I think you'd be pretty ok washing them on ship. I've never taken a cruise before so I can't speak from experience but I don't know of anything that could 'happen' to them that couldn't be fixed when you got home if really necessary. The only thing I'd be concerned about is other people's reactions to your laundering dirty diapers in a public facility (personally I think it's just fine but you never know how others will react) and possibly then having to purchase disposables on board where you'll surely pay a LOT more than you would if you bought them before you left.

You could always use a combination, maybe rinsing the diapers really well before putting them in the pail/bag and just waiting till you got home. 7 days is quite a long time but you could maybe just do one small wash say on day 2 or 3 and then wait for the rest. Or just use disposables for the first 3-4 days and cloth after that and just wash when you get home.

You could always call the cruise line and see what they say about washing on board ship (you can always use the 'my baby has an allergy' excuse if they they give you problems). If you do wash in the public facility (I too would never have the guts to have them washed by someone else, not to mention that they would probably use bleach, which is probably the one thing you can't 'repair' when you get home) I would make sure to do only small loads and make sure the poopy ones were well rinsed first. That will make them easier to wash just in case the machine aren't the greatest, plus it'll minimize the smell in your cabin and lessen the chance that anyone will react (or even know) to the diapers. I'd do a small load every night... Plus it'll cut down on how many diapers you have to bring in your luggage.

Oh, and if you do need to use disposables and are afraid they'll leak or especially 'blow-out', put a diaper cover over top to help contain poop and help prevent wicking.

Karen.

Oh, and there's always the possibility of washing some or all, by hand in your room and then just drying them in the ship's dryers. Sounds gross I know and it's not my first choice but it works and at least you wouldn't have to worry about breaking any 'rules' or grossing people out.

I just went on a camping trip for a couple of days and I don't know what in the world I was thinking but I didn't pack anywhere near enough diapers (I think what happened was when I first started packing some of my diapers were drying and I was going to get them later and then forgot). I just took a few dirty ones to the camp washroom (they had sinks outside the washroom so I used those), rinsed them in cold water first then washed with hot water and some of their hand soap (really not ideal but I figured for one wash it wasn't the end of the world) and then rinsed in hot water. 

Maybe I'm just getting really used to handling poop and pee after 4 kids but I really didn't think it was that big a deal. I guess maybe after changing diapers for 10 years straight (no kidding!! closest to a 'break' I got was for about 1.5 years it was 'only' a nighttime diaper) nothing fazes me anymore... I wouldn't want to do it all the time but to avoid having to run to a store to buy overpriced disposables, it was totally worth it.

Karen.