Ship-Shape Shipwreck

So you're looking for a lost treasure ship on the bottom of the ocean. Good thing that the ocean is a perfect preservative. Oh, it might have some barnacles and coral here and there, maybe some parts have collapsed, but that may have happened when it was sunk. Heck, it probably still has tattered sails! It'll be sitting slightly to one side, but still mostly upright.

Not so in the real world. In the real world, water, particularly salt water, and especially warm salt water as seen in most pirate-frequented areas, wreaks havoc on anything immersed in it for too long. Just look at the continued decay of the Titanic or ships sunk during World War II. A wooden ship in salt water would be shipworm bait in no time flat.

Often an excuse for a Gang Plank Galleon; ubiquitous in the Derelict Graveyard. Can also be a Ghost Ship.

Comic Books

 * Averted in Red Rackham's Treasure, where the wreck of the Unicorn has decayed considerably.

Film

 * In The Goonies, One-Eyed Willie's 350-year-old pirate ship actually sails out onto the open seas at the end. While the ship is not submerged, it has been sitting in water for three centuries in a wet, brackish cavern with lots of moisture dripping from stalactites. Aside from the skeleton of Willie, the ship and even its sails appear to be in fairly good condition.

Video Games

 * In Donkey Kong Country 2, there's a pirate ship sitting in lava.
 * In Final Fantasy X, the Al Bhed retrieve the Global Airship from the bottom of the sea, where it's been for a thousand years. And they get it working. The continued existence of lots of Machina a millenium after the production thereof was banned implies that the ancients really built to last.
 * Monkey Island 2: LeChuck's Revenge.
 * Hostile Waters makes an effort to play this as straight as possible while also subverting it. Antaeus Cruiser 00 is in remarkably good condition after spending 20 years on the ocean bed. It manages to surface and set sailing just fine despite the long rest. Thankfully, nothing essential got damaged too badly, so after a visit in a dry dock the ship is at (or at least, near) full operational capacity, though they are signs she never gets as good as new. 00's sister ship, 04 isn't as lucky. She doesn't wake from her nap on the ocean bed. They justify this through the use of advanced nanotechnology. Both 00 and 04 have creation engines on board with trillions of the little things, which would have repaired 04, too, if it had received the signal.

Western Animation

 * In Atlantis: The Lost Empire, there's a Greek trireme in perfect condition on the ocean floor.
 * Futurama shows a pirate ship at the bottom of the ocean a thousand years from our present time.
 * Granted, Bender burns down a conch shell on the sea floor in the same episode.
 * The climax of Disney's The Little Mermaid had Ursula control the weather and raise a veritable fleet of derelict wooden sailing ships. Prince Eric is even able to gain control of one and steer it.
 * In Teen Titans, they explore a perfectly-preserved shipwreck to look for missing toxic waste. However, it had only been sunk the previous night.

Real Life

 * The Vasa, a fine example of royal idiocy, sank in the harbor in 1627. Said harbor is in the Baltic, an in-water sea that's brackish rather than seawater salty and is therefore free of the shipworm. The ship was salvaged in 1961 and is on display.
 * Thanks to mitigating factors including a shorter time frame and the cooler waters of the English Channel, a Sherman tank known to have fallen into the ocean during the D-Day invasion was salvaged for the 50th anniversary commemoration. It cleaned up nicely enough to fire live rounds. For "decades of seawater" levels of "cleanup."
 * The Dead Sea, on the other hand, is so salty that it preserves things due to the fact that very few things that would eat away at wrecks survive. A relatively recent expedition unearthed an ancient wooden ship in almost perfect condition.
 * The Great Lakes are fresh water so the wrecks of ships, even those of wooden sailing ships a couple of centuries old, are amazingly well-preserved.
 * The Black Sea has two distinctive layers. The deeper layer is very anoxic and nothing can live in it. Ancient ships that sunk near or under that layer—as well as signs of settlements from when the Sea was a freshwater lake—are found almost perfectly preserved.