We just returned from a Panama Canal transit on the Coral Princess. One very often asked question is about laundries on board ships.
The Coral Princess has a laundry on every passenger deck. Both the washer and the dryer (4 of each on our deck 5) cost $1 and you needed 4 U.S. quarters. In the laundry room was a change machine and a machine for purchasing detergent and softener, also $1 each in quarters. There were also two irons and two ironing boards in the room.
I only used the washers. They held a lot of clothes and the clothes were spun so dry at the end of the 40 minute cycle, that I simply brought them back to the cabin and hung them on hangers and my clothesline to finish drying.
I used the machines twice, once on a port day when we stayed on board and a second time on a sea day and I had the rooms to myself. I would have no problem planning on using them if we sail on the Coral Princess again.