Lots of cruise ships have one or more laundry rooms on board, and they can be a great convenience, but they have their risks.
I’ve gone to the laundry rooms on multiple cruise lines and one thing that has been consistent is that the fellow passengers can be ruthless.
If you leave your wet wash in the washing machine too long or your dry things in the dryer, they may guy tossed out to whatever is a convenient place to make room for somebody else’s clothes.
When I do laundry, it’s a pain, but I will stay in the laundry room the whole time to make sure my stuff doesn’t get tossed in the sink or walk away.
And if it’s something that can air dry I will just bring it back to my room and hang it in the shower.
Or if I have a balcony I will use towel clips and hang my clothes on the balcony to dry.
Typically there will be a machine with some options to purchase detergent, so unless you are particular about a certain brand of laundry detergent, there is no need to bring some on board with you.