Looks like a lot of fun!
Innerspace Productions, develops customized high performance submersible watercrafts called Seabreachers. Founded in 1997 by Rob Innes (a New Zealand boat builder) and Dan Piazza (a machinist), the vessels can go up to 40mph on the surface and 20mph under water. Because they are positively buoyant, the vessel cannot sink. When diving too deep, the engine will immediately lose power and the craft will float back up to the surface. The watercraft can jump, dive and roll much like the sharks and dolphins they were designed to mirror.