World War I completely disorganized the Atlantic Ferry and in 1918 removed German competition. At that time Germany had three superliners, but all were taken as war reparations. The Vaterland became the U.S. Line's Leviathan; the Imperator became the Cunard Line's Barengaria; and the Bismarck became the White Star Line's Majestic. That war severely cut traffic, although ships were used for troop transport. By eliminating German competition and seizing their great ships, the Western Allies returned to competing among themselves.
During the prosperous years of the 1920s, tourist travel grew rapidly, calling forth a new wave of construction, beginning with the French Line's lle de France in 1927 and gaining fiercer competition when the Germans returned to the race with the launching on successive days in 1928 of the Europa and the Bremen. But by the end of 1929 the Great Depression had begun; it made transatlantic passage a luxury that fewer and fewer could afford and rendered immigration to the United States impractical
Because the international competition in transatlantic shipping reached full stride only with the return of German ships in 1928, major decisions as to construction were made just as the Great Depression was beginning. Since the beginning of the century the "1,000-foot" ship had been discussed among shipowners and builders. A new Oceanic was planned in the late 1920s but abandoned in 1929 because its engines seemed impractical. In 1930 the French Line planned a quadruple-screw liner of 981.5 feet, which would represent another and, as it turned out, the final -ratchet in the expansion of the passenger liner. What came of that undertaking was the most interesting, and by wide agreement the most beautiful, large ship ever built. The Normandie was the first large ship to be built according to the 1929 Convention for Safety of Life at Sea and was designed so the forward end of the promenade deck served as a breakwater, permitting it to maintain a high speed even in rough weather. The French Line had established a policy with the lle de France of encouraging tourist travel through luxurious accommodations (changing from third class, which was little more than steerage with private cabins, to tourist class, which was simple but comfortable). The Normandie offered seven accommodation classes in a total of 1,975 berths; the crew numbered 1,345. The ship popularized a design style, Moderne, that emulated the new, nonhistorical art and architecture. The bow was designed with the U-shape favoured by the designer Vladimir Yourkevitch. Turboelectric propelling machines of 160,000 shaft horsepower allowed a speed of 32.1 knots in trials in 1935. In 1937 it was fitted with four-bladed propellers, permitting a 3-day, 22-hour and 7-minute crossing, which won the Blue Riband from the Europa.
To compete with the Normandie, in 1930 Cunard built the Queen Mary, which was launched in 1934. At 975 feet, it was Britain's first entry in the 1,000-foot category. The ship was never so elegant as its French rival and was a bit slower, but its luck was much better. The Normandie burned at the dock in New York in February 1942 while being refitted as a troopship. The Queen Mary was the epitome of the Atlantic liner before being retired to Long Beach, Calif., to serve as a hotel.
During World War II civilian transportation by sea was largely suspended, whereas military transport was vastly expanded. Great numbers of "Liberty"' and "Victory" ships were constructed, and at the close of the war surplus ships were returned to peacetime purposes. A sister ship of the Queen Mary, the Queen Elizabeth (at 83,673 tons the largest passenger ship ever built), was launched in 1938, but the interior had not been fitted out before the war came in 1939. First used as a troopship during the war, it was completed as a luxury liner after 1945 and operated with the Queen Mary
until the 1960s, when the jet airplane stole most of the trade from the Atlantic Ferry
Experience with the two Cunard liners in the years immediately after 1945 suggested the value in having two giant ships, of approximately the same size and with a speed that allowed a transatlantic run of four days or less, so that one ship might sail from New York and another from Europe weekly. This competition began when U.S. Lines launched the 53,329-ton United States. Though lighter than the Queen Elizabeth, greater use of aluminum in the superstructure and more efficient steam turbine engines allowed it to carry essentially the same number of passengers. The great advantage lay in its speed of 35.59 knots, which captured the Blue Riband from the Queen Mary in 1952, an honour the latter had held for 14 years.
The history of other merchant marine activities parallels that of the great passenger liners. Freighter navigation, tanker navigation, naval ships, and the more recent near replacement of bulk cargo by container transport must be understood as a similar ever-improving technology. Iron followed wood as a construction material and was followed in turn by steel. Until very recently steam was a source of power, though the diesel engine was used for some ships as early as the Vandal of 1903. After 1900 there was a general division between the use of steam turbines in passenger liners and diesel engines in freighters. Europeans, particularly the Scandinavians, favoured the diesel internal-combustion engine, with its more economical fuel consumption, whereas American shipping companies tended to favour steam turbines because their labour costs were usually lower. The rapid rise in the cost of petroleum fuel after 1973 led to increased diesel-engine construction.
