Past over due compensation options?

Part of the answer depends on the nationality of the owners, the nature of the legal entity owning and the flag of the vessel.

Depending on those items, I suggest a lawyer notifying them of intent and of possible consequences of not paying. Seldom will you be forced to sue, but if you are, then you'll make it as inconvenient on them as possible. If it's an amount you can sue for in small claims court, then all the better. If the total of all crew exceeds the limit of small claims then each file a separate suit.

Depending on all the details, the owner might be shocked at the power you have and what can happen. First thing is a brief meeting with an attorney who can give you the facts as they are specifically in your situation. So many variables including Labor Dept (wage and hour), possible arrest of vessel, liens, double and treble damages.

I looked at a 123' that had a marshalls sticker on it. When I inquired, the broker said the captain had sued and rec'd judgement for past wages. And of course th owner disagreed and appleaded. Thus the sticker.

Maybe just one of those stickers made and slap it on the boat! That will get his attention. ( Actually don't do that, just joking)

If the boat is at a dock, hire a diver and take the props off.
(It has been done in Fort Lauderdale)
Legal? No idea, but probably effective.

Done here in jax to keep a yacht from skipping out on a yard tab.
Everybody & their mother knew it was going to happen.

Judge ordered the wheels re-installed.

2 days later, the yacht did bug out.

If USCG documented; file a lien with the CG. and ownership cannot be transferred until cleared, unless someone wants to buy an encumbered title. There is no automatic notice sent to the owner, but you should do that yourself. Sometimes, that's enough.
Instructions here