If you’re Sergey Brin, Evan Spiegel, Jan Koum, Jeff Bezos, Laurene Powell Jobs, Eric Schmidt, Yuri Milner or any one of dozens of other modern-day tech moguls, it’s not enough to just own a yacht. Now you might need two—one for you and your guests to ride on, and one to act as a “support vessel,” tailing you around the seven seas while towing submersibles, seaplanes, helicopters or just some extra deckhands.

It’s the maritime version of keeping up with the Joneses. When it comes to accumulating pleasure craft, tech’s billionaire elite are sparing no expense—and that includes on submarines, the newest must-have add-on to the luxury superyacht, Titanic disasters be damned. Executives seem to bring the same cutthroat ambition to yachting that they do to business, sizing up each other’s yacht lengths, hiring the same small cadre of designers and tradespeople, and filling them with the same toys and tech.

“If you’re a billionaire, you want to have the nicest things because you can,” said superyacht designer Jonathan Quinn Barnett. “I think it’s actually a pleasure to know that if there’s anything out there, you own the finest.”