No, you don't need formal wear for the 3 night cruise. We did the 3 night cruise in 2001 and didn't see anyone in formal wear. Men wore jackets and ties to Tritons, but that was as formal as I saw.
No formal wear needed at all on the 3 or 4 day. As Zandy suggested a jacket/tie combo would be nice for Triton's or Palo. Resort casual everywhere else (no shorts or jeans).
We just came off the three night. Hubby took a suit, because we ate at palo. He definately didn't need a suit in tritons. If you don't want to eat at Palo, I wouldn't even drag a suit with.
Button down shirt, tie, slacks and you're set. Skip the suit and jacket unless you really, really, really want to lug it along with you (and have it take up all of that suitcase space!)
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