Page images

with oceangoing tramp ships engaged in the coal trades. There is, of course, danger of fire, and this is discussed elsewhere in the present volume.

The tramp ship that carries coal from the United Kingdom or the United States to South America or on other long deep-sea hauls is usually of the general service type, with engines amidship and with no special modifications of design incorporated specifically to fit the vessel for the carriage of coal. It is true that a 'tween-deck steamer is less suitable than a single-deck vessel for carrying coal, but there is not much limitation on size or draft, on the question of cubic capacity, or whether the ship should be a shelter-deck ship or a singledeck ship.

In the United States, United Kingdom, and Australian coastwise trades, and in the short-haul trades between the United Kingdom and Scandinavian, French Atlantic, and other ports there are many specially designed colliers which possess certain unique features of design and equipment to fit them for their highly specialized trade. Many of these ships must ordinarily make their return voyages in ballast, and for this reason they are fitted with extra large fore and aft peak tanks and double-bottom tanks. Extra ballasting arrangements are provided in a number of these ships by the installation of so-called topside ballast tanks. These are triangular compartments built in between the underside of the main deck and the ship's sides. These tanks, the construction of which contributes materially to the transverse strength of the ship, do not occupy much potential cargocarrying space, since coal, when loaded by gravity, stows in heaps that are somewhat pyramidal. Furthermore, when coal is loaded into a ship in such quantity as to put it down to its load line, the space occupied by the coal, on the average, will be only about fiveeighths of the total cargo space. In single-deck ships or in ships having a single tier of 'tween decks, the topside ballast tanks bind the hull structure together transversely to such an extent that, ordinarily, no hold pillars are required. This provides clear, unobstructed holds that greatly facilitate loading and unloading, thus helping to reduce the vessel's time in port.

Another method that is used in this type of ship to provide clear, pillarless holds is the use of the arch principle of construction. In this type of construction the top parts of the ship's frames are bent inward. The top part of the ship's midsection thus forms a transverse arch, which tends, as in the case of the topside ballast tank system, to bind the hull transversely. This construction also permits the depth of hold to be materially increased.

A great number of coastwise and short-sea colliers have their engines placed aft to provide an uninterrupted cargo space and eliminate the occupation of cargo space by the shaft tunnel. Many other such vessels, however, have their engines amidship and in a number of these the loss of space because of the shaft tunnel is offset by raising the aft deck to the same level as the bridge deck amidship. This type of ship-the raised quarter-deck type-has already been mentioned. Such ships were first designed and built on the northeast coast of England, the shipping point for the coal mines of the Tyne region.

Hatches on colliers are made as large as possible, consistent with the limits of structural safety. On short-sea colliers, the breadth of

the hatches is commonly from 65 percent to, in some cases, 75 percent of the molded breadth of the vessel. Especially wide hatches are desirable in these ships since they regularly load at tips and are unloaded by grabs, and the speed of loading and unloading is materially increased when wide hatches are available.

With colliers of this class, the loading is practically always the same, and there is little opportunity for the ship's officers to make any alterations in the disposition of the cargo which will have a marked effect on the stability. In this instance, the proportions of the ship weigh more heavily than in the case of the general cargo carrier. Modern vessels of this type are built with broader beams and lesser depth than was customary in the early years of the century, and the stability has been greatly improved by these alterations in design.


A paper by L. C. Burrill contains much valuable information on this subject, and for that reason excerpts stating some of the author's chief conclusions are quoted herewith.

From the point of view of general seaworthiness and sea-kindliness, the author places the various types of colliers in the following order: Three-island type; well-deck type (raised quarter-deck with engines amidship); arch colliers; raised quarter-deck type with engines aft.

Three-island type.-The three-island type, with single continuous deck fore and aft, is the most seaworthy, although not very much superior to raised quarterdeck ships with engines amidships. In these ships the forecastle minimizes the amount of water shipped forward, the raised poop serves as a protection against following seas, and the midship houses divide the ship in such a way that any water shipped is usually confined to either the after or forward well. Well-deck type (raised quarter-deck, engines amidships).-The disadvantage possessed by this type is that the forward well is likely to carry more water than the three-island type, owing to the decreased local freeboard. If a raised poop is not fitted they are also more likely to "dip" their sterns. A very good feature in these ships is the practice of raising the double bottom in the after hold to tunnel height, thus giving good ballast capacity and good ballast trim. Arch colliers.-These ships, having inverse sheer, possess more freeboard at amidships than other types, and in moderate weather are less wet and roll easily, but with heavy head seas they carry large quantities of water on the fore-deck, since the water must run forward to free the deck and frequently meets the next oncoming wave.

Raised quarter-deck type with engines aft.-This type of ship, being designed to present a long stretch of hatches to loading appliances, also presents a large open space to oncoming seas, and it is possible for heavy seas shipped forward to travel the full length of the ship, flooding the alleyways and striking each hatch in turn Owing to the heavy weights aft, these ships trim well by the stern in ballast condition, less ballast capacity being necessary to immerse the propellor. For this reason they are difficult to handle in bad weather, and roll heavily in this condition.


[ocr errors]


Vessels built for regular employment in the Scandinavian and other European lumber- or timber-carrying trades are generally given a broad beam in relation to draft in order to compensate for the high center of gravity caused by the carriage of large deck loads. A high center of gravity, such as is found in vessels carrying a deck

Burrill, L. C. Seaworthiness of Collier Types. A paper read before the British Institution of Naval Architects. March 1931.

load of lumber, tends to make the ship unstable and this tendency is counteracted to a considerable degree by providing a broader than usual beam. Many ships of this class are given a pronounced sheer forward to prevent the seas from sweeping along the deck and tearing loose the deck load. To accommodate a large underdeck load, vessels built for these trades generally have holds that are as free as possible of obstructions such as hold pillars and web frames.

