are continuous over the entire length of the hold. Such a vessel may also be used to advantage for the shipment of coal, lumber, or other bulk cargoes.

A type of vessel known as "whaleback" is in some respects similar to a turret-deck vessel, but the number of whalebacks likely to use the Panama Canal is too small to warrant the reproduction of deck plans, cross sections, or longitudinal profiles. Both whaleback and turret vessels dispense with fore and aft sheer, both are designed for bulk cargo, and the gunwale

is of rounded form in each case. The whaleback steamer, however, differs from the turretdeck vessel in that it aims to provide absolutely clear decks without deck erections and with a rounded form which breaks the force of the sea. It was found that it is difficult for the crew to man such a deck in heavy seas, that the hatchways without coamings interfere with feeding the holds with bulk cargoes, and that the shape of the bow and bottom "makes the hull specially liable to damage when the vessel is pitching in a seaway, owing to the pounding action

FIG. 18. HOLD VIEW OF SELF-TRIMMING TURRET STEAMER.

ace, the cargo in

no danger that a shifting

ek cargo not injured by the samer and upon the mai There are other types of se eamers above mentioned. ams, pillars, or other hold obst ilk freight are applied to vi irret or trunk arrangement esel, which does not differ exten ater-baliset tanks between the

61861°-13.

(To face page 26.)

produced as the vessel thumps against head seas." 1 Relatively few whalebacks are in operation while the turret steamers, on the contrary, are rapidly increasing in number.

The trunk steamer is another special type of bulk carrier without a lower deck. Its general design is indicated by figure 19. There is above the upper deck a trunk erection which is 7 feet high and half the width of that deck. This trunk connects the forecastle with the bridge and the bridge with the poop. The hold is clear except for widely spaced pillars which extend from the floor of the hold to the angle formed by the upper deck beams and the frames of the sides of the trunk. One-half the pillar may be carried up the side of the trunk and be riveted to the plating. The upper deck beams do not extend across the ship; but strong crossbeams, in such number as the strength of the ship requires, are placed across the open portion of the upper deck. With the exception of the crossbeams the hold is clear below the hatchways which are in the trunk deck.

Turret and trunk steamers, being especially intended for dead-weight and bulk cargoes, have a relatively small freeboard below the harbor and upper decks, but the turret and trunk

decks from which the ships are navigated are well above the water line. When the hold and the trunk are filled with grain or other bulk cargo that may come, by settling, to occupy less space, the cargo in the turret or trunk feeds into the hold, which is kept filled, and thus there is no danger that a shifting of the cargo may give the vessel a dangerous list. Lumber or other deck cargo not injured by the sea is sometimes carried upon the harbor deck of the turret steamer and upon the main (or upper) deck of the trunk steamer.

There are other types of self-trimming steamers than the self-trimming turret and trunk steamers above mentioned. The principles of a clear hold without a lower deck, lower deck beams, pillars, or other hold obstructions, and with arrangements to facilitate the trimming of bulk freight are applied to vessels which have their walls carried to the upper deck without turret or trunk arrangement. Figure 20, for example, shows the hold view of a self-trimming vessel, which does not differ externally from any ordinary steamer. This particular vessel has water-ballast tanks between the self-trimming frames and the walls of the ship, which bring

1 Walton, Present-Day Shipbuilding, p. 69.

its water-ballast capacity to nearly a third of the total dead-weight carrying capacity of the ship. It is essential that measurement rules should deal fairly with those water-ballast spaces which are not available for cargo; while, in case of turret and trunk steamers, the rules should ully account for the inclosed turret and trunk deck spaces which constitute parts of the cargo capacity.

Tank steamers are largely used for the transportation in bulk of petroleum and of some other oils. The fluidity of oil in bulk and the danger of explosion from the gases formed of petroleum require a special construction of tank steamers to make them stable and safe. The part of the hold occupied by the oil in bulk is subdivided into small tanks; first, by a strong longitudinal bulkhead extending the entire length of the ship above the center line of the vessel and rising to the uppermost deck; second, by transverse bulkheads spaced about 24 feet apart. The small tanks thus formed being filled with oil when the vessel is loaded, the fore-and-aft and side-to-side movement of the oil due to the pitching and rolling of the vessel at sea is reduced to a minimum. To provide for the expansion of petroleum, due to increase in temperature, and to prevent explosion, due to forming of gases, an expansion trunk or space is placed 'tween decks. between each oil tank and the hatch opening into the tank.

The general plan of a typical large oil tank steamer is shown in figures 21, 22, and 23. The plans of the oil steamer illustrated by figures 21, 22, and 23 show that the tanks are placed amidships with the engines aft. There is a small cargo hold forward of the tank. Between the tanks and the cross bunker adjacent to the engine room are two water-tight bulkheads spaced a few feet from each other to provide a cofferdam between the tanks and the engine room. A similar cofferdam is placed between the cargo hold and the oil tanks. These cofferdams may be filled with water or kept empty, their purpose being to prevent the escape of gases from the oil tanks to the engine room or to the cargo hold. Coal or fuel oil for the engines may be carried in the reserve bunkers located between the expansion trunk and the outer shell of the ship. The vessel has four decks-a lower, which is dispensed with, a main, an upper, and a "shelter" deck. The "shelter" deck, however, is without tonnage openings and is a shelter deck only in name. The space between it and the upper deck, not occupied by expansion trunks, is available for fuel, freight, stores, crew quarters, and officers' accommodations. As indicated in figure 21, various superstructures, such as the galley, smoking room, chart room, and lamp room are located above the shelter deck. Some of the space between the main and upper deck is taken up by so-called "summer tanks," which are used for stowing oil during the warmer seasons. These summer tanks are constructed and tested as required for ordinary oil compartments and are likewise fitted with expansion trunks.

Figure 24 contains the deck plan and longitudinal profile of an oil tank vessel equipped with Diesel oil engines. This vessel has but three decks-a lower deck, which is dispensed with, an upper deck, and a shelter deck; and it has no summer tanks. Above the "shelter" deck is a long poop surrounding the light and air casing above the engine room. The space in the poop is used for living quarters.

The special feature of this vessel is the engine and fuel arrangement. There is no boiler room because Diesel engines are of the internal-combustion type. The engine room is larger than would be necessary to hold the engines, it being enlarged sufficiently to bring its volume somewhat over 13 per cent of the vessel's gross tonnage in order thereby to entitle it to a power deduction of 32 per cent of the gross tonnage under the measurement rules of Germany. The fuel oil is carried partly in fuel tanks and partly in double-bottom compartments below the engine The total fuel space is very much less in volume than it would be were the ship fitted with steam engines burning either oil or coal.

room.

Figure 25 illustrates a combination freight and passenger vessel fitted with Diesel engines. It is 370 feet long, of 53 feet beam, 9,800 tons displacement, and 7,400 tons cargo capacity. It is mainly a general cargo vessel, but has accommodations for 20 passengers, and has a speed of 11 to 12 knots. Aside from the engine-room arrangement, which is similar to that shown in the preceding figure, and the absence of boilers, this vessel illustrates various additional phases of ship construction and tonnage measurement. (1) The usual smoke funnels are dispensed