Beyond the Poseidon Adventure (1979)

"Before her fate is sealed by the deep, the superliner Poseidon will reveal one last secret."

After "The Poseidon Adventure", in which the ship got flipped over by a tidal wave, the ship drifts bottom-up in the sea. While the passengers are still on board waiting to be rescued, two rivaling salvage parties enter the ship on search for money, gold and a small amount of plutonium.