Few naval officers are thoroughly familiar with the terms “gross” and “net” register tonnage unless their work has to do with merchant shipping. These two “tonnages”—of the four used in connection with vessels—are solely measures applied to commercial craft. Further, they are arbitrary measures of no value in the actual working of a ship. Although they have a general relationship to the size of the vessel, they do not express either the capacity of the holds or the amount of weight that the ship will lift. Neither one is a concrete and factual figure, such as displacement tonnage. In fact, gross and net tonnages are not measures of weight at all; they are volumetric units of one hundred cubic feet. As such they are wholly empirical yardsticks for purposes of taxation.
Upon one or the other of these two tonnages there will be levied, at some tariff rate per ton, the dues and charges for the use of harbors, canals, wharves, drydocks and similar facilities throughout the life of the ship and in all parts of the world. In twenty years of active life a ship will incur such charges many, many times. Obviously it is highly desirable that a vessel’s register tonnages shall be as small as is consonant with the service for which it is intended. Any qualified naval architect could accomplish this if the governing conditions permitted. Unfortunately, they do not.
As yardsticks for taxation purposes there is more than a little similarity between the rules for arriving at register tonnages and those for determining income tax. Each depends upon an intricate collection of laws, formulas, and interpretations, fully comprehensible only to an expert in the field. Such an expert can secure the least permissible tax base in either case for any given set of rules. But the ship is built for world-wide trading and the naval architect knows that there is no universally accepted system of tonnage measurement. There are, first, the national systems adopted by governments for their respective ships. These are generally similar but may differ in some important respects. Then there are the two canal systems, Suez and Panama, which differ radically from national systems and from each other. If the designer draws his plans to take the maximum advantage of one system of measurement, he is likely to find that he will be penalized under one of the other systems. From the economic standpoint world-wide uniformity of tonnage measurement would be highly desirable.
But, except for his over-all interest in the welfare of the American Merchant Marine, the naval officer has little direct concern with the economics of shipping: what should arouse his professional interest is the fact that all present systems of tonnage measurement tend, in some directions, to limit improvements in design, to “freeze” existing practices, and even to prejudice the safety or seaworthiness of the ship. It is this situation which furnishes the strongest argument for the long-overdue revision of tonnage rules.
To see how this condition came about it is necessary to go back into history because measurement rules, like so many maritime customs, have a long, intricate background and originated under conditions very different from those of today. Back in the 1400’s the principal import commodity of England was wine, upon which the king levied his “customs.” To make smuggling difficult Henry V decreed that wine would be imported only in casks or tuns of 252 gallons.1 When taxes were extended to the ship itself they were based upon the number of tuns it could carry. This made necessary a means of determining that figure when the ship was loaded with other commodities.
Initially this was arrived at by multiplying length of keel by beam by depth and dividing the product by 100. Subsequently, because of the difficulty of measuring the depth of hold of a loaded vessel, depth was assumed to be half the beam and the formula
became: tonnage = LXBXB/2/100
The divisor of 100 was later changed to 94 and this formula, known as “Builders Old Measurement Rule” was adopted by Parliament in 1720. But the difficulty of measuring length of keel of a vessel afloat led to a further modification. Length of keel was arbitrarily assumed to be extreme over-all length of the ship less three-fifths of the beam. In 1773 the formula thus became:
tonnage= (L-3B/5)XBXB/2/94
It will be noted that the taxable dimensions were those of length and beam, with no penalty on depth or draft. The natural result illustrated clearly how tonnage rules can affect seaworthiness. Ships became narrow, deep, and cranky. Serious losses could be attributed directly to this rule. Royal Commissions were appointed in 1821, 1833, and 1849 to study the matter and propose improvements. None of these Commissions produced a satisfactory answer.
It remained for George Moorsom, a naval architect and the secretary of the 1849 Commission, to suggest in 1853 the system of measurement which is known by his name. He proposed to measure the entire internal capacity of the ship, using Simpson’s Rules, and so arrive at a gross tonnage expressed in cubic feet. From the gross tonnage he further proposed to deduct certain non-paying spaces, such as sail locker, machinery space, and bunkers, to arrive at a measure of the space available for cargo. This space he called the net tonnage. In order to make the least possible change in the existing tonnages of ships he proposed to adjust his measured capacity by some constant so that the average net tonnage under the new rules would approximate that under the old. By experiment he found this constant to be 98.22 but for convenience he went to the round figure of 100, which is why gross and net “tons” are of 100 cubic feet.
It will be seen that, of the two tonnages, gross was generally a measure of total size of the vessel and therefore of the demand that it made upon the facility—harbor, dock or whatever—-while net tonnage initially at least bore a relation to its earning capacity or ability to pay. The Moorsom System was incorporated in the Merchant Shipping Act of 1854, and its theory was subsequently adopted, more or less intact, by all other maritime states and is still basically in effect. Only additions and amendments have been made from time to time by different countries and by the two canals to meet changed conditions.
