Building a deep-diving submarine: Flotation

Four teams are diving to the deepest part of the ocean, the Mariana Trench, which lies 11km (7 miles) down in the western Pacific.

One of them is DOER Marine, a marine technology company based in San Francisco.

They are currently putting the finishing touches to the design of their Deep Search submersible.

Here, Liz Taylor, who runs the company, explains why ceramics are the key to making sure that the sub can sink or float.