The subdivision of the hull into separate watertight compartments by means of plate iron bulkheads calls for particular notice. The following observations by Mr. Williams will show the importance of this improvement, and an effectual method of carrying it into practice.
"The casualties to which ships (especially steam vessels) are liable arise, for the most part, first from striking against or coming in forcible contact with rocks, or such solid bodies as would injure the frame-work of the vessel; and, secondly, from accidental collision with other vessels, by which some part of one, or both, becomes so damaged as to admit the water to such an extent as to overcome the power of the crew to pump it out.
"That any expedient shall be discovered which will prevent the irruption of the water to an extent beyond what may be within the power of men and pumps to expel, is hopeless. Even in the event of running on an anchor, or other body, which should break any part of the ship's bottom or side, or of a single plank starting, the extent of the injury would most likely be such as to render it impossible to keep the vessel afloat by human power. It occurred to me, that the only practicable expedient for preventing the sinking or actua submersion of the entire vessel would be by confining the effect of the injury sustained to that portion or section of the vessel in which the injury occurred; and this is the basis of the plan I am now to submit. The plan of dividing the vessel's hull into sections, each of which should be completely water-tight, has, we are told, been practised by the Chinese in their trade barges. This mode of giving security first occurred to me on building the iron steamer Garryowen (now plying on the Shannon at Limerick), and the trade barges which the Dublin Company's steamers tow on that river.
Where the hull was of iron, as in the Garryowen, the introduction of iron plate bulkheads was easy and effective; and, independently of the great strength afforded by this internal and sectional bridging (as it may be called), these sections were as susceptible of being made water-tight as the hull itself.
"Experience has proved that it is impossible to make a timber partition or bulkhead water-tight, or, at least, that it should continue so. The heat of the vessel is sufficient to cause such a shrinking in a partition of timber planking as to render it wholly useless in preventing water from passing. Iron plate partitions, however, possess all the requisites for this effectual division of the vessel into so many water-tight compartments. Their introduction, then, into timber vessels appeared an important desideratum. The only parts where water could find its way from any one section when filled to another section not so filled, would be, not through the iron partitions, but at the sides and bottom of the vessel, where they come in connexion with the frame and planking of the vessel. The preventing the water from passing in this direction is effected by very simple means, viz. by making this part of the vessel solid, that is, without those rooms or spaces which intervene between the frames of the vessel; this solid framing should extend 18 inches before and abaft each partition. The mode of effecting this is familiar to all shipbuilders.
The introduction of hair-felt between this solid framing and the planking on the outside and the ceiling on the inside completes the operation; the plate iron forming the partition having proper diagonal stays to give it strength, and being connected at the sides and bottom with angle iron, accurately fitted to the shape of the vessel, particularly in passing over the kelsons."
With regard to the number of these bulkheads, Mr. Williams is of opinion that four bulkheads, dividing the vessel into five compartments, afford the most eligible arrangement. The centre section will then be occupied by the engine, boiler, and coal bunkers. The section next to the centre will form the fore and after holds; or in the case of passenger vessels, the fore and after cabins; and the two remaining sections at the bow and stern need not be so high as the main deck, as the water never could rise within several feet of the same.
To prove the efficiency of these bulkheads, Mr. Williams tested the plan experimentally, under the inspection of the members of the British Association, in a new vessel, the Royal Adelaide. The vessel was first bored in the bow section, and the water allowed to flow freely in. When so filled that the water remained at the same height, outside and inside the section, it depressed the vessel at the bow six inches, and raised the stern about two inches. The water was then pumped out, and the adjoining section filled; this depressed the bow 12 inches without perceptibly raising the stern.