Decks, Bulkheads, and Flooding

Decks, Bulkheads and Flooding Decks- A horizontal platform extending across the hull at various heights above the inner bottom. Decks may have camber or sheer

Decks, Bulkheads, and Flooding Purpose of decks Upper deck Increases the vessel’s seaworthiness by forming a watertight top to the hull Contributes strength by acting as the upper flange to the hull girder

Decks, Bulkheads, and Flooding Purpose of decks Lower decks Working platforms for the operation of machinery and the loading of cargo Provide living spaces for passengers and crew

Decks, Bulkheads, and Flooding Purpose of decks Serve as horizontal diaphragm, keeping the ship in shape longitudinally

Decks, Bulkheads, and Flooding Deck Strength and Plating thickness Decks support the load of cargo, boarding seas, and stresses associated with the hull girder. Most hull girder stress will be concentrated amidships and outboard.

Decks, Bulkheads, and Flooding Deck Strength and Plating (cont’d) Due to the openings in the center line area (cargo hatch and machinery spaces) plating will be thicker at the continuous outboard deck plate. This plate is the Stringer Plate. Plating and under deck structure may also be heavier in the amidships region.

Decks, Bulkheads, and Flooding Stress Concentrations As mentioned in “Baker”, the S.S. Majestic suffered a near catastrophic failure of the strength deck. This failure was not due to insufficient deck plating thickness or under deck construction. Rather, it was caused by a concentration of stresses at the uptakes. The stress started a fracture which ran across the stringer plate, down the hull, and finally stopped at a port hole.

Decks, Bulkheads, and Flooding Stress Concentrations (cont’d) The fact that the fracture run stopped at a port hole is significant. The stress was dissipated by the circular nature of the port hole. All cuts in the main ship structure should be doubled and the corners well rounded.

Decks, Bulkheads, and Flooding Sheathing, covering, and insulating In older construction, decks were often sheathed with wood. This did little to add to the deck’s ability to withstand longitudinal stress, but did stiffen its resistance to heavy seas.

Decks, Bulkheads, and Flooding

Decks, Bulkheads, and Flooding Wood sheathing also: Insulates the space below due to the low heat transmission value of wood keeps the open decks from becoming so hot that passengers are unable to walk on them Prevent sweating due to rapid temperature changes underneath the deck Adds to the appearance of the vessel (Passenger Ships)

Decks, Bulkheads, and Flooding Insulation In more modern construction, decks are often insulated rather than sheathed. This may be accomplished with insulation bats fixed to the underside of the deck with metal wire studs or by spraying insulation directly to the steel deck.

Decks, Bulkheads, and Flooding

Decks, Bulkheads, and Flooding

Decks, Bulkheads, and Flooding

Decks, Bulkheads, and Flooding Insulation, in addition to insulating the space below and preventing sweating, can, depending on the construction and density of the material, act as a noise barrier. This is especially useful on engine room decks and bulkheads and on Passenger Vessels.

Decks, Bulkheads, and Flooding Deck coverings The steel that forms the deck plating will often be covered. In some cases, such as store rooms or work shops, it is just painted. For passenger and crew accommodations, galleys, passageways, wheelhouse, and other public areas, the steel deck is covered with a cement composite material which has a limited flexibility. This flexibility allows for the flexing of the deck plating is a seaway. The cement composite is then covered with tile, carpet, or linoleum.

Decks, Bulkheads, and Flooding

Decks, Bulkheads, and Flooding Bulkheads are important for the following reasons: If watertight, they prevent water from passing from one compartment to another, and in the case of a shell plating puncture, may save the ship

Decks, Bulkheads, and Flooding Bulkheads are important for the following reasons (cont’d): They act as fire checks by providing fire-resistant boundaries. After all other means have failed, they permit the flooding of a hold to extinguish a fire.

Decks, Bulkheads, and Flooding Bulkheads are important for the following reasons (cont’d): They act as structural diaphragms and resist the transverse deformation of the hull caused by racking stress.

Decks, Bulkheads, and Flooding Bulkheads may be constructed of flat plate steel or may be corrugated to add strength and reduce the need for additional framing.

