In one of the previous articles we have given some brief Introduction to the Load Lines and Conditions of the Load Line Assignment. As we all know, the assignment of the shipboard load lines and associated requirements are listed in the International Convention on Load Lines of 1969. Today, let us check what were the changes and developments that eventually led to the need for the subject governing document.
Need for a Standardized System
The need for a standardized international system of tonnage measurement of ships is evidenced by the fact that small ships of identical size and form may measure less than 200 gross tons or more than 1000 gross tons and the fact that exemptible and deductible spaces are treated differently under various national rules. The variations in tonnages cause inequities in the assessment of charges and in the application of provisions of treaties and laws.
This need for a standardized system was recognized in tin initiation of the League of Nations study and in the Oslo Convention. However, there were many differences in national systems and in those systems evolving from tin foregoing international activities that were yet to be resolved.
Work by the Intergovernmental Maritime Consultative Organization
In the meantime, the question of tonnage measurement had often been discussed by the Transport and Communications Commission of the United Nations. After the Intergovernmental Maritime Consultative Organization (IMCO) came into being in 1958, the task of developing a universal system of tonnage measurement of ships was taken over by the Organization as the United Nations had intended.
Against this background, IMCO formed a subcommittee of its Maritime Safety Committee in 1959 to study the problem and to draw up recommendations for a system of tonnage measurement suitable for worldwide application, which would be just and equitable between the individual ships and groups of ships, and would not hamper good design or mitigate seaworthiness, and which would take account of the economics of the shipping industry generally.
Over a period of years, the Subcommittee and its working group considered a number of proposals for a universal system of tonnage measurement. Finally the International Conference on Tonnage Measurement of Ships, 19G6, was held in London during a four-week period beginning May 27, 1969.
The Conference adopted the International Convention on Tonnage Measurement of Ships (ICTM, 1969), which the delegations felt largely met the above-listed criteria for a satisfactory system.
Tonnage measurement rules generally are spelled out in great detail in national laws. More detailed criteria for application of the laws are spelled out in regulations. The laws and regulations are interpreted by administrations established for the purpose. Since tonnages are used to determine the applicability of provisions of treaties, laws, and regulations and as bases for assessing charges, fees, and duties, any change in rules that would result in substantially different tonnage assignments for many vessels would disrupt the shipping industry. Historically, administrative decisions and rule changes have favored the ship owner, probably, because other segments of the shipping industry can protect their individual interests merely by changing rates for charges or by adopting parameters other than tonnages.
Transition from Deadweight to Volumetric Tonnage
The use of one half the breadth for the draft in the formula for approximating deadweight in the system preceding the Moorsom system led owners to acquire vessels that were poorly designed to obtain official tonnage assignments that were making the register tonnage a simple function of the volume of a vessel, the British opted for a coefficient (1/100) that would, on the average, slightly reduce the existing tonnages instead of opting for a coefficient that would more precisely approximate the deadweight.
The reasoning apparently was that if a system yielding higher, more precise deadweight tonnages were adopted, ship owners would find them burdened with higher bases for being assessed charges with no assurance that charging authorities would correspondingly reduce their rates. Other governments in amending their laws followed the example set by England. While the philosophy of avoiding radical changes in the tonnages assigned merchant vessels continues, governments can be persuaded to make their rules more logical.
In seeking a universal tonnage measurement system, the International Conference on Tonnage Measurement held in London in 1969 decided to do away with the system of exemptions and deductions from gross tonnage. The conference adopted a formula that would yield gross tonnages closely approximating those of vessels measured under present national rules without exemptions for shelter 'tween decks, deck spaces opened by tonnage openings, passenger spaces, and water-ballast spaces. On the other hand, the conference decided to maintain the net tonnage advantage enjoyed by shelter deck types and to extend that advantage to other types of vessels having low draft to depth ratios. That decision has already caused some charging authorities to shift their charge bases from net tonnage to gross tonnage.
