5. What difference would you expect to find in your present ship if turning at full speed (a) with steam steering engine in use, (b) with hand-wheels only available? Also what difference at 10 knots under these circumstances? 6. Show that the influence of the after deadwood of a ship is favourable to turning when the rudder is first put over, but unfavourable when on the circle. 7. Enumerate all the advantages you think a twin-screw ship possesses in comparison with a single-screw ship. 8. State for your present ship how an object ahead could be best avoided, either by (a) Turning with full helm, both screws ahead; (b) Turning with full helm and one screw astern; or (c) Reversing both engines. CHAPTER XXII. 1. What is effective horse-power? The Greyhound was towed at the rate of 845 feet per minute, and the horizontal strain on the tow-rope, including an estimate of the air resistance of masts and rigging, was 6200 lbs. the E.H.P. at that speed. Find Ans. 159 H.P. nearly. 2. Suppose we took a destroyer of 250 tons displacement and 27 knots speed as a model, and designed a vessel of 10,000 tons displacement of similar form. At what speed of this vessel could we compare her resistance with that of the model at 27 knots? (The ratio of length will be 2/1990o) Ans. 50 knots. 3. A vessel of 7000 tons requires 10,000 I.H.P. to drive her 20 knots, and the I.H.P. at that speed is varying at the fourth power of the speed. Find approximately the I.H.P. necessary to drive a similar vessel of 10,000 tons at a speed of 21 knots. Ans. 16,000 I. H.P. 4. Make out a table for your present ship, giving speeds and corresponding horse-power. Construct a curve of power on base of speed, as Fig. 205, and make out a table, as for Drake, in Chapter XXII., giving increments of power for every knot from 10 knots to the highest speed. 5. In the previous question, do any of the spots come manifestly below the general run of the curve? Are any of these due to (a) foulness of bottom, (b) bad weather, or (c) running in shallow water? 6. Enumerate the various factors which make up the difference between the E.H.P. and the I.H.P. of a ship. 7. Explain the reasons why it is of great importance to keep the bottoms of war-ships clean. How often is your present ship put into dry dock? 8. If it were possible to instal enough power to drive a submarine at high speed, would you not expect that the speed below water would be greater than the speed on the surface, in view of the absence of wave-making resistance? 9. Which is the more economically propelled at full speed, a duck or a fish? 10. Suppose one engine of Drake broke down, at what speed do you estimate she could go, (a) "with all despatch," (b) "with despatch," (c) "with moderate despatch?" Ans. (a) 18-19 knots; (b) 17-171 knots; (c) 141-15 knots. 11. A twin-screw Atlantic liner in mid Atlantic breaks one propeller shaft, and it is stated that she finishes the voyage with one engine at threequarter speed. How do you account for a falling-off of only a quarter the speed, with a reduction of one-half the power? CHAPTER XXIII. 1. Discuss in general terms the difference between the conditions under which a naval architect has to design and build a war-ship and an architect to design and build a large building, or a civil engineer a bridge. 2. Discuss in general terms the conditions under which a war-ship designer has to work as compared with a naval architect designing large steamers of the Mercantile Marine. 3. State the advantages of having a forecastle in a war-vessel designed for high speed. 4. What advantages from a gunnery point of view are found in a warship of high freeboard, in addition to the advantages of comfort and seaworthiness? 5. Make a comparison between the dimensions and particulars of H.M.S. Drake and Duncan of nearly the same displacement, and indicate as far as you can the reasons for the differences in each case. 6. State the reasons which have caused large Atlantic liners to be considerably larger than the largest cruisers. Automatic valves, 70 BACKING, teak, behind armour, 155 Battens for observing rolling, 233 Beams, construction of, 38 -, strength of, 1 --, support to, 41 Beck's automatic valve, 70 Bellerophon, protection of, 137 Bilge keels, action of, 225 Bracket frame, 24 Breadth of ship, definition of, 166 Bulkhead armour, construction of, 146 Bulkheads, numbering of, 64 watertight, 60 Bulwark class, protection of, 147 centre of, 180 reserve of, 177 Butt fastening for wood deck, 47 CALCULATIONS for area and volume, 159 Canopus class, protection of, 146 Capacity of pumps in a battle-ship, 97 Carlings, 40 Cast steel, tests of, 14 Caulking sheathing, 123 steel plates, etc., 19 wood decks, 48 Cement, 125 in bolt holes of sheathing, 123 Centre of buoyancy, 180 influence on stability, 187 of flotation, 204 of gravity, 180 Chambers, water, to diminish rolling, 227 Change of trim, 204 Circles, turning, 237 Clutches to steering gear, 94 Coal bunkers, ventilation of, 109 Coal stowage as affecting stability, 197 Coaling of ships, 127 Coefficient of fineness, 174 Cofferdam bulkhead, 60 Collision bulk head, 60 Corresponding speeds, 249 Corticine for decks, 48 Countersinking, 16 County class of cruisers, protection of, 151 Crank ship, steadiest in a seaway, 230 |