Oh boy we had a similar experience. When we left the South island port the Captain said all is well but the swell is "moderate". Everybody cheered when we hit the first few waves and the water splashed up the sides of the ship. That quickly turned sour...green people all over the ship Man they stank that ship up in no timei was talking about my return ferry trip from south island to north just today.
even the bar staff were being sick it was so rough... i had to pour my own pints as i was the only one left standing (i did leave the $s).
One guy was lying with his head on the table, in a puddle of vomit. The vomit gently to and froving away and then back to him as the ship swayed from side to side