Good luck with your new boat! I bought a used car that smelled of cigarettes. My mechanic suggested that I use fabreeze on the fabric and put fabic softener dryer sheets under the seats. The smell was gone in three days. Can't say it will work on a boat but it sure worked on my car!
This works surprisingly well. Febreeze and anything that absorbs. Charcoal, baking soda, dryer sheets, etc. Ask the owners if you can spray down the boat and drop off a few dryer sheets, then come back in a week and check the smell again?