What action should I take against my captain for slandering me?

I am crew on a boat as a Guest Coordinator for a small non-profit organization. Last season, I struggled with the captain and his unfair treatment of me. Other crewmates also noticed how unjust the captain was being towards me, as did passengers. This captain is known for sleeping with young female crew members and some people suggested that since I was not sleeping with him, he was angry with me and therefore being cruel. He would make very rude, personal comments to me in front of passengers (such as calling me fat). Just a few weeks ago, I was informed that even though the season ended six months ago and I have not seen, nor communicated at all, with the captain, he continues to slander me to other crew members that he remains in contact with. A new male crew member just informed me that the captain recently told him that I had slept with all the male crew members last season and had even slept with a few passengers and that this new male crew member would more than likely be able to "have a turn" with me. These are all very false accusations. I have gone to the HR manager and the Admiral with this issue and, while they claim to be horrified and disgusted, the only repercussion the captain received was a 'stern talking to' from the Admiral. This captain, during the course of my one year with this company, has had sexual relations with three subordinates that I know of, and it disgusts me that the company who owns the boat continues to allow this happen. I'm wondering what legal action I might take against the captain, and against the company? At this point, I have no idea which direction to go, nor what steps to take.