Convenient Escape Boat

The bad guys are on your tail! There's nowhere to hide, nowhere to go... but if you're anywhere near a body of water, don't worry: Guaranteed, there's a Convenient Escape Boat about to leave the dock. Just run a bit faster, hit the edge of the wharf, and jump onto that bad boy! You'll be safe at last, and if you're lucky, your pursuers will try and follow... and end up swimming back to shore, shaking their fists all the while.

This also counts if you drive off a bridge and a barge shows up below. Very rarely is the subject of how the escapee gets off the boat addressed-- they might end up swimming back to shore, too. Sometimes justified by having the pursuers cuss about how their quarry not only got away, but stole their boat as well.

Often subverted by having the jumper land on the boat, only to discover that the boat is pulling in, not out. Closely related to its action-movie brethren Roof Hopping, Trash Landing, and Train Escape. Car examples may include a Ramp Jump.

Examples of Convenient Escape Boat include:

Anime and Manga

Pokémon 4 Ever used this at the beginning when Ash tried to catch a ferry.
Greenback Jane arc of Black Lagoon features such an emergency escape. Only some of the pursuers manage to follow.

Comic Books

This happens to Ethan and Skink the first time they escape the Raven castle in Scion.

Film

Remy the rat in Ratatouille escapes from an evil chef by jumping on a boat. The chef manages to catch the first one, but he doesn't make the second.
This happens in White Lightning, and inspired a similar act in The Simpsons (see below)
Happens in In Bruges when Colin Farrell's character is attempting to outrun Ralph Fiennes, the boss of his crime syndicate.
Dawn of the Dead does this... though It Doesn't End Well
This is done somewhat in the movie The Lord of the Rings, when the Nazgul are chasing the hobbits—and the hobbits pull off in the ferry, before Frodo even gets there. Naturally, Frodo has to jump for it—and makes it... just in time. (In the book, it was nowhere this dramatic; the Nazgul follows them to the river, but is unseen until long after they've pulled off).
This is also done in the movie Some Like It Hot, where Jack Lemmon's "Fiance" just happens to be there waiting for him in a boat.
This is how Sun Yat Sen escapes the authorities at the end of one of the Wang Fei Hong movies.
Indiana Jones and the Last Crusade
- Subverted while Indiana and Dr. Schneider are fleeing members of the Brotherhood of the Cruciform Sword. They find a boat and try to escape, but the Brotherhood members also find boats, pursue and catch up to them.
- Invoked when Indy and his dad are trying to escape Castle Brunwald. They find several boats and Indy acts like he's going to use one of them to escape, fooling even his father. However, he's really trying to trick the Nazis into thinking they used the boat: he actually plans to escape using a motorcycle with attached sidecar.
Parodied in 50 First Dates when Adam Sandler's character pretends to be a CIA agent, he leaps off the dock and onto some guy's jet ski. He bribes the guy to just keep driving as if this was normal.

Literature

In Watership Down, a group of rabbits manage to pull this off, though the author quickly comments that it worked mainly by chance and circumstance.
In the first (of many) Dragonlance trilogies. Too bad the dwarf had a fear of water.
In Horatio Hornblower, the title hero and his some of his best sailors are captured and taken into France for a show trial and execution. While they are being transported, they stop near a river with a convenient row boat available. Being Badass Sailors, they are able to work out an escape once they have access to a boat and water.
Played with in Sweet Silver Blues, twice. The first time, Garrett gives a thug the slip by running out to the end of a dock and onto a ship, then keeps going off the ship into the water. The thug backs off rather than encounter the Crown agents whose ship it is. The second time, Morley plays this trope straight as he runs along the dock to the ship that's taking him and Garrett home ... only he's arranged for his pursuer to be nabbed by those same Crown agents who are waiting in ambush at the dockyard.
Subverted in The Fifth Elephant, in which the very clever werewolves have one of their pack waiting on board the Convenient Escape Boat.
The absence of one of these is a source of profound shock in The Pyrates. As Colonel Blood says:

"Whoever heard o' pirate ship without a small boat moored 'neath the stern an' provisioned wi' all necessities, so that fugitives can light out unseen!"

Time Scout: During one of his many escapes, Skeeter ends up in the Tiber. Fortunately a boat happens to be right at hand. Also, a Convenient Escape Horse, in that as soon as he gets out of the water he happens upon a champion racing horse.
Happens repeatedly in Tim Dorsey's Serge Storms novels, although sometimes Serge arranges things in advance, as in Electric Barracuda.

Live-Action TV

Psych: In "You Can't Handle This Episode" Juliet's secret-agent brother Ewen is introduced by having him jump obstacles and dodge bullet fire while being chased. He runs onto a public beach, jumps into the water, knocks a civilian off of a Jet Ski and zooms off to safety. All while having a conversation Juliet on the phone.

Video Games

In Left 4 Dead it happens once in each game. In the first game it happens in the second scenario after the characters find the town that you spend the first couple of chapters trying to flee to has already been overrun and they decide to head to the river.
In Grand Theft Auto, you can often rely on a boat being near water to help you make an easy escape. An example is The Snow Storm in GTA IV, where after you fight your way out of the hospital you can continue to push through the police on land, or take the easy route and jump in a nearby boat.
- The same game has a mob boss pull this stunt, forcing you to chase him along the coast on a bike (good thing he didn't think to travel out to sea...)
- III and Vice City had the problem of 'instant drowning', which made leaving the boat problematic. The hero of San Andreas could swim (and nobody else could) so often just leaping out into open water was a viable escape strategy. And funny, if anyone tried to follow.
Played straight in the first level of Prince of Persia: The Shadow and The Flame.
Somewhat inverted in Time Crisis, as it's one of the Bad Guys who escapes this way, and you have to give chase on your own motorboat.

Web Comics

In The Dreamer, Alan and Beatrice escape Gen. Howe's ship by boat.

Western Animation

The Simpsons did it several times. On one occasion, Homer is trying to escape his guilt at not giving his dad a kidney, so he hops onto a departing ship full of "lost souls."
- They also did it in "Homer the Heretic": The Flanders family is chasing Homer in their car, so Homer heads to Springfield Harbor. He drives off a pier, landing on a garbage barge. The Flanders' hit the brakes, almost falling into the water. Homer waves back at them, then asks the captain where the barge is headed. "To Garbage Island," he replies. This is apparently a reference to the film White Lightning.
- They also invert is with the Show Within a Show Knightboat. The boat always has a canal or inlet that it can follow when enemies try to escape by going inland.
  - Lisa: "Or a fjord."

Real Life

One of the tests in the SOE course was to anchor a MacGuffin in a pond, show a team some random material that can be built into a raft and tell them to fetch the Macguffin (It sounds like whoever was in charge of that thing at the time, thought he was teaching boy scouts not aspiring assassins). Just to mess with people they always left a completed raft buried under some brush to see if anyone was Genre Savvy enough to look somewhere else.