Large ballast tanks without watertight subdivisions are likely to be a source of danger in ships that spend a large proportion of their time in the timber-carrying trade. A vessel with such tanks must either keep them full to prevent the water moving from side to side and possibly capsizing the ship, or must keep them empty, in which event the stability of the vessel may be impaired when carrying a deck load. If the tanks are full, the ship's carrying capacity is likely to be reduced. Because of these facts, modern ships designed for the European timber trades have their principal water ballast tanks carefully subdivided-an additional expense at the time of building, but one which is well worth while with regard to service.

Another point that must be taken into consideration in connection with these ships is that they are subject to severe wringing strains when rolling in a heavy sea which strikes them at an angle. The deck weight of the load in the after part of the ship, which has a natural tendency to continue its roll when a sea striking the bow has checked it forward, often causes a motion which results in cracked plates and brackets just forward of the engine room in ships which have not been specially strengthened at this point. Many timber-carrying ships are consequently strengthened at the vulnerable points at the time of building.

444742-42- -8



Stowage is generally understood to mean the placing and securing of cargo in the hold of a vessel, although the term "stowage" is also used in a broader sense to describe the complete operation of transferring cargo from the pier or other place of loading to the hold. It is truly an art and can be learned by the stevedore, the steamship company executive, or the ship's officer only through long experience in the handling of many types of commodities and shipping containers.


The principal objectives which those responsible for the stowage of cargo must aim to carry out are (1) stowage to protect the ship and crew from damage or injury; (2) stowage to protect the cargo from damage, tainting, or other injury; (3) stowage to make the best use of the cargo space so the vessel will carry the maximum load of weight and measurement cargo and obtain the maximum possible freight revenue; (4) the handling of the stowage operation with the maximum possible speed in order to save time and reduce stevedoring costs by keeping overtime to a minimum; and (5) stowage arranged so that cargo for different ports can be promptly and readily unloaded upon arrival.

Stowage for safety to the ship, the crew, and the cargo, and stowage to make the best use of the ship's capacity by careful distribution of weight and measurement cargo are discussed in detail in separate chapters of this volume. The achievement of maximum port speed and the conduct of the stowage operations to place cargo for different ports so that it can be unloaded without delay upon arrival are also considered in the chapter entitled "Receipt and Handling of Cargo at the Ocean Terminal." All these subjects are also of necessity touched on in the present chapter which deals with the general problems confronting the ship's officers, stevedores, or others in charge of stowing a ship's cargo, and with the specific methods of stowage which have been found suitable for commodities packed in the more commonly used types of shipping containers.


The stowage of a well-designed modern ocean-going vessel provided with good-sized hatch openings and relatively clear holds is in many respects a simpler matter than was the stowage of earlier vessels the hatches of which were narrow and the holds were obstructed by numerous stanchions, hold pillars, web frames, and other parts of the ship's structure.

There are still, however, almost innumerable problems to be dealt with in the stowage of any ship, despite the more efficient construction of the modern vessel. Stowage nowadays is frequently complicated, for example, by the fact that many vessels load cargo at a number of ports such as those of the North Atlantic range or the United States west coast-for discharge at a number of foreign ports. Obviously, this makes it more difficult to place all the cargo so that it will be immediately available when the port of discharge is reached. Take, as an example, a ship loading at New York, Philadelphia, Newport News, and Savannah, for Brisbane, Sydney, Melbourne, and Adelaide. Normally the cargo for Adelaide, the last port of call, would be placed in or near the bottom of the ship. However, if there is considerable Adelaide cargo to be loaded at Savannah, it may perforce have to be placed on top of cargo previously taken aboard for Brisbane, Sydney, and Melbourne. The difficulty cannot be solved by reserving a special hold for the Adelaide cargo, because it would take too long to discharge it through one hatch and because the weight in this hold might strain the vessel after the cargo for previous ports had been discharged.


A general rule that should be followed, unless circumstances absolutely prevent it, is to stow the cargo so that there is a fair or even distribution for each port over the different holds of the ship. For example, if there are 500 tons of cargo for a certain port to be loaded into a vessel having five holds, approximately 100 tons should be placed in each hold; not 20 tons in one hold, 250 tons in another, and so on. This not only helps in some measure to make the cargo for the various ports accessible at the proper time-since the cargo for the last port of discharge is placed in or near the bottom and the cargo for the first port of discharge on or near the top-but it also helps to speed up the discharge of cargo at each port, since all hatches can be worked at the same time. Even distribution is essential for quick dispatch.

Exception may properly be taken to the above rule when it is known that cargo will have to be loaded as well as discharged at the foreign port in question. Thus, if it is known that 100 or more tons of cargo will have to be taken on board at a certain port, the outward cargo for that port might be distributed evenly among three or four holds, leaving one or two holds (or 'tween-deck spaces) into which cargo can be loaded at the same time that the outward cargo is being discharged.

It should always be borne in mind that good stowage, in connection with cargo to be discharged at more than one port requires that when the cargo for the first port has been unloaded, the cargo for the remaining ports will still be well and safely secured for the ensuing sea passage. At the same time, the vessel must be kept in trim, and free from strains caused by unequal distribution of weights. This again emphasizes the necessity for distributing the cargo for the various ports more or less evenly between the different holds and 'tween-deck spaces of the ship.

Another difficulty that frequently arises to make stowage more difficult is the fact that goods are sometimes shipped as "optional

« PreviousContinue »