Watertight Bulkhead

deck opening is situated aft, there must be at least two openings in all the transverse bulkheads in the 'tween deck on the fore side of it to entitle the space to exemption.

As will be explained later, the regulations governing vessel measurement in some countries other than Great Britain, particularly in the United States, define closed-in and open spaces more rigidly; and the 'tween deck space under the "shelter deck" is usually included in the shelter-deck vessel's tonnage by American admeasurers. The British Board of Trade and its admeasurers are compelled by an unfortunate decision of the House of Lords rendered in 1875 to treat as "open" the spaces under the shelter deck (and also under the bridge deck) that fulfill certain stipulations which prevent spaces from being considered as technically closed-in spaces, which American admeasurers treat as capable of being closed-in and as available for the stowage of dry cargo.

As actually constructed at present, there is but little difference between three-decked vessels classified as awning-deck and shelter-deck ships. In the awning-deck vessel, the 'tween deck spaces under the awning deck have only hatch openings which can be made weather proof; while vessels, constructed to meet the requirements of the British Board of Trade regulations as to shelter-deck openings, must have a tonnage hatch that can not be tightly battened down; it must have the bulkhead openings above described, and there must be scuppers and water ports to carry off the water that may reach the main deck. The ports, however, may have back valves to prevent the sea from washing in, and the tonnage hatch may be so constructed as to enable it to be so covered as temporarily to keep the sea water from invading the 'tween-deck space. In practice, British vessels which fulfill the Board of Trade requirements as to shelter-deck openings frequently carry dry cargo in the spaces under the shelter deck. When cargo is so carried, the British admeasurers add the space actually occupied by the cargo to the tonnage, upon which light dues and port charges are payable, but the 'tween-deck spaces are not added to the vessel's gross or net tonnage. In the United States and at the Suez Canal, on the contrary, the entire 'tween-deck space is included in the tonnage, if any dry cargo is or may be carried in the space.

The shelter deck is not necessarily the third or "upper" deck. It may be the fourth deck, as in the ship illustrated by the profile in figure 9. That vessel has an upper and a middle (or main) deck, the lower deck being dispensed with and compensated for by additional strength of framing. A ship built according to the profile shown in figure 9 exceeds the minimum requirements of the British rules as to open spaces, two tonnage openings being provided-one fore and one aft. If either one of these openings were kept permanently open and if the bulkheads between decks under the top deck were provided with permanent openings, there would be no question that all the space between the shelter and upper decks would be excluded from net tonnage by the British measurement rules; but, as a matter of fact, there is no reason other than that of keeping the vessel's net tonnage at a low figure why the bulkheads between decks should have nonclosable openings. In a vessel with four decks, nearly all of the space under the "shelter deck" would naturally be used for accommodating passengers or for stowing miscellaneous cargo.

The term "shelter deck" is sometimes applied to the fourth deck on large steamers (figs. 11, 12, 13, 14, 21, and 22), even though such deck has no tonnage openings whatever, but is a complete deck in every sense and is so regarded under the measurement rules of all nations. This terminology adds to the confusion concerning shelter decks, for such decks are so named merely for convenience. They are not shelter decks in the meaning of measurement rules and as the term is ordinarily used. A modern shelter-deck ship is one which has a full-length deck fitted with one or more tonnage openings, with scuppers and ports, and with bulkhead openings as provided in the measurement rules of Great Britain. The measurement or exemption of such shelter-deck spaces when fitted with tonnage openings, which are but technical openings, has been and is one of the main differences between the measurement rules of the several nations. Passenger vessels are sometimes fitted with a so-called "shade deck" or lightly constructed covering over the uppermost deck to afford a shelter and to provide a promenade for passengers. Ordinarily such a deck is constructed with light deck beams supported on round iron stanchions,