Decks, Bulkheads, and Flooding

Decks, Bulkheads, and Flooding Bulkhead Spacing Vessels should be able to sustain a hull puncture and survive. Passenger Vessels, due to the nature of their cargo, should be relatively safer than pure cargo vessels.

Decks, Bulkheads, and Flooding Bulkhead Spacing (cont’d) There are voluminous rules enforced by the USCG, ABS, Load Line Regulations, and Senate Report 184 for the number and spacing of bulkheads on U.S. flag ships. Rather than have each flag state place restrictive regulations on only their vessels, an international convention was agreed upon. The result is the SOLAS (Safety Of Life At Sea) Convention.

Decks, Bulkheads, and Flooding Bulkhead Spacing (cont’d) The SOLAS convention of 1949 stabilized the bulkheads spacing issue and also addressed other safety areas such as lifeboats, life rafts, radio, watertight doors, etc.

Decks, Bulkheads, and Flooding Bulkhead Spacing (cont’d) It is possible to build vessels to be practically unsinkable. The navy builds ships with a great deal of compartmentalization. That way, if the hull is breached, the entire vessel will not flood. This construction technique is not economically feasibly in merchant ships.

Decks, Bulkheads, and Flooding Bulkhead Spacing (cont’d) A compromise was necessary to satisfy the crew welfare advocates, the insurance underwriters, and military usage experts who wanted close bulkhead spacing and the ship owners and cargo shippers who needed more open decks to handle cargo economically.

Decks, Bulkheads, and Flooding Bulkhead Spacing (cont’d) SOLAS 1949 graded ships as to their general character with cargo vessel that carry less than 12 passengers on one end of the scale and luxury liners that carry thousands of passengers on the other. This grading determined the number of compartments a vessel must have.

Decks, Bulkheads, and Flooding Bulkhead Spacing (cont’d) A one compartment ship is one that will stay afloat with one compartment flooded. A two compartment ship will stay afloat with two compartments flooded. Ex. A small cargo vessel (400 ft) that carries less than 12 passengers would be a one compartment ship where a large (800 ft) passenger ship with 1000 passengers would be a 3 compartment ship.

Decks, Bulkheads, and Flooding

Decks, Bulkheads, and Flooding Additional Regulatory Requirements for Bulkheads: Collision Bulkhead Should the vessel be in a collision and sustain damage to its bow, the collision bulkhead would act as an auxiliary, watertight bow. This bulkhead must be placed no more than 1/20 of the length of the vessel aft of the stem (measured at the load line).

Decks, Bulkheads, and Flooding Additional Regulatory Requirements for Bulkheads (cont’d): Afterpeak Bulkhead This bulkhead is required in all screw vessels. It must enclose the shaft into a watertight compartment. A watertight afterpeak bulkhead prevents a broken propeller shaft from flooding the entire aft section of the vessel.

Decks, Bulkheads, and Flooding Additional Regulatory Requirements for Bulkheads (cont’d): Machinery Space Bulkheads Machinery spaces must be enclosed by watertight bulkheads.

Decks, Bulkheads, and Flooding

Decks, Bulkheads, and Flooding Bulkhead Plating and Stiffeners Bulkheads are usually plated horizontally. Plate thickness increases gradually toward the bottom of the ship due to increased water pressure. As with plating, stiffeners increase in dimension and scantling toward the bottom of the ship.

Decks, Bulkheads, and Flooding Longitudinal Bulkheads Longitudinal bulkheads are avoided in normal freighter construction because of the danger of capsizing in the event of a collision. As with the S.S. Empress of Ireland, a collision in the E/R caused unequal flooding. The vessel capsized with a loss of over 1000 lives.

Decks, Bulkheads, and Flooding

Decks, Bulkheads, and Flooding Longitudinal Bulkheads Tankers are the exception to the longitudinal bulkhead rule. In most single hull construction, there are port and starboard longitudinal bulkheads. These bulkheads form the boundaries between the port, center, and starboard tanks. In double hull construction, there is usually only a center line longitudinal bulkhead.