Mr. Howell's Secret
I think the Mr. Howell set it up, and Ginger was in on it. Note that the Howell's brought seemingly all of their worldly possessions, not to mention millions in cash, onto a boat that was meant to be at sea for only 3 hours. Ginger, too, brought a massive wardrobe with her. Meanwhile, the other 4 only have the clothes on their back.
My suspicion is that Mr. Howell planned to hijack the ship. Mrs. Howell was in on it, but unaware that Thurston intended to kill her along with the other passengers, except for his secret mistress, Ginger. Mrs. Howell thought the two of them were going to run off together, but in fact Thurston and Ginger were going to abscond to some tropical country without an extradition policy.
Things went awry in the storm, and his plan never came to fruition, and he ended up shipwrecked with the lot of them.