Resistance to Illogical Changes
With varying degrees of success, governments have, at times, resisted illogical rule changes forced upon or willingly adopted by administrations of other governments. National rules usually provide that a space outside the double bottom adapted only to carry water ballast shall be included in the gross tonnage and deducted to arrive at net tonnage. They also provide that a space above deck shall be included in the gross tonnage if it is closed in and is available for the carriage of cargo or stores or for the berthing or accommodation of passengers or crew.
The United States adopted the Moorsom system by an Act of Congress dated May 6, 1864. That act specifically required passenger spaces to be included in the register tonnage. By an act dated February 28, 1865, however, the U.S. provided for the exemption of passenger spaces on or above the first deck which is not a deck to the hull. Only Liberia and Panama have followed that example. Pursuant to a law enacted February 6, 1909, until 1915 the U.S. included in the gross tonnage then deducted to arrive at net tonnage space adapted only for carrying water ballast out¬side the double bottom.
The most important area for load line improvement is that concerning the non-standard ship. Such ships might be treated casually by signatory nations but for two factors of great impact. The first factor is the legal realization that the International Load Line Convention, 1966 is the most widely applicable marine convention, since it requires a load line on every floating object with a horizontal dimension greater than 24 m unless it is a warship, fishing vessel or yacht. The second factor is the realization that the number and variety of ships which do not carry cargo in a weathertight interior have been increasing. Therefore, it is of some importance to outline these differences and explore those parts where new international agreement is needed most.
Let us examine those areas in which some of the new non-standard ships must be treated differently than the standard ship. First consider offshore drilling units. These can be subdivided into three general categories: Drillship, jack-up, and semi-submersible. The ship type fits the L/D, СB, and sheer of a standard ship but may not be fully maneuverable in a storm; therefore, sheer and bow height requirements are not utilized as contemplated by the Convention.
The jack-up type is a barge with limited stability while under tow and is also usually lacking in sheer and bow height. A semi-submersible has an L/D of no use in the strength evaluation, a very small СB so as to be transparent to waves, and no need for sheer nor bow height since normally the weather deck may be between 9 m and 30 m above the water whether under tow or drilling. Its loading capacity is often stability limited and it is essential for survival that no wave ever impact fully on the upper structure. While all of these types can be prepared for storms of various degrees of intensity, they are all dependent on advance weather warning for survival.
Surface-effect ships and hydrofoils need two separate evaluations as to their ability to weather a storm at sea. The first is in the waterborne mode and the second is in the out-of-water mode which involves high-speed interaction with waves and wind. In the latter mode, L/D, СB, sheer, etc., are essentially meaningless in the sense of the standard ship seakeeping evaluation assumed by Load Line Regulation.
High-speed planing hulls also defy the theory of sea-keeping in the sense of the standard ship, having a varying relation of Св and sheer to the seaway since their speed changes their displacement.
Catamarans and other multi-hull ships have no direct relation to Св, while ocean mining ships and pipe-laying barges are moored at a fixed heading allowing little opportunity to utilize bow height sheer effectively by turning into a storm sea.
Semi-submersible ships are now being built for several different services, some of which envision submerging at sea; this, incidentally, being prohibited by the Load Line Convention. Their purpose is primarily for the carriage of continental shelf equipment, heavy industrial items, and other barges.
If these ever engage in submerged operations while at sea, they must be designed to certain limits in obvious contradiction of the Load Line Convention and the government of registry must report the design limits to IMCO.
Thus far, the solution to finding a proper load line for these non-standard ships has been a separate evaluation of each design in the proposed maximum seaway conditions by the designer himself. Since a pure textbook solution to many of these problems is not feasible, it often means a series of intricate and expensive model tests to determine within generalized limits the adequacy of the design and geometric parameters for safety at sea.
