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Dead-Weight Tonnage

A vessel's dead-weight tonnage is the difference between the weight or displacement of the vessel when "light" and when loaded to its maximum authorized draft. It is the number of tons avoirdupois that the ship can carry of fuel, cargo, and passengers; it is the vessel's dead-weight capability, its carrying power.

The term dead-weight is also applied in commercial practice, to some extent, to the weight of coal and cargo actually aboard a ship at a given time. In this sense the dead-weight tonnage of a ship at any particular draft is the difference between its displacement "light" and its displacement at its actual draft.

Would it be wise to levy tolls either upon a ship's maximum dead-weight tonnage or upon the dead-weight of the fuel and lading actually aboard a vessel at the time of application for passage through the canal?

As an argument in favor of tolls upon maximum dead-weight tonnage, it is urged that charges based upon the ship's carrying power are placed upon the weight from which the owners of the ship may derive traffic revenues.

This argument is strengthened by the fact that the rates charged for the Use of chartered vessels—i. e., charter rates—are upon dead-weight tonnage and that, inasmuch as a large share of ocean freight is transported in chartered vessels, the commercial world is accustomed to charges based upon dead-weight tonnage.

Advantages of Dead-Weight Tonnage for Tolls

The advantages to be derived from making maximum dead-weight tonnage the basis of canal tolls are, however, more than offset by the objections to making that tonnage the unit of canal charges:

  1. Freight ships, especially those employed in the transportation of bulk cargoes, would be heavily taxed, because of their large carrying power, while passenger steamers having comparatively little dead-weight capability would be but lightly burdened with canal tolls. Unless the rates of toll were different for different types of ships, there would be relative injustice as among different classes of vessels.
  2. Even as between freight ships carrying different kinds of cargo the charges would be inequitable. The tolls payable would be largest for vessels loaded with the heaviest, and thus ordinarily the cheapest, commodities. Minerals, nitrate, lumber, grain, and other bulk commodities have large weight in comparison with value, and the canal tolls would fall most heavily upon the classes of commodities that ought to be most favored by the tolls.

If cargo were made the basis of tolls, articles which are shipped as package freight ought to be charged tolls not upon their weight but upon their measurement tonnage—40 cubic feet, instead of 2,240 pounds, being considered a ton.

This would probably not be practicable, but unless it were done the discrimination against heavy bulk cargoes would be unjust to the shippers of "dead weight freight." Carriers, moreover, would find tolls upon weight of cargo less desirable than charges upon space occupied by freight.

Would it be advisable to base Panama Canal tolls upon the actual weight carried by vessels using the canal? It would seem offhand that tolls upon the actual weight borne by the vessel would be on a proper and desirable basis. Ocean carriers would thus be called upon, to pay charges for the use of the canal varying with the amounts transported through the waterway.

The tolls would not be placed upon the vessel, but upon what is in the ship, and would be made to vary with the weight of the vessel's burden. Moreover, the tonnage upon which tolls were payable could theoretically be obtained without difficulty.

It would be necessary only to read off from the vessel's displacement or dead-weight scale the difference between the ship's "light" displacement and its actual displacement at the time of passing through the canal.

As a matter of fact, however, the objections to tolls based upon the actual weight carried by vessels are stronger than the merits of such a system of charges.

There are the same practical and equitable reasons against making actual dead-weight carried the basis of canal charges as there are against the maximum dead-weight tonnage as a basis for tolls.

There would be the same difficulty encountered in deciding what should be considered the "light" draft of a vessel and thus what should be taken to be its "light" displacement.

Likewise there would be the same inequity of charges as among different types of ships and as between similar ships carrying different kinds of cargo.

Johnson, Emory Richard, Measurement of Vessels for the Panama Canal, Volume 2, Government Printing Office, Washington, DC 1913, Pages 39-40

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