routes the freight taken by the carrier is billed at carrier's option as weight or measurement cargo; and oftentimes the charges are by article rather than by weight or measurement. Over some ocean routes freight is taken by weight and the calculation of the tonnage of different classes of freight and of special commodities would not require much time and labor; but, as regards most freight handled upon the ocean, the calculation involved in determining the tonnage of the several classes and of the special, or "ex-class," commodities included in a ship's cargo would be expensive and time consuming. This tonnage calculation to determine the tolls payable would have to be made either before the ship cleared from its port of departure, or would have to be made while the vessel was en route between the port of clearance and the Panama Canal. A ship's personnel does not include a clerical force, and it is probable that the practice would be to detain the ship at the port of clearance until the tonnage upon which tolls are to be paid could be calculated in the office of the company or of the agents controlling the vessel's movements. As is well known, the ship's manifest, in its present form, is the last paper taken aboard the vessel, and in order not to delay a vessel's clearance it is customary for the steamship company's office force to work overtime for one or more days in order to have the ship's manifest ready as soon as possible after the vessel's cargo has been put aboard. To make a tonnage calculation for the purpose of preparing a statement of the tonnage of different classes of freight as a basis for canal charges would so delay vessel movements as seriously to burden

ocean commerce.

(c) From the Government's point of view, cargo would be an undesirable basis for Panama tolls, because it would be practically impossible to detect and prevent fraud. A vessel presenting itself at the Panama Canal loaded possibly with hundreds of different articles could not be so inspected by the collectors of tolls as to check up the company's statement of cargo with the commodities listed in the ship's manifest or tonnage statement. It would be necessary for the canal officials to accept the sworn statement of the owners or master of the ship, and this would open the door to fraud. It is true that the Manchester Canal Co. derives most of its revenues from charges upon commodities, but this basis of charges is possible because the Manchester Canal includes the docks and warehouses at the ports of Manchester and other places along the waterway. In fact, the Manchester Canal Co. is both a canal and terminal company. Freight is loaded or discharged at Manchester and other canal ports, and the officials of the canal company can thus readily check the carriers' statements as to commodities loaded or discharged. In the case of such canals as the Kiel, the Suez, or the Panama, however, charges based upon commodities are administratively impracticable. The canals are merely transit routes where cargo is not transferred, loaded, or discharged. To prevent fraud in collecting tolls at transit canals, it is necessary to base the charges upon the ship rather than upon its cargo.

DISPLACEMENT TONNAGE.

Before discussing dead-weight tonnage, which is applied to the weight of cargo and fuel which vessels can carry, it will be best to explain displacement tonnage. The displacement ton is a unit applied to vessels and not to cargo, but in order to ascertain the dead-weight tonnage a vessel can carry it is first necessary to determine the vessel's displacement tonnage.

The displacement tonnage of a vessel is its weight in tons of 2,240 pounds avoirdupois, and is equal to the weight of water displaced by the vessel when afloat. Unless the term is qualified, the displacement tonnage of a vessel is the weight of the ship with its crew and supplies on board, but without fuel, passengers, or cargo. This is a vessel's displacement "light." The weight of water displaced by a vessel when loaded to its "deep-load line" is its displacement "loaded." The difference between the displacement tonnage of a vessel when "light" and when loaded to its "deep-load line" is its dead-weight tonnage, which is the maximum weight of fuel, cargo, and passengers that a vessel can carry.

A cubic foot of sea water weighs 64 pounds, or one-thirty fifth of an English long ton of 2,240 pounds avoirdupois. Thus the contents in cubic feet of that part of the vessel's hull

FIG. 27. DISPLACEMENT CURVE AND SCALE.

10

7 Light Draught

that is below the water line divided by 35 equal the vessel's displacement tonnage. If a ship were box-shaped—that is, if it were a parallelepiped-the product of its three dimensions in feet, its length, breadth, and its depth below the water line, divided by 35 would be the displacement tonnage; but, as vessel hulls are not parallelepipedons, the cubical contents of the hull of a ship have to be calculated by means of special mathematical rules, such as Simpson's rules or the trapezoidal rules.1

The ratio of the actual contents of the submerged portion of a ship's hull to the contents of a parallelepiped having length, breadth, and depth corresponding to the length, breadth, and draft of the ship is the vessel's "block coefficient" or its "coefficient of fineness." A fullshaped, slow freight steamer has a "block coefficient" of about 0.8-i. e., the submerged portion of the hull has a volume equal to 0.8 of the volume of a parallelepiped with equal dimensions. The "block coefficient" or "coefficient of fineness" of the average freight steamer varies from 0.7 to 0.75, while the coefficient of a combination freight and passenger steamer is about 0.65; that of a fast passenger steamer is about 0.6, while racing yachts may have a coefficient as low as 0.4. When the "coefficient of fineness" of a vessel is known, its displacement tonnage is determined by multiplying its length, breadth, and draft by its "coefficient of fineness" and dividing the product by 35.

In commercial practice it is desirable to know a vessel's displacement tonnage at any given draft between its "light" and "loaded" lines, for the reason that the difference between the displacement of a vessel "light" and the tonnage of its actual displacement indicates the weight of what the ship contains other than a crew and supplies. The displacement tonnage or weight of any particular ship at any given draft is shown by the vessel's "displacement curve" and scale. Figure 27 reproduces a typical displacement curve.