In order to find the best approach to overall safety at sea for each of these non-standard ships and at the same time retain the value of the Load Line Convention as a legally acceptable certificate of evaluation for seaworthiness around the world, there is a need for further international agreements. This can be accomplished as a series of special codes or as additional annexes to the Convention; however, it remains to be seen if the many different types of non-standard ships can be successfully generalized.
Generalizing the large numbers of non-standard ships may be done in a variety of ways. Legally, in order to retain for all vessels the general safety foundation established for ship-shaped hulls by the Convention, it may be necessary to drop the definition of international voyage now used and to substitute a definition which includes operation on and exposure to the sea anywhere in the world as both standard and non-standard ships have a need for the governmental protection offered by the Load Line Convention.
As a function of design, they may be categorized by differences in form, geometry, stability, and seakeeping limits. Regarding service, they may be categorized by type of cargo, length of voyage or area of operation. Finally, it is evident to the authors of this chapter that non-standard ships will be proliferating and will most certainly be operationally limited by the Administrations until research and development has progressed to a point where administrations can predict the effect of seaway operation on these ships and will therefore permit wider latitude in their use
The freeboard can be limited in several ways, such as:
- The numerical calculation of ship's geometry;
- The structurally limited design draft;
- Stability limitations.
Another method of fixing draft, hence limiting freeboard, is by requiring a particular level of subdivision safety for the ship.
Although subdivision is not actually required by the In¬ternational Convention on Load Lines, the Convention does recognize subdivision as one of the several reasons for allowing tankers a reduced freeboard and permits other ships properly subdivided to approach tanker.
As a load line matter, subdivision is somewhat controversial from two points of view. The first is the fact that some national administrations require the subdivision calculation only at the load line draft. The second difficulty sometimes expressed is that the freeboard assigned to the ship is automatically spoken of as reserve buoyancy without an examination of the internal bulkheading in the ship. Since bulkheading is not actually required for load line purposes, there are ships which do not have adequate internal compartmentation to qualify for any degree of subdivision.
The bulkheading that exists in many ships provides an unknown level of subdivision safety which can only be assessed by calculation. When any loss of buoyancy occurs, the ship must depend for its survival on the volume of ship above the normal waterline, which is not a part of the flooded portion of the ship. Thus, part of the same volume that is used for reserve buoyancy of an intact ship in a seaway earlier in this chapter is now used for protection against sinking from loss of internal buoyancy. This could be termed residual buoyancy.
There is an important distinction between the two types of buoyancy. Reserve buoyancy for seakindliness and safety in a storm is considered fully intact at all times and the crew of the ship is responsible for properly maintaining all closures in order that this buoyancy remains effective against the sea. Residual buoyancy for resistance to flooding is, by definition, a matter of internal compartmentation of the hull.
The hull may lose some or all of its watertight integrity at any time due to stranding, collision, shell fracture, fire-fighting action, ruptured seawater piping, loss of hatch covers, etc. The rationale for subdivision is not to provide an unsinkable ship. The folly of that idea should have been permanently established with the loss of the Titanic, some seventy years ago. Instead, subdivision is used to provide a level of safety which enhances the probability of survival from flooding or prolongs the time for damage control action to be taken by the crew or by ship salvage crews and finally provides extra time for the people on board the ship to be safely removed if this becomes necessary.
For ships required to have load lines which also require a subdivision analysis, a check is made to ascertain that the permissible geometric load line draft does not exceed the subdivision draft.
Passenger Ship Subdivision Load Lines
The Inter¬national Convention for the Safety of Life at Sea requires that every ship carrying more than 12 passengers on an international voyage must be examined and must satisfy a particular level of subdivision. The level required for each ship is set by formula and is dependent upon the number of passengers which the ship intends to carry and the length of ship.
There are two ways to approach this subdivision draft. The first is via Fart В of Chapter II of the 1974 SOLAS Convention. The second is through the use of an alternative method explained and contained in IMCO Resolution A.260(VII). It utilizes the same basic parameters of persons, that is, passengers and crew, and length of ship. However, additional factors have been considered based on probable statistical occurrence of damage.