It must be borne in mind how enormously different shipping conditions were in 1854. Then there were probably not one hundred steam vessels in the world, excluding inland craft, and the great majority were sidewheelers. They burned coal in low pressure boilers. They had only one ’tween deck and none of the intricate upper structures of today. Their bunkers were carried in boarded-off spaces to suit the needs of the voyage. Only a handful were of metal. All other ships of the time were wooden sailing ships. The construction complexities which later arose to make the 1854 rules a nightmare were nonexistent.
The character of the steam plants of a century ago and the variables in the bunker space were responsible for a treatment of the machinery spaces which still exists in United States and other national rules. Moorsom was fearful of a sailing ship with a small auxiliary steam engine as a “rule-beater.” He accordingly provided that, if the actual measurement of the machinery space fell between 13 and 20 per cent of the gross tonnage of the ship, a blanket deduction of 32 per cent of the gross should be allowed for machinery and bunkers in arriving at the net. Otherwise the deduction would be 175 per cent of the actual measurement of the machinery space itself.
It will be seen that, if the machinery space measures 14 per cent of the ship’s gross tonnage, the ship is allowed an automatic deduction in arriving at net tonnage equal to 32 per cent of the gross. But if its machinery space measures 12 per cent of the gross the deduction becomes only 20 per cent. By this arbitrary allowance a compact, modern machinery space—which can easily be less than 12 per cent of the gross—is disproportionately penalized in terms of net tonnage. In addition, the carriage of oil fuel in double bottoms, which are exempted from all measurement, makes the arbitrary bunker allowance rather ridiculous. The 13 per cent minimum works against progress in engineering while, on the other hand, bunker allowance is startlingly excessive today.
In 1875 the House of Lords handed down a decision in the case of the small coasting steamer Bear which had far-reaching effects on ship design. Under Moorsom’s rules all enclosed spaces were measured in the gross tonnage. The Lords ruled that a space was not enclosed unless it could be secured water tight against the seas. If an opening was left in a space and could not be closed securely then that space was exempted from all measurement. This gave rise to the “shelter-decker” with “tonnage openings.” In present practice if there is an opening in the upper deck of the width of the cargo hatches and four feet in length, and if this opening cannot be closed weather tight, all the space under the deck is exempted from both the gross and net tonnage. The same ruling applies to forecastles and poops if they cannot be securely closed with water tight doors. The effect therefore is to penalize the safe closure of a space by including the space in the ship’s tonnages.
Less material, although also bearing on the safety of the vessel, is the limitation on the amount of water ballast. Panama rules and those of the United States exempt all spaces which can be used solely for water ballast. Suez rules and those of most foreign nations limit the deduction of ballast tanks above the inner bottom to some empirical proportion of gross tonnage. Since, by definition, ballast tanks cannot be used for any other purpose there is no reason for this limitation which may penalize a vessel for having a ballast capacity essential to her sea-keeping qualities or even her safety.
Some of the defects of the Moorsom rules were early recognized, particularly the machinery space deduction.2 When the Suez Canal was opened in 1869 it fixed the deduction on a basis of 175 per cent of the actual measurement of the machinery spaces and further limited it to a proportion of the gross tonnage. In other ways Suez rules differ from Moorsom’s, but the effort to overcome obvious shortcomings only resulted in the creation of another set of highly involved rules of its own.
Our own national rules contain a radical difference from those of other nations in regard to the treatment of passenger ships. Under R.S. 4151 all passenger cabins and staterooms constructed above the first deck which is not a deck to the hull are exempted from inclusion in the gross and therefore, of course, from the net. Maritime countries ordinarily accept a ship’s tonnage certificate when assessing dues providing the tonnage was arrived at by a system approximating that in force in the country whose port the ship enters. Our passenger ships’ tonnage is arrived at on such a drastically different basis that usually each ship carries an appendix to its certificate showing the spaces exempted under this special United States rule and foreign charges are levied on what would be the foreign measurement. An amusing example occurred in connection with the old Leviathan.
As the German Valerland it measured by German rules 23,500 net and 49,000 gross. When it was reconditioned after World War I, Albert Lesker, the Chairman of the Shipping Board, determined that it should be the largest liner in the world (just as it became the fastest by running trials with the Gulf Stream) and so, by not taking advantage of all exemptions, it emerged with a net of 27,- 700 and a gross of 54,000. Later in private hands, her operators tired of paying port charges on the inflated figure and had her remeasured under American rules which produced a net of 15,800 and a gross of 45,000. Thus, without undergoing any major structural changes and wholly on the basis of different measurement systems, the ship had three widely varying sets of tonnages. However, the Southampton authorities took a dim view of the sudden drop in the net tonnage on which their port charges were based and quite properly insisted on payment on the basis of British measurement.
In 1913, when the Panama Canal was approaching completion, Dr. Emory Johnson devised a set of measurement rules for use by that canal which was intended to avoid many of the defects of the earlier systems. Although based on the Moorsom principles they abolished the exemptions for spaces with “tonnage openings”—the so-called shelter-decker—and imposed no limitations on water ballast. As the most modern set of rules they were probably, as first drawn up, the least objectionable of any rules based on the Moorsom system. In 1938, however, under pressure from American passenger lines, the Johnson rules were modified to include some of the exemptions of passenger superstructures contained in the United States rules. This change seriously weakened the erstwhile position of the Panama rules as being those most likely to gain general acceptance.