Figure 27 presents the displacement scale for a small vessel which draws but 7 feet of water when light, its displacement "light" being 550 tons. The vessel may load to a maximum draft of 14 feet, at which draft its displacement is 1,400 tons. The deadweight capacity of the ship is thus 850 tons. It may be noted in passing that the ship is permitted to be loaded, so that it has but 2 feet of freeboard, the freeboard being the distance between the level of the upper deck and the "deep-load line." Vessels engaged in the oversea trade would not be permitted to have such a small freeboard.

The figure also gives the ship's displacement curve. The curve is drawn as follows:

At the left the draft of the vessel and its freeboard are given in a perpendicular scale, which may be assumed to have been drawn to a scale of 1 inch to 1 foot. From the top of this vertical scale, a horizontal scale is so constructed that 1 inch equals 100 tons of displacement. By drawing horizontal lines through the points indicating the draft of the vessel at different drafts from zero to 14 feet and by drawing vertical lines through the points in the horizontal scale corresponding to the number of tons of displacement at various drafts from zero to 14 feet, and by drawing a curve through the points of the intersection of the horizontal and vertical lines, the curve of the ship's displacement is located. With this displacement curve known, the displacement of the vessel at any given point in its draft can be read off from the displacement scale.

ADVANTAGES AND DISADVANTAGES OF DISPLACEMENT TONNAGE AS A BASIS OF PANAMA TOLLS.

If displacement were made the basis of Panama tolls the charges might be placed either upon the vessel's displacement tonnage when loaded to the deep-load line, or upon its displacement tonnage at its actual draft, when applying at the canal for passage through the waterway. If the displacement of the vessel at its actual draft when passing through the canal were made the basis of the tolls, the charges would be levied upon the weight of the ship plus the weight of the cargo, passengers, and fuel it might have on board. The tolls would thus vary with the lading of the ship.

1 Mathematical rules for the calculation of the contents of the hulls of ships are explained, among other places, in Chapter X of the book Know Your Own Ship, by Thomas Walton, London, 1909.

Displacement tonnage would have the following advantages as a basis for canal charges: 1. It would be easy to determine the tonnage upon which tolls were to be paid. The vessel's displacement scale states its displacement tonnage at any draft up to the deep-load line, which represents the vessel's maximum draft. The displacement scale would indicate the number of tons upon which the vessel applying for passage through the canal would have to pay tolls.

2. Tolls based upon the displacement of a vessel at its actual draft would vary with the ship's lading, and vessels without cargo or with a light load would pay less than the ship would pay when fully laden. In the case of low-powered cargo steamers, the weight of a vessel when "light" might be half or less than half the weight of the vessel when fully loaded, and the amount of tolls payable by such ships would be largely affected by the extent to which the vessel's cargo capacity was occupied with freight. On the contrary, high-powered passenger steamers have relatively small capacity for carrying cargo. So much machinery and fuel are required to secure high speed that the weight of the vessel "light" will probably be at least three-fourths of its weight when loaded. In the case of fast passenger steamers, there is comparatively little difference in the weight of the vessel when its passenger and freight accommodations are unoccupied and when they are filled. Such steamers, however, constitute a relatively small share of the tonnage of the world's deep-sea marine. For most ships, tolls based upon the tonnage of actual displacement would vary materially with the lading of the vessels.

3. An advantage of minor importance which displacement tonnage would have as a basis for tolls would be that merchant vessels and warships would pay charges upon the same kind of tonnage. Displacement is the only logical basis for tolls upon warships, and if merchant vessels do not pay canal levies upon displacement, the charges must be levied upon two different bases. While the inconvenience resulting from this would be relatively slight, it obviously would be better to have a single rather than a dual basis for canal charges.

The disadvantages resulting from the adoption of displacement as a basis for canal charges upon vessels of commerce outweigh the advantages, and may be briefly stated as follows:

1. Unless actual displacement were made the basis of canal charges, every vessel would be obliged to have marked upon its hull by official action of the appropriate authority its light line and its deep-load line, because the location of these lines would affect the amount of tolls payable. Freight ships under the British flag have the plimsoll mark placed upon the hull, indicating the draft to which the rules of the British Board of Trade and Lloyd's Association permit the vessel to be loaded. Passenger ships which carry comparatively little cargo, and which usually have several decks above the main deck, always have much more freeboard than the minimum requirements of the law, and thus there is no occasion for them to have a Plimsoll mark or a load line upon their hulls. If, however, the maximum load displacement were made the basis of canal charges, it would be necessary for passenger ships to have their load line officially determined, although the action taken in locating this load line would have to follow rules largely artificial in character.

Quite as much difficulty would be encountered in establishing officially any vessel's light draft, for the reason that the vessel's light line locates the ship's draft when equipped for a voyage with fittings, crew, and supplies. Vessels have their light line established without fuel on board, but an increasing number of vessels now use oil instead of coal for fuel and the oil thus used is often carried in tanks which, in the case of coal-burning steamers, would probably be used for water ballast. An oil-burning steamer when light may have less water ballast than a coalburning steamer. The draft of a vessel without cargo or passengers would not be the same at all times or for all voyages. Thus the establishment of any vessel's light line would necessarily result from the application of arbitrary rules difficult to formulate and more difficult to apply. 2. If the actual displacement tonnage of a vessel at the time of its application for passage through the canal is made the basis of tolls, shipmasters may seek to lessen the vessel's draft temporarily by reducing the amount of water ballast to a minimum limit as the entrance to the canal is approached, in order that the vessel may thereby have less draft and be required to pay less tolls. When the vessel passes from the canal to the sea, the ballast tanks could