Factors from previous casualties such as damage position along the length of the ship, extent of damage, existence of longitudinal bulkheads, loading and permeabilities, sea states, and finally a corroboration of formulas by model test were all used to decide the final format and coefficients for the formula replacing the SOLAS 1974 method of determining compliance. The advantages of the new method are principally that established shipbuilding techniques, such as longitudinal bulkheading, which were not creditable under SOLAS 1974 are now officially recognized in the formulas as a subdivision asset. Also, greater latitude in internal bulkhead arrangements can be accounted for.
In addition to the international rules for subdivision, which apply to all passengers ships making international voyages. United States regulations require subdivision calculations for all passenger ships on the navigable waters of the United States, whether on foreign, coastwise or Great Lakes voyages, or for ferryboats on inland waters.
After the application of all the corrections to the basic Minimum Summer Freeboard are made, the result is the Minimum Summer Freeboard in salt water which will be assigned to the vessel. This freeboard may in no case be less than 50 mm. For ships having hatchways with covers other than steel or equivalent material on the freeboard deck or on superstructure decks situated forward of a point located a quarter of the ship's length from the forward perpendicular, the freeboard is not less than 150 mm.
Load Line Format
The freeboard is measured from the top of the deck amidships to the top of the line through the center of the load-line ring. Forward of the ring is a grid composed of lines indicating the maximum loadings in fresh water and for the different seasons, including the summer line which will be at the same level as the center of the ring.
Zones and Seasons
The regulations require a vessel to be so loaded when departing upon a voyage that at no time during any portion of the voyage will the applicable seasonal mark be submerged. The oceans of the world are divided under the regulations into various zones and seasonal areas according to the probable severity of the weather. In certain areas and times of the year where during the winter more severe weather may be expected the vessel is required not to load as deeply as is permitted in the summer.
These areas are the seasonal winter zones, and the times of the year when the winter mark is applicable are shown on a map attached to the regulations. During other times of the year, the summer mark at the center of the ring is applicable. Other zones, roughly corresponding to the temperate zone in the northern and southern hemispheres, are permanent summer zones under the regulations where the summer mark is applicable the year around.
Another zone, on either side of the equator, is a permanent tropical zone where the anticipated weather is generally less severe than might be expected in the summer in the temperate zone. In these zones vessels are permitted to load somewhat deeper any time during the year. Other areas between the permanent summer and tropical zones arc considered one or the other at specified different times of the year.
Calculation of Seasonal Marks
The various seasonal and fresh water marks are obtained as follows:
Tropical Freeboard Mark (T)
The line to mark the maximum loading in the tropical zone is obtained as a deduction from the Summer Freeboard of one forty-eighth of the summer draft measured from the top of the keel to the center of the ring. Again, the freeboard must not be less than 50 mm or 150 mm.
Winter Freeboard Mark (W)
The line to mark the maximum loading in winter zones is obtained by an addition to the Summer Freeboard of one forty-eighth of the molded summer draft.
Winter North Atlantic Freeboard (WNA)
The minimum freeboard for ships of not more than 100 m in length which enter any part of the North Atlantic defined in the regulations during the winter seasonal period shall be the winter freeboard plus 50 mm. For other ships, the Winter North Atlantic Freeboard shall be the winter freeboard.
Fresh-Water (F and TF)
The regulations apply to vessels at sea in salt water. An allowance is computed as a guide in compensating for deeper draft when a vessel loads in fresh water. The fresh water allowance in cm is determined by dividing the displacement at the summer load waterline by forty times the tons per cm immersion at the draft. The fresh-water allowance in inches is determined by dividing the summer load line displacement by forty times the tons per inch immersion at that draft.
If the basic information is not available, the allowance is taken at one forty-eighth of the summer draft. The fresh-water allowance applies to all seasonal freeboards, but fresh-water lines arc marked on the vessel only for the summer and tropical conditions. Where the water is brackish, a proportion of the fresh-water allowance is used, and a measurement of the actual density of the water at the place of loading may be required.
