With the Britannic and Germanic as models of 5,000 tons and 5,000 horse power at 16 knot speed, the 24 knot vessel would require to be of 57,000 tons and 85,000 horse power, to carry sufficient coal for the voyage of 3,000 miles.  These enormous vessels being out of the question, the designer must reduce the size.  But now the City of Paris will no longer serve as a model, he must look elsewhere for a vessel of high speed, and smaller scale, and naturally he picks out a torpedo boat at the other end of the scale.  A speed of 24 knots—­and it is claimed even of 25, 26, and 27 knots—­has been attained on the mile by a torpedo boat.  But such a performance is useless for our mode of comparison, as sufficient fuel at this high speed for ten or twelve hours only at most can be carried—­a voyage of, say, 500 miles; while our steamer is required to carry coal for 3,000 miles.  The Russian torpedo boat Wiborg, for instance, is designed to carry coal for 1,200 miles at 10 knot speed; but at 20 knots this fuel would last only twenty-seven hours, carrying the vessel 540 miles.  It will now be found that with this limited coal capacity the speed of the ordinary torpedo boat must be reduced considerably below 10 knots for it to be able to cross the Atlantic, 3,000 miles under steam.  So that, even at a possible speed of 10 knots for the voyage, the full sized 24 knot five-day vessel, of which the best torpedo boat is the model, must have (2.4)^{6}, say 200 times the tonnage, and (2.4)^{7}, or 460 times the horse power.  The enlarged Wiborg would thus not differ much from the enlarged City of Paris.  A better model to select would be one of the recent dispatch boats, commerce destroyers, or torpedo catchers, recently designed by Mr. W.H.  White, for our navy—­the Intrepid or Endymion, for instance.  The Intrepid is 300 ft. by 44 ft., 3,600 tons, and 9,000 horse power for 20 knot speed, with 800 hours’ coal capacity for 8,000 miles at 10 knot speed; which will reduce to 3,000 miles at 16 knots, and 2,000 miles at 20 knots.

The Endymion is 360 ft. by 60 ft., with coal capacity for 2,800 miles at 18 knot speed, or for about 144 hours or six days.  The enlarged Endymion for the same voyage of 2,800 miles in five days, or at 211/2 knot speed, would be 44 per cent larger and broader, that is 520 ft. by 86 ft., and of threefold tonnage, and three and a half times, or about 30,000 horse power—­about the dimensions of the Furst Bismarck, but much more powerfully engined.  This agrees fairly with the estimate in the SCIENTIFIC AMERICAN of 19th Sept, 1891., where it is stated that twenty-two boilers, at a working pressure of 180 lb. on the square inch, would be required, allowing 11/2 lb. of coal per horse power hour.

The Intrepid, enlarged to a 24 knot boat, for the same length of voyage of 3,000 miles, would be 650 ft. by 100 ft., 40,000 tons, and about 45,000 horse power.  So now we are nearing the Messrs. Thomson design in the Naval Exhibition of the five-day steamer, 231/2 knot speed, 630 ft. by 73 ft., and 30,000 to 40,000 horse power.