Ferry Croatia-Italy

I would like to know the difference between 'couchette' and 'cabin' on the ferry from Dubrovnik to Bari?

Also, what is the 'deck pass' really like for an overnight trip? Are there seats or just a big floor? In late April will it be cold / wet / crowded / rough seas? Are the 'last minute beds' purchased on board cheaper than prepaid?

Thank you!

varies per ship. and why ask this here: most boatcomps have some website nowadays.
Couchette is the all-TRAIN word for a ''bunk,, this shared hostel style rooms, WC/bath out in the gang.
cabin is just that: but for just 1 it will cost the earth.
Deck in ANY ship: any place you find, in or outside. for the more lyuks looing recline seats the word is PULLMAN and you should have resevred+paid for them (on most ships noone cares and anyone runs for those left empty)
the fare is the fare, varies with peak/season and NO further discount [ecxept if you are IT military or have acard stating you have some very big family or so. will ONLY apply to EU/Hrvatska anyway

thanks.