In addition to the fresh-water allowance, deeper loading is also permitted to allow for consumables used between the point of loading and the open sea.
If a Timber Freeboard is assigned it is marked in addition to the ordinary load lines with some slight variation. The Winter Timber Freeboard is obtained by adding to the Summer Timber Freeboard one thirty-sixth of the molded summer timber draft. The Winter North Atlantic Timber Freeboard is not to be less than the ordinary Winter North Atlantic Free¬board.
It is of vital importance that there be provided efficient means of protection for all openings to the hull and superstructures, for the protection of the crew in heavy weather and for the rapid freeing of water from the weather decks. The regulations to ensure compliance with these considerations are grouped together as Conditions of Assignment.
By the terms of the International Load Line Convention (ICLL, 1966), freeboard may not be officially assigned until the ship has been inspected and a qualified surveyor representing the Administration of the flag country is willing to certify that the Conditions of Assignment have been met.
These Conditions of Assignment must not only be complied with initially but they must be at all times maintained in satisfactory condition. Their vital importance is recognized in the regulations which call for annual inspections to be made by the assigning authorities' Surveyors to ensure that, in fact, they have been maintained in satisfactory condition for the continued validity of the Load Line Certificate.
In the Convention (ICLL, 1966) repeated in the Regula¬tions (46CFR42), are the specific formulas for minimum height of openings, strength, deflection, etc. for each of the items covered by the following subsections. They are described here in general form so that one realizes that a significant portion of load line review and freeboard assignment is dependent upon the watertight integrity of the hull, and the weathertight integrity of the ship's topside area.
Most important, because of their size, are the cargo hatchways. Standards are set forth in the regulations for the construction, heights of coamings, the covers, and the fittings of all exposed hatchways on the freeboard and superstructure decks. Hatchways inside superstructures must meet standards which depend upon the type of closing appliances fitted on the access openings in the end bulkheads.
The requirements for hatch coaming heights and hatchway covers, and their supports, comprise a standard of strength and protection. Coamings may be reduced in height, or eliminated altogether, in association with gasketed metal covers, subject to the approval of the flag administration. While the regulations specify strength criteria, the rules of most of the classification societies contain formulas for hatchcover and beam design which provide equivalent strength.
Machinery space openings on the exposed portions of the freeboard deck or superstructure decks, or within open structures, must be provided with steel casings, with any opening fitted with steel weathertight doors. Openings in required machinery casings must have specified minimum sill heights. Machinery access hatch openings are to have permanently attached steel weather-tight covers. Exposed machinery casings of Type A ships cannot have direct access from the freeboard deck to the machinery space.
Other Openings in Deck and Shell
Other openings include ventilators, air pipes, hull piping, and air ports.
Ventilators on exposed positions on the freeboard and superstructure decks leading to spaces below the freeboard deck, or to enclosed superstructures, are to be fitted with coamings of minimum height, depending upon the location, and with provision for temporary means of closing.
Air pipes from ballast tanks or other tanks below the freeboard deck, which extend above the freeboard deck or superstructure deck, are to be provided with a permanently attached means of closing.
In the sides of the vessel, the numerous small openings required present a problem in maintaining the intactness of the vessel. Each overboard discharge pipe leading from spaces below the freeboard deck must have an automatic non-return valve with positive means for closing from an accessible position above the freeboard deck, or in some instances, two automatic non-return valves without positive means of closing may be allowed if the inboard valve is always accessible in service. Scuppers or sanitary discharges from superstructures or deckhouses may also be required to have similar protection.
Portholes in superstructures on the freeboard deck or in the hull are required to be fitted with hinged deadlights. Any other openings in the shell below the freeboard deck such as gangway or cargo ports must have closures designed to ensure watertightness and structural integrity.