In addition to the specific defects in the various systems, which could be clearly pinpointed, a general objection to all systems had arisen out of their complexity and lack of clarity. These had grown as modern naval architecture got further and further away from the simple ships of a century before and required governments constantly to adjust their rules, or the application of their rules, to meet special cases not provided for. This, in turn, led to an increasing number of “interpretations” of rules by the various national measurement officials and these interpretations were often strongly protested by the shipowner affected. The end result was to make tonnage measurement almost an esoteric art, comprehensible only to its professional practitioners.
All naval architects and shipbuilders deplored the situation but no one could propose a means of improving it. The measurement experts clung to the belief that the Moorsom system could be made satisfactory by minor modifications to suit their respective pet theories, although these latter seemed to differ as widely as possible. The shipping industry felt that there was little gain in exchanging one set of technicalities for another, and that what was needed was a sweeping change in the whole approach.
The League of Nations struggled for years with the problem and in 1939 brought out a set of rules closely patterned on the British application of the Moorsom system, but the world crisis in 1939 relegated them to the background. In 1945, when the United States commenced its studies in preparation for a Safety at Sea Conference, it placed the subject of revised tonnage measurement on the agenda. Opposition developed from the Panama Canal authorities, who sincerely believed that their rules were the best that could be devised, and from American shipping interests who feared that any change would work to their disadvantage. Accordingly the matter was dropped by the United States as a subject to be handled by the Safety Conference.
In 1946 a conference was held in Oslo between certain North European nations and this conference expressed a guarded approval of the Panama Canal rules as originally written, although preferring the League of Nations’ suggestion. In 1947 the United States sent unofficial observers to another Oslo Conference, to explore the possibility of adopting the Panama rules generally. Because , of the 1938 changes these were not acceptable to the conference, which specifically adhered to the League of Nations’ system. Nevertheless the United States observers felt that this country was making a mistake in not participating more actively in international tonnage measurement conferences.
In 1948 a third conference was held at Oslo to which the United States sent accredited observers. The Department of State invited the shipping industry to nominate one of these observers and Mr. Howard C. Towle, a distinguished naval architect who had made an intensive study of measurement rules, was selected. As a result of this mission the feeling spread throughout shipping circles that it might be found possible to improve measurement rules without injurious results to American shipping. Similarly, the Panama Canal authorities took a more open-minded view of possible modification of their rules. These were two great forward steps toward the active participation of the United States in the entire problem.
In 1949 the United Nations, through its Economic and Social Council, invited its member nations to express themselves on the desirability of a general adoption of the so- called Oslo or League of Nations, rules. This request required definite action on the part of this country. Accordingly an interdepartmental working group was set up to draft a reply. This group included representatives of the American Bureau of Shipping, Association of American Ship Owners, Lake Carriers’ Association, National Federation of American Shipping, Shipbuilders Council of America, and Panama Canal, as well as of all interested government agencies.
As a result of this meeting the United States Government advised the Secretary General of the United Nations that it was in favor of uniform tonnage measurement rules provided they did not restrict freedom of design leading to increased seaworthiness and safety, but that the Oslo rules, in its opinion, did not meet this requirement. The United States further stated that, if an immediate proposal was required, it would suggest the Panama Rules, but that it would prefer to postpone action until it had had time to make an intensive study and submit definitive proposals.
The effect of this reply is two-fold. First, it shelves the Oslo rules for the time being, since no universal system can be adopted without the participation of the United States. Second it places squarely upon the United States, by its own action, the responsibility of putting forward an alternative and acceptable system within a reasonable time. Failure to do so would be stultifying. There the matter rests. A conference at Stockholm in June, 1950, discussed proposed interpretations and reached numerous conclusions, some of which would lead to greater uniformity of existing rules, but suggested few basic changes. The next conference will be held in 1952, at which time we should be able to make positive suggestions.
The basic principles that should govern an improved tonnage measurement system are simple. Obviously it must be internationally acceptable, in order to secure adoption. This will mean the continuance of gross and net tonnages, (several proposals have been advanced to have only one tonnage) and the new tonnages must approximate the old, in order that the thousands of tables of charges throughout the world will not be thrown into chaos. Even so, it is probable that existing ships will have to be given the option of accepting the new measurement or of retaining their old ones during the balance of their lives.
A new system must not penalize maximum safety. This would do away with the shelter- deck exemptions and the ballast tank limitations. It also should not operate against scientific or engineering progress, as does the machinery space deduction. The rules should be equitable, ship to ship, and should be clear and not subject to individual interpretation. So far as possible the tonnages should be calculable from the ships’ plans rather than require tedious actual measurement.
The solution of this problem is a challenge to the best efforts of all interested. It probably can only be found in some radical departure from previous practices. If a solution is reached it will lead to better, safer, and more efficient merchant vessels by freeing designers from some of the restraints presently imposed by tonnage rules. The Navy naturally has a substantial interest in such a result.
1. Thus is also established the “long” ton of 2,240 pounds.
2. By which many British tugs had negative net tonnage.