I just looked on NCL's web site at their doc requirements and it doesn't say whether the passport can be expired or not. The safest thing would be to renew your passport, but if you don't want to do that, I would call the cruise line and ask them. Get them to send you whatever they tell you in writing.
Land Cruise, Britain and Belgium
Now posting as MichelleP.
I was on a Carnival Cruise Lines a couple of weeks ago, and after I embarked- I had to go to the office to ask this man a question regarding flight information-anyway...there was a couple in there arguing with a carnival rep that the guy had acceptable ID, and the woman had an expired passport. They wouldn't let her on. The guy was furious because apparently it was a family cruise and his whole family was already on there, and he didn't want to go on without his girlfriend. I never found out what happened, but I looked for them on the ship and I didn't see either of them. SO-Be safe and bring a Birth Certificate and anything else lying around.
I sailed on CCL last Dec. and the res. agent told me it was ok to use an expired passport as long as the exp.date wasn't over 10 yrs. old. I also brought along my birth certificate, just to be on the safe side.
Seems to me that getting an expired passport renewed is the way to go. We did ours by mail and it was quick and easy - got the form off the Immigration website. Better to be safe than sorry @ $7.50 per year since a new passport is good for 10 years.