Navies of the world

by Edward W. Very

French Transport Annamite.
(Composite.)

The French system as applied in their light gun-boats has the same wooden outer skin, with the ordinary iron frame. The outer planking is double, gaining great longitudinal strength by breaking seams. There is no diagonal bracing. This system of outer planking is the one used in the English Navy. In the French transports of the Annamite class a system of alternate framing is followed, with wooden ceiling and double outside planking. In these vessels additional longitudinal strength is gained by the use of heavy iron box-stringers in place of the ordinary water-ways.

Iron Construction.

In tracing the development of iron construction it is necessary to pass from the consideration of unarmored vessels to the armored types, as the pure iron construction is limited almost exclusively to these vessels. The advantages of iron over wood may be summed up as being, 1st, lightness combined with strength; 2d, durability when properly treated; 3d, ease and cheapness of construction and repair; 4th, safety when properly constructed and subdivided. Its disadvantages are: (1) easy penetration of the bottom by rocks or by other pointed substances; (2) fouling of the bottom and consequent loss of speed; (3) the immense holes made, not only by taking out solid pieces, but, what is worse, the long rents or tears made by a penetrating shot through the thin side-plates and frames. Fast cruisers cannot be built of iron alone on account of the fouling, and the smaller the ship the greater the harm from this cause. War-vessels of any kind are excluded from this construction on account of the vulnerability of the sides, combined with the impossibility to stop a shot-hole which is starred with long rents. In the heavy iron-clad, however, the third disadvantage is done away with by the application of armor. The second is partially overcome by the surplus engine-power, and the first is neutralized by the double bottom, wing passages and compartments which the large roomy hull allows to be introduced.

The Brazilian iron-clad corvette Brazil, although built as late as 1866, is a good example of the primitive iron construction as applied to vessels of war. The keel of this vessel is what is known as the solid-bar type, the plates forming the garboard-strakes turning down on each side of it. The frames, made of upper and lower angle-irons strengthened from the amidship line to the turn of the bilge by a deep web, abut against an interior keel formed of a single plate surmounted by a flat plate-keelson, the frames, keels, and keelson being thoroughly bound together by angle-iron. The stem is scarfed into the keel, rising as a continuation of it and being rabbeted for the reception of the bow-plates. The main longitudinal strengthening consists in an iron bulkhead rising from the bilge to the under side of the main-deck and running fore and aft, forming water-tight wing passages. Just outside of the edges of the plate-keelson is what is called an intercostal longitudinal frame, consisting of short plates between the webs of the frames and secured to them by angle-irons; these frames run fore and aft. In addition to these longitudinal supports, a wide stringer-plate is carried along underneath the water-ways of both decks. In the formation of the armor-shelf, the exterior angle-irons of the frames, turned back along the edge of the web, form the shelf, while the interior angle-irons are carried up unbroken to the plank-sheer. The plating is the system generally applied of every other plate lapping on both edges.

Brazil.

Warrior.

In the Warrior the solid-bar keel gives way to the plate-keel, which in this case is double, the garboard-strakes butting against the edges of the internal plate, while the external one laps well over the joint. The continuous internal keel is found in this ship similar to the Brazil, secured by angle-irons to the inner keel-plate and the broad plate-keelson. The lower angle-irons in this case are continuous, while the upper ones are in short lengths, permitting the upper angle-irons of the frame to pass across and form a continuous length from plank-sheer to plank-sheer. The web of the frame is here shown increased in depth to a maximum, being lightened as far as possible by circular sections cut out. The assemblage of a frame consists of the continuous inner angle-irons, one on each side of a narrow strip to which the deep web-pieces are bolted, and the lower angle-irons bounding the webs. In the Warrior will be noticed six longitudinal frames similar to the continuous inner keel, and it will be noticed that the third of these frames, forming the seat of the wing-passage bulkhead, and the sixth, running along the outer edge of the floor-plates, project beyond the angle-irons of the transverse frame, being slotted to permit these angle-irons to pass them. The wing-passage bulkhead forms another longitudinal support, extending fore and aft from the turn of the bilge to the lower side of the main-deck. The armor shelf-plate in this instance consists simply of a broad plate bent at right angles and secured by angle-irons to the inner plating. This is a noticeable feature, as the extreme strain on the plate in the sharp bend is a plane of weakness.