In reply to mugglewump: I spent four months in exactly the same situation and will be spending another eight starting this May.
When I got back from sea I was climbing slightly harder than when I went away! This has continued to be the case.
The only loss I noticed was in my running ability. After a month or two of training ashore this was back to essentially the same level, if not better.
I had at my disposal a treadmill, punching bag, rowing machine, weight bench, dumbells, bar and more weights than I could possibly lift. I supplemented this with some therabands. There was a multigym style thing that allowed some other motions to be trained.
I did loads of core exercises, loads of upper body stuff and regularly ran five miles (all I could stand on the treadmill). I managed to use the climbing wall at Liverpool once a month, check if there is a convenient wall if you can get ashore for a few hours. Lots of dips, pushups, curls etc.
R