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Taking now the actual state of the ship with the turret ports, the battery doors, and the gun-ports open, the waterplane would be suddenly reduced to the shape shown by III in Fig. 208. This area only has a transverse moment of inertia of 2,783,000, lowering the transverse metacentre and bringing it below the C.G. This gave the ship a negative metacentric height of 18 ft., which rendered the ship unstable, and so she capsized.
The fore-and-aft distribution of the waterplane area, shown in Fig. 208, made a great reduction in the fore-and-aft moment of inertia of the waterplane, and this considerably decreased the "moment to change trim 1 in.," rendering the ship less and less able to resist change of trim as the water gained access to the forward compartments.
The following conclusions were reached as the result of the inquiry into the circumstances of the Victoria's loss:—
1. So far as can be judged, had all doors, hatchways, etc., been closed prior to the collision, the Victoria would have continued to retain ample buoyancy and stability, and would not have ceased to be under control.
2. Even when so seriously injured and brought to such a critical condition, as was the case, had the turret ports and upper deck battery been closed, the armour door secured, and water excluded from the turret and battery, the Victoria would not have capsized. It is possible that she may have eventually foundered in consequence of the gradual passage of water into the forward compartments.
3. That under the serious circumstances of this collision, or of any similar accident which may occur, the safety of a ship and her continued notation, demand that provision should be made for closing gun-ports and openings in upper works, through which water may pass into the interior of the ship, if the flooding of the compartments produces great change of trim or serious heeling.
If such precautions are not taken, the virtual height of freeboard is reduced to the height of sills or doors, and the presence of the superstructures, when water is not excluded from them, does not assist either buoyancy or stability to any sensible extent.
For a detailed account of the above, see—
(ii.) "Life of Admiral Tryon." Admiral Fitzgerald. (iii.) Brassey's Naval Annual, 1894. (iv.) Parliamentary Paper, No. C. 7208, of 1893.
1. Distinguish between the terms "structural" and "local" strains as applied to a ship. Enumerate a number of "local" strains. Have any of these local strains been sufficiently great in your experience to cause damage?
2. State the reasons for the superior efficiency of a I beam of steel to a solid rectangular beam of wood.
3. How may a ship be compared to a beam, and what parts of the structure are most efficient from this point of view?
4. How are the longitudinal strains on a ship's structure made the subject of calculation 1
5. Why is the structure at the keel and at the upper deck considerably stronger in a long cruiser than in a battle-ship of the same total displacement?
6. Why is it that the boat deck and the topside plating adjacent are not made an integral part of the structure in a ship having a boat deck?
7. To what special sort of strain are the flat portions of a ship forward specially liable? Why do you consider that this straining action is less in evidence in war-ships than in merchant steamers?
8. Why is it possible to build a steel or iron ship considerably lighter than a ship of the same size built of wood 1
9. Why must special attention be devoted to the strength of the upper deck and structure adjacent in a vessel of large proportion of length to depth? From this point of view, show that the most recent method of protection of large cruisers is more likely to prove economical as regards weight of hull structure than that adopted in, say, the cruisers of the Edgar class.
10. Suppose one had a vessel 300 ft. long, the structure of which had proved sufficiently strong, and a vessel of the same depth, but 360 ft. long were required. Discuss generally what portions of the structure would have to be strengthened to ensure the new vessel being sufficiently strong.
11. Indicate how the inspection and maintenance of a ship influences the design of the structure.
1. State the qualities of "mild steel" that make it a suitable material for shipbuilding purposes.
2. Compare in tabular form the tests laid down for " mild steel," "rivet steel," "cast steel."
3. What tests are necessary in a steel casting beside those relating to the strength and ductility of the material? Why are such tests of great importance for castings of steel?
4. Compare the tests for "mild steel" and those for the special steel used in cruisers and destroyers.
5. It iB laid down that holes in high-tensile steel must be drilled, and not punched. Why is this?
6. Describe the process of "pickling" steel plates. What trouble would you expect to arise in a ship's structure from the steel of which the "mill scale " had not been removed before painting?
7. Draw out to a large scale the section of a zed bar, a tee bulb, an angle bulb, and a I bar. State places in your present ship in which these sections are used.
8. A flange is frequently used on the edge of a plate instead of an angle bar for connection purposes. What advantage is thereby secured? State places in your present ship where this is done.
9. Describe the most ordinary form of rivet used in ship work, and show how such a rivet is used for the outer bottom plating where the outside surface must be flush.
10. What is meant by the pitch of rivets? State the amount of this pitch for rivets |-in. diameter where the work has to be watertight. What pitch would be used for 'j-in. rivets for internal work not watertight 1
Aixs. 4 to 41 in.; 5} to 6 in.
11. When your ship is next in dry dock, examine the "lap" caulking and the "butt" caulking of the outer bottom plating.
12. State the various advantages that result from ordering plating by the weight required per square foot rather than by thickness.
13. Taking the area of the outer bottom plating of a vessel as 30,000 square ft., estimate the saving of weight, if the steel plating is ordered 20 lbs. per square ft. instead of J in. thick. What further saving would be possible if the manufacturer sends in all the plating down to the limit allowed, viz. 5 per cent, under? Ans. 5-4tons; 13-4 tons.
14. If the area of the outer bottom plating (specified of 15 lbs.) is 20,000 square ft., what variation of weight is possible, in view of the latitude allowed to the manufacturer? Ans. About 13J tons.
15. What is annealing 1 What is the effect of annealing on a plate which has had a large number of holes punched in it?
1. Distinguish between "bracket frame" and "solid plate frame." Where are these frames used in a large armoured ship?