Miscellaneous Conditions of Assignment
Guard rails or bulwarks, gangways, lifelines, or other means must be provided for the protection of the crew in its operation of the vessel and for getting to and from their quarters. Deckhouses used for the accommodation of the crew are to be of adequate strength. Where bulwarks on the weather portions of freeboard or superstructure decks form wells, ample provision is made for freeing the decks rapidly of water and for draining the wells. The draining area re¬quirement is based on the length and height of the bulwark. In ships with no sheer or in those fitted with trunks restricting free flow of water across the deck, adjustments are made by increasing the freeing port area requirements to a degree.
Information to be Supplied to the Master
The master is to be furnished with sufficient information in an approved form satisfactory to the administration of registry. This is to enable the master to arrange for the loading and ballasting of his ship in such a way as to avoid the creation of any unacceptable stresses in the ship's structure. In some cases, based on the length, design, or class of ship, the administration may consider this requirement unnecessary. In addition, the master is to be supplied with sufficient information in an approved form to give him guidance as to the stability of the ship under varying conditions of service.
Timber Deck Cargos
Timber deck cargo refers to a cargo of timber carried on an uncovered part of a freeboard or superstructure deck. Such cargo may be regarded as providing the ship with certain additional buoyancy and a greater degree of protection against the sea. For that reason, ships carrying a timber deck cargo may be granted a reduction of freeboard calculated basically in accordance with the requirements for Type В ships with additional conditions stipulated relating to construction, stowage of the timber cargo, stability, protection of crew, and access to machinery and other such spaces necessary for the safe operation of the ship.
In the previous article we have touched the very basics of the shipboard load line. In order to assign a load line properly, it is necessary to compare the design to a geometric ship of the Standard form. The concept of the Standard Ship with definite geometric proportions was evolved early in the discussions for standard freeboard.
Board of Trade Standard Ship
From a historical standpoint, the 1906 Board of Trade Rules (Board of Trade, 1906) in England used a Required Reserve Buoyancy to establish desired winter freeboard for both steamers and sailing vessels. This Reserve Buoyancy referred only to the intact weathertight ship and was deemed necessary for safe seakeeping. The freeboard to be assigned was such that the percentage of the total volume of the hull above the load line was equal to that required in the table.
The required buoyancy was least for the shortest vessel, 20.4 percent at 22 m, and increased to 35.8 percent becoming maxi¬mum at a length of 183 m. The required extra buoyancy for sailing vessels was 1 percent to 2 percent higher than for steamers. However, in lieu of making a complete volumetric calculation up to the freeboard deck, the designer was permitted to use certain tables of winter freeboard provided by the Board of Trade based upon a standard length to depth ratio (L/D) of 12.
Freeboard reductions of a very small order were allowed for summer weather. On the other hand, an arbitrary addition of 50 mm in winter time for the Mid North Atlantic area was required.
In addition to the regular reserve buoyancy due to the basic freeboard amidships, the regulations also prescribed a standard sheer curve adding buoyancy at the bow and stern. This buoyancy was considered effective in promoting the seakeeping properties of ships in heavy weather.
The freeboard for a given length and depth also varied slightly according to the "coefficient of fineness" which was defined (Board of Trade, 1906) as the ratio of all under freeboard deck volume to the product of L x R x D.
ICLL 1930 Standard Ship
The Standard Ship of the 1930 Convention had:
• a L/D ratio equal to 15;
• a fineness coefficient equal to 0.68;
• a table of freeboards increasing with length of ship;
• a standard sheer; • a standard camber of the main deck;
• a minimum percentage length of superstructure;
• a required forecastle for tankers.
In the International Convention on Load Lines 1930, the coefficient of fineness was specially defined only in English units as follows:
where d1 figure was the mean molded draft at 85 percent of the molded depth. Subsequently, in the ICLL, 1966 the title Coefficient of Fineness was dropped and the correction is now called the Block Coefficient correction.
