It turns out that Sheldon is the leader of a band of modern day pirates who are using Jack and his family to smuggle a cache of money and jewels. They order the Robinsons to turn over the yacht and leave in the lifeboat.
Sheldon is the leader of a modern-day pirate crew who are using Jack and his family to transport a stash of money and jewels. They demand the Robinsons hand over their yacht and depart in a lifeboat.