea sickness; I'm not (unless our kid wants to me ride the Tilt-A-Hurl,er,
Whirl) with her at a fair, but I think about it.
On an unrelated note, regarding weird souvenirs, I brought this back for her.
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Richard.