A book with an ocean wave doesn't ring any bells. One edition of AWDwR has a hammock and an ocean, but I don't think that's what you mean. The Well Grounded Rubyist is okay but yeah, you'd definitely need good OO experience first because it doesn't go into OO basics whatsoever. It does cover the dynamic features of Ruby quite well though. I also forgot to mention the Sitepoint book - Build Your Own Ruby on Rails Web Applications. An excellent hobbyist book. I suspect pro developers might find some issues with it though (without cracking it open again I can't elaborate on this but I did hear some comments, despite liking it myself).
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