A commercial ship is usually a link in a "trade route" between distant points. Goods flowing in the route must be transferred to and from the sea link; they must also be given care while aboard the ship, and in turn they must not be a hazard to the ship and its crew.
Ancient cargo handling consisted almost exclusively of manually carrying cargo in single man-loads. For example, grain would be packed into sacks, each of a size that a man could carry on or off the ship on his shoulders. During the many centuries of dominance by sailing vessels, this process might be supplemented by hoisting with the ship's running rigging.
A line reeved through a block on the end of a yard might be led to a capstan by which a group of men might develop the force needed to lift an object far heavier than a single man-load.
Steam propulsion brought the steam winch and rigging that was intended solely for lifting cargo. The near-universal practice as it developed into the 20th century was to fit at least one pair of booms to serve each cargo hatchway, with each boom supported by rigging from a "king post," a short, stout mast whose sole function was boom support. Winches were mounted at the base of the king post. In action, the head of one boom would be rigged in fixed position over the hatchway; the head of the other would be rigged over the cargo-handling space on the pier alongside. A single lifting hook would be used, but a line would lead from the hook to each of the two boom-heads ("married falls") and thence each to its individual winch. By cooperative tensioning and slackening of the two lines, the winch operators could cause the hook to move vertically directly beneath either boom-head or horizontally between them. Cargo was thereby moved between cargo hold and pier with no gear movement save that of the hook and its two supporting lines. This scheme is known as burton ing
Burtoning was gradually replaced by systems better adapted to special cargoes. It remained in favour only for handling very heavy objects, so that the few ships that were built during the late 20th century for this type of cargo were usually fitted with at least one set of massive burtoning gear. The first cargo to require a unique handling system was petroleum. When first carried by sea, petroleum products were packaged in barrels that were handled in the traditional way, but the great volume to be moved quickly soon made this method of packaging and handling woefully inadequate. Since the late 19th century crude oil and its many products have been transported in bulk - i.e., without packaging. The hulls of tankers (as described above; see Types of ships: Tankers) are subdivided into a number of cells, or tanks, into which the liquid cargo is pumped through hoses by pumps mounted on the shore. Unloading is effected in the reverse manner by pumps mounted within the ship. Usually the only external cargo-handling gear is a pair of cranes or boom-post winch sets (one for each side of the ship) for handling the rather massive hoses that connect ship to shore facility.
The handling of many other commodities is more economical if done without packaging and with at least some of the continuous-flow features of pumping. For example, the loading of "dry bulk" commodities such as coal, ore, and grain is nearly always done from special shore facilities that pour them from a high elevation directly into the cargo holds of the ship.
Although the ship may be designed for the commodity, almost any cargo-carrying ship except the tanker can accept dry-bulk cargoes in this fashion.
Discharging dry bulk is another matter. It can be lifted from the holds by grab buckets, but conventional burtoning gear is ill-suited for the operation of these devices. For this reason cargo terminals that receive bulk cargo are often equipped with unloading cranes that are especially suited for grab-bucket operation or with vacuum hoses for moving low-density cargo such as grain. Special-purpose dry-bulk ships may therefore be without onboard cargo handling gear (see above Types of ships: Dry-bulk ships). Examples are the ships built before 1970 to carry iron ore on the Great Lakes of North America.
Since 1970 all such ships built for Great Lakes service have been fitted with their own unloading gear, and their example has been followed by many oceangoing carriers of dry bulk. The handling gear usually consists of a series of three conveyor belts. The first runs under the cargo holds, whence it may receive the cargo through hopper doors in the bottom. The second belt receives the cargo from the first and carries it to the main deck level of the hull. There it discharges to the belt that carries the cargo to the end of a discharge boom, whence the cargo is dumped onto the receiving ground ashore. The discharge boom can be slewed and elevated to reach the appropriate discharge point. A continuously acting onboard discharge system of this type can attain much higher discharge rates than grab buckets, and it avoids the damage to hull surfaces that is inevitable in bucket operation. Further, it gives a ship the flexibility to serve points that are not fitted with unloading gear.
