根据以下内容，回答下列各题。

In the old days, divers used to go down into the sea looking for ships that had sunk, because they hoped to find gold and jewels．Now divers still search for valuable things in sunken ships, but they also try to bring to the surface the ships themselves, or parts of them．The value of different kinds of metals has increased greatly over the last twenty or thirty years and even though a ship has been under the sea for many years, it may be worth a great deal．

One famous sunken ship is the “Lusitania”, which sank off the southern coast of Ireland in 1915 with a loss of nearly, 1,500 lives．It has four huge propellers made of an expensive metal．Today each of those propellers is worth $ 300,000 or more．The ship lying on the sea-bed has been brought by a man called John Light．He paid about $ 1,200,000 for the whole ship．He hopes to bring up those propellers and sell them．He also hopes to sell other parts of the ship, when he has brought them to the surface, for about $ 600,000．

Divers today try to bring to the surface _______．