974
MODERN STEAM PRACTICE.
first, and then taking down, and fitting up in a foreign Station whereskilled labour is scarce, are saved, and also the freightage. Suchstructures can readily be fitted up entire in this country, andsteamed or tugged out to their destination. VVith this object in
view the writer has suggested the above form of navigable dock(Fig. 672). The hüll, it will be seen, is like an ordinary ship,having a pointed bow and stern. The middle chamber is formedaccordingly, and the top chamber is curved, and the ends filled inwith lattice work, having gates at the stern just like an ordinarydry dock, or the end of the dock may be filled up with a caisson;with this mode of construction more water ballast ■ can be left inthe basement when a vessel is being docked, as the dock can besunk to within a few feet of the top of the middle chamber. Thereis another advantage in the proposed form—the side surface isgreatly reduced, and the wind has not so much effect as on a wall-sided structure. With the view of making the dock complete it isproposed to place two screw propellers at the stern, having enginesof sufficient power to propel the dock at a moderate speed. Tur-bine wheels could likewise be adopted for that purpose, so arrangedthat the water is ejected from the basement when required. Largeand commodious workshops can be arranged in the top chambers,with punching, shearing, turning machines, &c.; in fact this typeof dock for foreign stations should be fitted up as a large floatingfactory. It is likewise proposed to utilize the middle chambersby placing guns of the heaviest calibre within them, with indentedembrasures suited for the end-on mode of attack; thus makingthe dock serviceable alike in time of peace or of war (see Fig.673). With the view of inspecting the outside plating at the