Watertight Bulkheads.—In regard to the general arrangement and method of stiffening a watertight bulkhead, bulkheads are assembled on some convenient flat surface and the rivet holes marked in the plating and stiffeners, after which they are trans ferred piece by piece and erected in their proper positions in the ship.
Erection.—The system and order of erection of the vessel varies in different districts, but the following general description may be considered as typical. After the keel blocks have been erected and faired, the flat plate keel is placed in position and the centre girder erected. The floors in the double bottom are then erected and the tank margin plate, the inner bottom plating and the outer bottom plating are attached to the floors. The side frames are then hoisted into position, and the deck beams, deck plating and side shell plating erected. The various parts of the i ships are temporarily secured by bolts, great care in the mean time being taken to see that the correct form of the vessel is maintained.
As each part of the work is completed by the platers it is ready for the riveters and caulkers, and these trades follow on without delay. Platers usually work in squads composed of three or f our platers, a marker boy and a number of labourers or helpers, the number depending on the size or weight of the plates and also on the facilities of the yard for handling such material.
On the work of a large vessel many such squads may be employed. The riveters also work in squads, a squad consisting of two riveters, a holder-on (whose duty it is to hold a large hammer against the head of the rivet while the point is being hammered down on the opposite side of the plate by the riveters), and a heater boy. Hand riveting is being largely supplanted by riveting executed by pneumatic hammers, while for those parts which can be riveted before being erected in position hydraulic riveting is employed. After the riveting is completed all watertight work is caulked, this process consisting of forming a shallow ridge along the edge of the plate to force this edge into close contact with the surface of the adjacent plate. A very important part of a caulker's work is testing the various watertight double bottom compartments or oil bunkers by filling them with water. A pres
sure is applied by means of a stand pipe carried to an appreciable height above the surface of the tank.
When the work on the hull is completed, the vessel is ready to be launched after being painted. It is usual to defer painting as long as possible so that the black mill scale on the plating may be exposed to the atmosphere and thus more readily removed. Red and white lead, oxide of iron and oxide of zinc form the basis of most of the paints used on steel ships.
In the early stages of the industry the oil was transported in barrels or in special tanks fitted in the holds, but this system was found to be very uneconomical and vessels were accordingly designed to carry the oil in bulk, the first ship of this kind being the "Gluckauf," built in i886.
The design of oil-carrying ships has passed through various phases, but for a considerable number of years past the great majority have been constructed on the longitudinal system of framing, more generally known as the Isherwood system. The oil is carried in tanks which form the structure of the ship, the boundaries of the tanks being formed by the skin of the ship, by transverse bulkheads spaced about 3o feet apart and by a middle line fore and aft bulkhead, which extends from the keel plate to the top deck. The second deck extends inwards from the ship's side for about one-quarter the breadth of the vessel and is united to the upper deck by a continuous longitudinal bulk head, the space between this bulkhead and the middle line bulk head being known as the expansion trunk, which permits of the expansion of the oil due to variations in temperature and also restricts the amount of movement of the oil when the ship rolls.