The size of ships also increases constantly because large ships are more economical than small ones. A freight steamer costing $500,000 and requiring a crew of 40 men will carry twice as much as two smaller steamers costing $600,000 together and requiring 50 men. Some modern ships have a " tonnage " of 50,000 tons and could carry over 100,000 tons of freight if they did not give up so much space to passengers. Such a ship is nearly 1000 feet long, 100 feet wide, and over 60 feet from the keel to the upper deck. It needs from 35 to 40 feet of water. For such steamers a shallow harbor, no matter how well protected, is useless. Practically no important ports, however, have natural harbors with any such depth. Hence each year millions of dollars are spent by the national government in order to deepen harbors, while cities and States also make appropriations for it. In a decade the national government has spent as much as ,000,000 on the improvement of the approaches to Philadelphia alone.
The Depth of American Harbors.—At present New York and San Francisco are the only American seaports having channels deep enough for great steamers drawing 40 feet. The people of Boston talk about a 45-foot channel to accommodate not only all present ships but the still larger ones that are expected in the near future. At present the Boston channel is 35 feet deep, which is practically the same as that of Philadelphia, Baltimore, Norfolk, New Orleans, and Seattle. Such important ports as Oakland and Los Angeles, where the original depth of part of the harbor was only 2 feet, and Galveston, have 30-foot channels; Charleston, 28; Savannah, 27, and Tampa and Mobile, 26. No other harbors in the United States have such deep channels. With the growing tendency to build large ships the more favored ports are bound to grow more and more at the expense of those with shallower channels.
(c) The Need for Roomy Harbors.—Deep water is needed not only in the channel but in places not far from shore where vessels can find room to anchor and turn around. A 1000-foot vessel needs nearly half a mile of free space in which to turn around, even though she has the help of tugs. When the great Imperator first came into New York Harbor the captains of some of the other boats in the North River did not realize how much room she required in order to turn and get into her berth in the dock. Consequently she bumped one or two other ships, ran into a wharf, and did such damage that her landing cost 5,000. Because of the large area required to maneu ver modern steamships a river such as forms the harbor at Savan nah is rarely so valuable as a bay along a submerged coast like that of the Atlantic from Norfolk northward, or the Pacific from Puget Sound northward.
(d) Dockage Space as a Necessity of a Good Harbor.—Harbors on submerged coasts not only furnish ample room, but also adequate dockage space. Liverpool, for example, on the estuary of the Mersey, where it has been easy to build many docks, has a great advantage over Shanghai, on the Yangtse delta, where ships have to discharge their cargo into lighters while at anchor in the middle of the river, five miles from the city. In bays formed by submergence the long shoreline and deep water close to the shore enable numerous docks to be built, so that steamers can be loaded directly from the land. It is an expensive thing when a ship costing a million dollars has to spend two-thirds of its time lying idle while waiting to come up to the docks, as has often happened at the oil port of Batum; the charges for interest and depreciation, that is, for wear, rust, breakage, decay, and old age, count up almost as rapidly as if she were carrying mer chandise, while the wages of the crew also continue. Hence ship owners prefer to send their ships to places where abundant docks make it possible to receive cargoes directly from warehouses or from railroad trains which come alongside, so that their loads may be hoisted from the cars to the ship's hold. Boston is an example of a great port which has suffered from lack of docks in the past, although now this is being remedied. New York, on the other hand, has perhaps the best dockage facilities in the world. Counting all the little bays and estuaries New York Harbor has a water frontage of 771 miles, 290 of which have been improved.
(e) How Land for City Building Affects the Value of a Harbor.—If a harbor does much business it must have a large city beside it. Such a city needs level land, especially for its business sections. Some cities such as San Francisco have grown great in spite of the hills, but those like Philadelphia, which have plenty of level land, are fortunate. So necessary is this that in many places shallow bays have been filled to make artificial land. The best residential section of Boston is the Back Bay, where once the tide ebbed and flowed. It paid Seattle to spend millions of dollars to cut down a steep hill of gravel in the heart of the city. By means of great streams of water squirted against the hill it was washed into the shallow part of the bay. Thus level land was obtained both by cutting down the hill and by filling the bay.