Treasure, a Sailor's Siren

A fellow approaches you and says, “I know where there is a sunken pirate treasure ship right here off the coast. Would you be interested in helping me for a fifty percent partnership?”
He claims he heard a voice of a spirit asking for help and promises of great treasures. You dive on the site and find a large lump of corroded Spanish pieces of eight, worth many thousands. Dragging it up on deck you encounter a manifestation of a pirate spirit who spelled it out, no help, no treasure then he disappears along with the lump of ancient silver coins.
Three individuals pool their funds to search a suspected underwater ancient treasure site and find more than they bargained for with a pirate’s spirit demanding assistance in crossing over into a repentance afterlife. In assisting the spirits they find favor with other successful salvors and their allies, the US Navy who help keep them out of danger from modern day pirates and drug runners