ICLL 1966 Standard Ship
The Standard Ship of the 1966 Convention (ICLL, 1966) is similar to the 1930 standard ship except for the camber requirement which was dropped and the forecastle requirement which was removed in favor of a minimum bow height for all manned vessels. The fineness coefficient was redefined as the block coefficient, as previously mentioned.
Some types of ships less than 100 m in length are expected to have a weathertight superstructure on at least 36 percent of their length which will add buoyancy and form a righting moment to resist extreme rolling. These ship types with superstructures covering less than 35 percent of the length must accept added freeboard.
The "Load Line" is actually a formally accepted term which has been given to a mark normally located amidships on both sides of a vessel in order to show the limiting draft, i.e. the one to which the ship is allowed to be loaded. The limiting value shall be obtained through measuring from the freeboard deck, usually the uppermost continuous weathertight deck of the ship, down to the load line mark. Subject distance is referred to as the ship's Freeboard. The load line mark itself is one of the essential requirements of the ICLL, 1996, standing for the International Convention on Load Lines 1966; in addition, same is required by the Public Law 93-115, 1973 in the United States.
The arrangement of this mark will be governed by the regulations that are issued by the government of the Flag's country, for example the USCG in America. The ICLL, 1966 requires the Administration of each country accepting this convention to provide all facets of load line examination and control. Since it involves continuous knowledge of the ship throughout its life, countries with no inspection staff often delegate portions or possibly all load line activities to classification societies.
Since the load line regulations apply to almost all ships and embody a complete review of the general seaworthiness of the vessel, it is therefore important that the designer consider not just the desired freeboard but all facets of safety governed by load line regulations early in the preliminary design. The associated calculations, legal assignment, and marking of the minimum allowable freeboard plus the overall seaworthiness evaluation are intended to make sure that the ship:
• has adequate structural integrity for the intended voyages;
• has adequate hull stability for the intended service;
• has a hull confirmed to be watertight from keel and up to the freeboard deck and weathertight above this deck;
• has a working platform located high enough from sea surface, thus allowing for the safe movement on the exposed deck in heavy seas;
• has adequate hull volume and reserve buoyancy, above the waterline - this guarantees that the ship will not be in danger of foundering/plunging when in a very heavy seaway.
The above five basic rules have been the guiding principles for many decisions made during the past century by classification societies and national administrations relative to the proper minimum freeboard for ships of all kinds. The history of official load lines is well documented by the discussions and papers noted in Board of Trade (1906), Norton (1942), and Ryan (1967) for the further guidance of those who wish to review the development of load lines.
The rules for determining the correct freeboard on any particular vessel are not scientifically exact. The freeboards determined under the international rules for vessels on international voyages evolved within the last 100 years. They are completely empirical and were initially based upon experience on vessels up to 91 m in length projected to 137 m in length. After the initial freeboards were set down as national legal requirements in Europe in 1890 they were amended from time to time and the tables extended gradually to lengths up to 229 m in 1915 when vessels still were generally well below that length.
Internationally, there have been only two load line conventions. The first was hosted by the UK back in 1930 and the second one was held in 1966 under the auspices of the UN agency for marine safety, which is the Inter-Governmental Maritime Consultative Organization (IMCO) located in London.
The five basic rules of load line philosophy mentioned earlier are embodied in an agreed set of regulations published in the International Convention on Load Lines (ICLL, 1966) currently in force. In America, the load lines were originally established by Congress in 1929 for foreign voyages and in 1935 for coastwise and Great Lakes voyages (Public Law, 74-354, 1935). Currently, the ICLL, 1966 is implemented by Public Law 93-115 dated October 1, 1973 which is reproduced in the United States Code 46 USC 86. Subject regulations implementing this law are detailed in the Code of Federal Regulations (46 CFR 42) which constitutes an almost verbatim copy of the technical Annex of the International Convention. All new ships 24 m or more in length which make an international voyage are required to be assigned load lines under this law. Warships, fishing vessels, existing vessels not exceeding 150 gross tons and pleasure yachts are exempted.