A ferry is a vessel designed for the transportation of passengers and/or vehicles, generally being a waterborne extension of road or pedestrian networks. As such, ferrys tend to operate over limited distances (i.e., they tend not to cross oceans - like liners). Smaller, passenger-only, ferries are known as water taxis. A ferry which includes the amenities of a cruise ship is known as a cruiseferry, popular on Baltic routes.
As an extension of, primarily, road networks, ferry services carry some of the highest-value cargo. As such, arrival times are extremely-important: Passengers expect the fastest possible service. Vessels often transit near the highest speed the route and cargo volume will allow. Additional power is often fitted to vessels on longer routes, allowing a vessel subjected to heavy seas or delays to make up time and maintain its schedule. Interestingly, increasing environmental concerns may actually slow some ferry routes - as environmentally aware passengers become more conscience of their carbon footprints.
Typically, ferry passengers have different expectations than cruise-ship passengers. For short routes or foot routes, there may not be any amenities beyond a water closet; however, as routes get longer, snack bars, vending machines, hot coffee, food services, accomodations, child care, entertainment, bars, tourist information, gift shops and even casinos become desireable. The level of outfit need not be as high as a cruise ship (aside from cruiseferries), as passengers are often using the ferry as a low-cost alternative to toll-bridges, long alternative routes, or aircraft. It is desirable for the hullform to have comfortable roll characteristics (which may require active measures), as passengers are unlikely to be seafarers.
One major concern for the design of ferries is the vehicle decks. These long, mostly unbroken decks can produce a large free-surface effect with relatively minimal water collection. The lack of transverse divisions produces rapid flooding along the length of the vessel if any portion of the deck is submerged. It also requires the bulkhead deck to be lower than the cargo areas, which may limit the amount of reserve bouyancy in the hull.
Before a ferry can be designed, it is essential to determine what the mix of passengers and vehicles will be, in order to maximize economy. The type and number of vehicles will determine the amount of lane-meters required, and the number of passengers (walk-on, bus, car, trucking) will determine how much public space and accomodation will be required. There are passengers for whom it may be beneficial to seperate spaces: truckers, for example, might appreciate a seperate lounge, shower facilities, and may desire higher-density (cheaper) accomodations.
Port requirements can vary from a simple wharf or beach for foot passenger service, to a marginal quay for quarter ramps, to custom-built single or double ramp arrangements. Larger ferries on busier routes will require more intricate systems of queueing, ticketting, loading, and unloading of traffic. With high levels of passenger service, shore based terminals are common - including food, entertainment, and even accomodations for people waiting for the next run. Port facilities will be a big driver in the design of a ferry. The vessels particulars will be constrained by the ports limits for draft, length and breadth. Currents, winds, tides, access channels, and requirements for assistance may preclude some designs or require installation of thrusters. Ice conditions may require suspension of ferry services in winter months, or require the ferry to have an ice class.
Ferries, as transportation links, are the ship type perhaps most identifiable with the general population, as they are the ship type the public is most likely to travel on. For many destinations, the ferry is a principle mode of arrival for tourists, and in this role they may be seen as the first welcome to an island, area or country. Ferries can become local symbols, i.e., the Kalakala to the people of Seattle.