All these answers are about right. If you want to get a feel for what it is like, get 3 or 4 buddies together and in your closet, set up an exercise bike, some free weights and a couple mats. As well, buy the oldest boom box you can find. Get all 3-4 of you in the closet, shut the door and play the boom bax as loud as it goes and strt your work out. As an added bonus, see if you can get a buddy with a machine to rock your house back and forth at the same time!!
Actually, as was said, the ships are far better than 10-15 years ago (On my last steamer GATINEAU in 1998, we had two stationary bikes-that's it) and I know from my experience on the CSC Project, designated gyms are being accounted for in the future RCN fleet. About the only challenge is getting time on some of the stationary equipment (though there are sign up sheets). If you are lucky enough to deploy without a HelAirDet, you have the hangar(s) too and usually extra gear is brought in. Bare in mind, that the Flight Deck is still green (operational) and if a nearby AC is in distress, you WILL be made to vacate the hangar 'at the rush'.