The economic burden of handling nonbulk (or "break-bulk") cargoes in small batches is less evident than with cargoes that can be pumped, poured, or conveyed, but it was making itself very evident as early as the 1950s. The revenue lost from keeping a ship in port while it was slowly -and at high labour cost loaded or unloaded was one factor; another was the inherent labour-intensiveness of moving cargo horizontally in order to reach the hoisting gear and then loading and unloading rail cars and trucks at pierside. By I960 these factors had led to the introduction of standardized steel or aluminum containers 8 ? 8 ? 40 feet in the most common size -into which almost any nonbulk commodity could be stowed. The primary advantages in containerized shipping are the radical reduction in the number of cargo pieces to be handled and the high degree of protection the containers provide to the cargo items. Further advantages come from designing ships specifically for carriage of containers, shoreside terminals for their rapid transfer, and land vehicles for their carriage. These additional
steps were put into place quite rapidly after the container concept was introduced.
The essential feature of container ships is a width of hatchway that allows the containers to be handled solely by vertical lifting and lowering. This feature is usually supplemented by vertical guide rails that divide the cargo holds into cells that are sized precisely to hold stacks of containers. Labour within the hold is thereby reduced to insignificance. A consequence of great value is the freedom from "dunnage," the packing and bracing necessary to immobilize the usual odd-sized nonbulk cargoes. The highway trailers and railcars that form the land part of the trade route are similarly designed to fit the container, thereby making the shoreside handling rapid and virtually free of hands-on labour. Cranes and lifting gear designed for handling the standard-size containers are the third part of the rapid and economical ship/shore transfer. Cranes best-suited to this service are usually too massive for shipboard mounting and, hence, are part of the terminal. Typical container ships are therefore not fitted with cargo handling gear (see also above Types of ships: Container ships).In loading or unloading a barge-carrying ship, no shore terminal or any special shore vehicle is required, since delivery to or from the ship is by water. Where the seaport is at the mouth of an extensive river system, the ultimate terminus can be at a great distance from the ship. Points not adjacent to a navigable waterway can be served as well, although an extra step of transfer to or from a land link is required.
When the cargo has wheels - e.g., automobiles, trucks, and railway cars the most satisfactory cargo handling method is simply to roll it on and off. Vehicle ferries have been familiar in many waters for many centuries (see above, Types of ships: Ferries), and the growth since about I960 of an extensive international trade in motor vehicles has led to an extension of the ferry principle into roll-on/roll-off ships, which carry automobiles strictly as cargo yet load and unload them by driving them on their own wheels. Ships built for "ro-ro" traffic are fitted with doors in the hull (most often at the ends), internal ramps and elevators for deck-to-deck transfers, and external ramps to join the hull doors to the pier. Often the main or only door is in the stern, facing directly aft and fitted with a massive folding ramp exterior to the hull. The ramp is often equipped for slewing - i.e., rotating so that it can be landed on a pier alongside the ship.
Although many types of cargo are handled by gear that is designed for a particular type, general-purpose equipment retains a niche. However, the traditional burtoning gear has almost disappeared among new buildings in favour of cranes that are adapted from shoreside lifting machinery. This
alternative is usually less costly to build and maintain, and it requires less labour in operation.
The enormous increase in the marine transit of materials in bulk, with petroleum leading the way, has given rise to the development of special terminals for the loading and discharge of such materials. The principal factor influencing the design of these installations is the still-increasing size of the ships. A single example of the effect of this change on design limits will be sufficient. The "Queen" liners, long the world's largest ships, never drew more than 42 feet of water. Supertankers, on the other hand, when fully loaded, draw up to 72 feet. If these ships required berthing structures of the type provided for conventional cargo and passenger liners and if the formula relating the capital costs of such structures to the deepest draft were applied, the cost of building an appropriate berth for such a tanker would reach a figure more than six times the cost of the Queen Mary's old berth. Fortunately, the high mobility of the cargo renders such drastic and expensive measures unnecessary. Heavy capacity access for individual shore-based vehicles to carry away the cargo is not required nor does the provision of services for the relatively small crews who man these great ships present any problem. The berthing positions can therefore be sited well out from the shore in deep water, and the structure itself can be limited to that required to provide a small island with mooring devices.