Half-Safe by James Nestor

"It had been four full months since Ben and his wife, Elinore, steered the tiny amphibious jeep they called Half-Safe into the frigid waters of Halifax Harbor and headed east toward Africa. It was the first time anyone had tried to circumnavigate the world by land and sea in a single vehicle, let alone one that was eight times smaller than any motorized boat that had ever crossed the Atlantic. It was a harebrained scheme, and the Carlins knew it. That was the point."