I agree that your problem goes way beyond soiled underwear. Your DH needs some counselling along with his bypass, obesity problem. However, if you go ahead with the cruise, you can still buy absorbent underwear 'liners' in place of adult diapers that might solve the immediate problem. There are also very oversize pamper style adult diapers. If you choose either of these options please be sure to bring along a box of good quality garbage bags to tie each soiled one in before depositing them in the garbage cans. A miniature spray bottle (ie. Glade) for your room would also be advisable.
Inregards to the WASHBOARD, forget it. Take along a small bottle of concentrated laundry detergent and simply scrub items in the sink if necessary. (This should be HIS responsibility not YOURS). Perhaps he is not at the point in his recovery to be on a ship where there are sweet temptations "24/7".