As an uninspected vessel, apparently OSHA has some say. However, from the OSHA web site:
OSHA does not have a regulation that addresses smoking in the workplace except for a limited number of regulations that address smoking and other sources of ignition from a fire safety perspective.
https://www.osha.gov/node/57108
If you can find a lawyer willing to take your case on a contingent fee, and advance all the costs, it may be worth suing your former employer. It might be a slam dunk case.
However, you may never be able to find another job in the Gulf, but that might be a good thing.
Before you get too far into this, was it a US flag vessel? I dealt with this too and because it was a Vanuatu flagged boat, I was SOL for using the smoke free workplace argument with the office.
Probably ironic since I’m a smoker myself, but the wheelhouse haze was too much even for me. 
Does the company have a smoking policy? I have seen such policies in the company’s SMS, if they have one, and explicitly stated even for those that didn’t.
Every company that does oil will have smoking in the TSMS. The policies are usually pretty restrictive especially when loading in oil terminals.
However given the selfishness of many smokers it may be best to find a non smoking crew or boat somewhere.