For the posters looking for info on Cocos I can help a little...
We dived from the Okeanos, altho a little tired (I hear it went to drydock in Ecuador for a refurb following our trip in April 2001) was still a fine boat. Long crossing, 37 hours from Punta Arenas. Seas were calm, tho.
Crew was excellent, food was plentiful and usually tasty. Two zodiac pangas and a 21' fiberglas hull chase boat to dive from.
Diving was big animal action 24/7....hammerheads, white-tips, silkies, silver tips, marbled rays, mantas. There was every type of dive condition...great vis, lousy vis, calm, rip currents, big surge. You name it, we saw it. Our first (checkout) dive was in a fairly protected area and we still had to claw our way along the bottom, holding onto rocks to keep from being blown away.
This is not a place for the timid or easily spooked diver. Down currents were very strong at Alcyone (best place to see hammers). We would position ourselves in the rocks at 120-135' and let the hammerheads come in over the top of us for some VERY up close and personal viewing. (within 5').
There were few dives that were not high adrenaline affairs. Mating white-tips and baitballs provided some great photos.