4e:Overworld Battles
A set of variant rules for more involved use of vehicles, especially (but not limited to) seagoing ships.
In addition to the standard battle grid, where each square is five feet to a side, there is now the overworld battle grid, where each square is fifty feet to a side. This means a typical vehicle is capable of fitting in 1-by-1 square, and acts for all intents and purposes like a Medium sized creature. The crew and passengers of these vehicles are on a different scale and thus not represented on the overworld battle grid.
All vehicles being piloted or commanded by the players will move at the direction of the players, but on each vehicle's own initiative. That initiative may be bolstered by the player characters, however. It is only when the action shifts to the smaller scale – such as when a ship is boarded, encounters a creature, or is otherwise intercepted – that the players will roll initiative for their players.
Example of Play
The player characters are crewing the dwarven longship Queen Anvil's Revenge, sailing through the icy waters of the Great Silent Sea. There are a number of icebergs nearby, many of them far larger than the ship itself, making the route treacherous. Suddenly, out from behind one of the icebergs emerges black sails and a sleek profile: it's the pirate vessel called the Laughing Coffin, with the mad captain Abraham Graves at the helm.
Aboard the Revenge, the cannons are manned and a volley is sent toward the Coffin, before turning away (a standard action to attack at range, and then a move). The Coffin ignores the chance to return fire, instead forging ahead with full sail, Captain Graves gripping the wheel in his undead grip (double move action). Another volley from the Revenge does nothing to deter the lich pirate, or his crew of howling skeletal goblins, and the Coffin smashes sidelong into the Revenge, with grappling hooks securing both vessels together.
The focus of the action switches from the overworld back down to the regular battle grid, where the two ships and the surrounding ice-filled ocean now create a 30x30 area of complex terrain.