Lexus thinks it finally has a way to catch up with Mercedes in luxury-car sales: go into the high-end boat business.

Toyota Motor Corp.'s premium brand plans to start selling a 65-foot (20-meter) ultra-luxury yacht in the U.S. in the second half of next year. The vessel, announced at a boat show last week in Yokohama, will have room for 15 guests, three bedrooms with their own washrooms, plus separate quarters for crew. Executive Vice President Shigeki Tomoyama would not reveal the boat's price, but said it will be comparable to others in its class. (Sunseeker's 66-foot Manhattan goes for about $3 million.)

For Lexus, taking to the water is less about selling big, beautiful boats — the market is tiny — than it is about adding luster to a brand that's lost some of its shine. Lexus has not held the lead in high-end U.S. car sales for almost a decade. Meanwhile, mass-market automakers are closing the quality gap and the shift toward autonomous driving and vehicle-sharing threaten to turn cars into utilitarian people-movers.