Good luck with your adventure, however in answer to your query, no,
cruise ships do not have volunteer positions. Just
google cruise ship jobs, or look under
employment at Princess Cruises' website (or others) for job opportunities.
But I will tell you most, if not all require a six month
contract and all cruise ships jobs are considered
commercial ship's crew. You get paid weekly (in cash, tax free), get free room and board, but
work seven days a week (with a fair amount of down time though).
If you're not a drinker you'll become one or expect to spend a lot of time alone (the tradition of the seas die hard). They will not take anyone looking to use their job as
passage to somewhere. You could get to Hawaii and formally quit and they'll let you off there, but they take the
price of a plane ticket out of your pay, whether you use it or not, since they can't just dump you someplace.
Also, when you sign up there's no guaranteeing you'd be on a Westcoast to Hawaii cruise (which are rare).
I have a friend who's been working on cruise ships for over 15 years now (swore she would do only one contract) but good way to save
money, see the world and you can take six months of whenever you choose and come back to it. Hope that helps. Cheers