I Keel; Side bar keel 2 Garboard; Garboard strake. 3 Center girder; Vertical center plate; 5 Wing girder; Margin plate. 6 Floors; Intercostal floors. 7 Brackets. 8 Inner bottom; Top of double bottom; Top of tank. 9 Bracket frames.' 10 Web frames. Il Side stringers. 12 Diamond plates 13 Hold pillars, Hold stanchions. 14 Main deck beams. 15 Main deck stringer. 16 Main deck plating. 17 Main deck sheerstrake. 18 Topside strake 19 Upper deck sheerstrake. 20 Upper deck pillars; Upper deck stanchions. 21 Upper deck beams. 22 Upper deck. 23 Bulwark stay. 24 Bulwark plating. 25 Main rail; Roughtree rail. Keelson tudinal wing girder at the upward bend of the frames, are crossed at right angles by the longitudinal side girders that parallel the keelson. The floors may be continuous from keelson to margin plate and the side girders intercostal between the floors; or, as in figure 3, the longitudinal girders may be continuous and the floors may be intercostal between the girders. FIGURE 2.-Midship section of two-deck vessel. The second deck dispensed with, the vessel being given compensating strength by web frames and side stringers. Figure 3 is the drawing of a half cross-section of a three-deck vessel. The lower deck is omitted, and compensating strength is given the hull by introducing web frames for each fifth frame and by stiffening the hull by means of heavy longitudinal side stringers placed Web Frame 18 FIG. 4. MIDSHIP SECTION OF A STEAMER WITH THREE DECKS AND A intercostally between the web frames. The web frames extend only to the main deck; and it will be noted that there is a main-deck beam for each frame and that the main-deck floor is of steel plates. The upper deck construction is lighter; there are beams only for each alternate frame and the deck flooring is of wood. Instead of using web frames to strengthen the hull of vessels from which the lower deck is omitted, it is now more usual to employ "deep framing," i. e., to use deeper frames all of the same size. Figure 4 is a midship half section of a vessel with three decks besides a shelter deck. The lower deck is dispensed with to permit cargo to be stored in the hold and handled in and out more advantageously. The strength of hull sacrificed by leaving out the lower deck beams and floor is compensated for by web framing and by side stringers. The significance of the term "shelter deck" is explained below in discussing three and four decked vessels. The early ocean steamers and some of the small freight vessels now in service were constructed with two full decks, the lower and main decks, above which were placed the three usual superstructures the forecastle, bridge, and poop. The outline sketch, figure 5, indicates the general design of the two-deck vessel. In a two-deck ship the main deck may, as in figure 5, extend without a break from stem to stern; but the more usual practice is to raise the deck 4 or 5 feet from abaft the bridge to the stern, as is shown in figure 6, the raised portion of the main deck being called the quarterdeck. In a two-deck general cargo steamer it is usual to place the engine amidships, and the main purpose of the quarter-deck is to increase the capacity of the after cargo hold, which, on account of the space occupied by the shaft tunnel connecting the engine room with the propeller, and on account of the finer lines of the aft part of the hull as compared with the fore body of the ship, has less volume than the forward cargo hold. A vessel with a forward hold larger than the aft hold would tend to trim to the bow when loaded with homogeneous cargo. The quarter-deck enables the vessel to be loaded to an even keel. The forecastle and bridge being inclosed against the sea add to the buoyancy of the vessel, and with the early development of the ocean freight steamers the bridge was extended and brought nearer to the forecastle. In heavy weather the deck between the forecastle and bridge being awash, the space was appropriately called the well and the steamer with a well was called a well-deck ship. To increase the freeboard and reduce the shipping of water, the main deck forward of the bridge is sometimes raised 4 or 5 feet to form a raised fore deck. Such vessels are called "raised fore deckers." These types of ships are still used to some extent in the charter freight service. Figure 6 indicates the general arrangement of a raised quarter-deck, well-deck steamer. If the vessel were a raised fore decker the well would be shallower. The more detailed profile (fig. 7) of a well-deck steamer, without a quarter-deck, shows the location of the main parts of the ship. The lower deck is dispensed with and the hull is given compensating strength by deep framing and, in the engine and boiler rooms, by substituting "web frames" or beams for some of the frames. The vessel has a double bottom containing water ballast tanks. As is customary, the narrow parts of the ship at the bow and stern contain peak tanks that are generally used to carry water ballast. The bridge, as is usual, is built around the casings inclosing the smoke funnel and the ventilating spaces above the engine and boilers. The poop and forecastle are closed in and used for crew quarters and freight stowage. The profile also shows such other parts of steamers as the anchor-chain locker, bulkheads, hatches, deck house, and shaft tunnel, engine funnel, donkey engine and boiler recess, water-ballast tanks, steering-gear house and deck houses, all of which are spaces considered in measurement, and must be provided for in any code of measurement rules. They are indicated in figure 7 in case of a simple two-deck "well"-deck steamer, in order that the repeated use of these terms in succeeding chapters dealing with measurement rules may not be confusing. The typical ocean steamer of to-day is a three or four decked vessel, i. e., a vessel with three or four full-length decks. Until recently the three-deck vessel was the standard, and it might be a full scantling or "three-deck" vessel, a spar deck, an awning deck, or a shelter-deck vessel. In a "three-deck" vessel the frames are carried full sized to the upper deck, which is the strength deck of the ship. When the frames are made somewhat lighter between the middle and upper deck and the upper deck is of lighter construction, the vessel is a spar-deck ship; and if the construction above the middle deck is still lighter, and the middle deck is the strength deck, the vessel is called an awning-deck ship. The space between the awning and middle decks is closed against the sea and used to carry light cargo, cattle, or passengers. If there are one or more permanent openings left in the upper deck, so that in heavy weather the sea may invade the space between the upper and middle decks, the upper deck is called a shelter deck—not an awning deck-and the ship is named a shelter-deck vessel. The "three-deck" ship being stronger than a spar-deck vessel, is allowed the smallest freeboard, while the spar-deck ship is allowed less freeboard than is permitted an awning-deck vessel. For carrying heavy cargoes in rough seas the "three-deck" ship is preferable, while for transporting light commodities and package freight and passengers the awning-deck ship is preferable. The desirable strength and weight of a vessel are determined by the service it has to perform. The use of the term "shelter deck" in shipping literature and in measurement rules is confusing. Originally the shelter deck was one erected above the main deck or the upper deck to shelter cattle or other cargo that did not need to be carried in spaces from which the sea was completely excluded at all times. The shelter deck had permanent openings, while the awning deck was capable of being completely or "permanently closed in." With the evolution of ships, however, the shelter-deck vessel has come to differ very little from the awning-deck ship, as is clearly shown by figure 8, which is a profile of a steamer having lower, main, and shelter decks. The profile of the steamer illustrated by figure 8 shows that the shelter deck has closable hatches above all the hatches in the main and lower decks, but that there is a small tonnage opening in the shelter deck abaft the after hatch, placed there to meet the requirement of the British Board of Trade measurement rules. In order that this ship may be classified as a shelter-deck vessel by the Board of Trade, the tonnage opening must be not less than 4 feet long fore and aft and be at least as wide as the width of the after-cargo hatch on the same deck. The after edge of the tonnage opening must be distant from the aft side of the sternpost by not less than one-twentieth the registered length of the vessel. If the tonnage opening is placed forward, the fore side of it must be not less than one-fifth of the length of the vessel from the stem. Through the bulkheads that subdivide the space between the shelter and main decks there must be "permanent openings" at least 3 feet wide and 4 feet high; and, if coamings are fitted thereto, their height must not exceed 2 feet. When the permanent |