In The Swiss Family Robinson, how does the family end up on the tropical island?

The Robinson family is traveling on board a sailing ship when, suddenly, they're caught in the middle of a terrible storm. The rest of the ship's passengers evacuate the ship, abandoning the Robinsons to their fate. Thankfully, they manage to survive a particularly rough night at sea. When the morning comes, they spot a desert island in the distance. That's when the Robinsons display their remarkable ingenuity. They scout around the ship to see what they can find. Eventually, they manage to locate some tools. They then set about making eight large tubs out of casks sawed in half. William Robinson then nails a couple of planks to hold the tubs together. This is the impromptu raft that the Robinson family uses to make its way to the desert island.