History of Gross and Net Tonnage Measurements
Gross and net tonnage are terms applied to vessels and not to commodities. One hundred cubic feet of space is a vessel ton, and the gross tonnage of a vessel is the number of tons of 100 cubic feet within the ship's closed-in spaces.
The cubical contents of the closed-in spaces within any particular vessel would seem to be a fixed quantity definitely determinable, and would supposedly be the same whatever the flag of the ship or in whatever country the vessel is registered; but the several national rules for the measurement of vessels define closed-in spaces differently, and these rules vary as to what spaces shall be exempted from measurement, and thus from gross tonnage.
Moreover, the Suez Canal Co.'s measurement rules are different from nearly all the national rules.
Origination of the Present Rules and Methods
The present rules or methods followed in measuring vessels to determine their gross tonnage originated with Mr. George Moorsom, of England, and were first embodied in law in the British tonnage act of 1854.
The Moorsom rules for the measurement of vessels have since then been adopted by practically all countries of the world and are now everywhere followed, although, as will presently be pointed out, the practice of the several nations of the world as to the exemption and measurement of spaces within vessels is far from uniform.
Prior to 1854 vessels were measured by brief rules which produced only approximately correct results. Those in force in England were established by the "new measurement" law of 1836.
The need for improvement in the rules having become evident, the commissioners of the admiralty, at the request of the Board of Trade, appointed a committee in 1849 to recommend changes in the rules.
The following year this committee recommended that the contents of vessels should no longer be determined by internal, but by external, measurement. Mr. Moorsom was honorary secretary of this commission, but did not approve of its recommendation.
Formulation of the Moorsom Measurement Rules
When it became evident that the report of 1850 was not to be accepted, Mr. Moorsom formulated the measurement rules which now bear his name. These rules were approved by the Board of Trade and made law by act of Parliament.
Mr. Moorsom worked out an exact mathematical method or formula for determining the cubical contents of vessels, and the ships then registered under the British flag were measured by these rules. It was found that the cubical contents of the entire British merchant marine was 363,412,456 cubic feet.
At that time the total registered tonnage of the fleet was 3,700,000. The ratio of the number of cubic feet of contents to the number of tons register was 98.22 to 1.
It was the desire of the British Government to make as little change as possible in the registered tonnage, and it was accordingly suggested by Mr. Moorsom that in order to simplify calculations 100 cubic feet instead of 98.22 should be considered a gross ton. Tnis suggestion was adopted.
Mr. Moorsom's recommendations regarding measurement rules and tonnage were embodied in Rules 1, 2, and 3 of the tonnage act of 1854. These rules, as now in force, are printed in full in Appendix III to this volume.
Rule 1 prescribes a method for measuring empty vessels, Rule 2 states how laden vessels shall be measured, and Rule 3 prescribes the rules to be followed in measuring the space occupied by the engine and machinery of steamships.
In their present form the rules differ only in minor respects from those originally formulated by Mr. Moorsom.
The first country to follow England in the adoption of the Moorsom system of measuring spaces and the Moorsom ton was the United States, which embodied them without change in the act of 1864.
The Suez Canal Co.'s measurement rules were formulated by the International Tonnage Commission which met at Constantinople in 1873. These rules provided that the gross tonnage of vessels shall be determined by the Moorsom system and be expressed in Moorsom tons.
Thus, by the action of the International Tonnage Commission and by the laws of the United States and other countries, a vessel ton is everywhere 100 cubic feet, and the contents of vessels are determined by the Moorsom system of measurement.
Spaces Included in Measurement of Gross Tonnage
The rules, however, concerning the spaces that shall be included in gross tonnage vary with different countries, and the regulations of the Suez Canal Co. are different from nearly all the national rules.
Dissimilarity in the several measurement codes is due to the fact that some include spaces which are exempted by other rules. Thus the same ship would not have the same measured contents and would not have the same gross tonnage by British, American, and Suez rules.
It is obvious that if gross tonnage were made the basis of Panama tolls it would not be possible to accept the gross register tonnage of vessels as stated in their national registry certificates, because ships of the same size having different gross register tonnage would not be treated "on terms of entire equality, so that there shall be no discrimination * * * in respect of the conditions or charges of traffic."
The Hay-Pauncefote treaty would be violated if Panama tolls were collected in accordance with the gross tonnage of vessels as stated in the ship's papers.
"Exemption" and "Deduction"
In discussing the measurement of vessels to determine their gross and net tonnage it is necessary to keep in mind the distinction between "exemption" and "deduction" from measurement.
Measurement rules stipulate what spaces shall be measured to determine a vessel's gross tonnage and what part of the vessel shall be exempted from measurement, while the rules governing the determination of net tonnage specify which of the spaces that have been measured shall be deducted.
Net tonnage, as will be explained later in detail, is ascertained by deducting from the contents of the spaces that have been measured and included in gross tonnage the contents of such spaces as the rules designate shall not be included within the net tonnage of the vessel.
The gross tonnage of a vessel depends upon the spaces exempted from and upon the spaces included within the measurement, while a ship's net tonnage is affected by the specifications of the rules as to the exemption of spaces from measurement and as to the deductions to be made from the spaces included within the gross tonnage.
The rules regarding the measurement and exemption of vessels control the gross tonnage and indirectly determine the net tonnage of vessels.
Johnson, Emory Richard, Measurement of Vessels for the Panama Canal, Volume 2, Government Printing Office, Washington, DC 1913, Pages 45-46