This sounds like the stuff that severe seasickness is made of:
He calls it a vertical torpedo. The axis of his 24-foot-long craft is upright rather than horizontal, speeding the plunge. His goal is to fall and rise as quickly as possible so he can maximize his time investigating the dark seabed. He wants to prowl the bottom for six hours. …
Just as bullets are spun to steady their flight, Mr. Cameron’s craft rotates on its vertical axis — another first. In a test dive, he has already broken the modern depth record for piloted vehicles, going down more than five miles.
Read more here on The New York Times