Page:Popular Science Monthly Volume 22.djvu/226

214 great extent counterbalanced by the value of the steamship, which bears to that of the sailing-vessel per net carrying ton the proportion of 3: 1, thus reducing the ratio in favor of steam-shipping as 13·29 to 10·38, or in round numbers as as 4: 3. In testing this result by the charges of premium for insurance, the variable circumstances of distance, nature of cargo, season, and voyage have to be taken into account; but, judging from information received from ship-owners and underwriters of undoubted authority, I find that the relative insurance paid for the two classes of vessel represents an advantage of 30 per cent in favor of steam-shipping, agreeing very closely with the above deductions derived from statistical information.

In considering the question how the advantages thus established in favor of steam-shipping could be further improved, attention should be called in the first place to the material employed in their construction. A new material was introduced for this purpose by the Admiralty in 1876-'78, when they constructed at Pembroke dock-yard the two steam corvettes, the Iris and Mercury, of mild steel. The peculiar qualities of this material are such as have enabled ship-builders to save 20 per cent in the weight of the ship's hull, and to increase to that extent its carrying capacity. It combines, with a strength of thirty per cent superior to that of iron, such extreme toughness, that in the case of collision the side of the vessel has been found to yield or bulge several feet without showing any signs of rupture, a quality affecting the question of sea-risk very favorably. When to the use of this material there are added the advantages derived from a double bottom, and from the division of the ship's hold by means of bulk-heads of solid construction, it is difficult to conceive how such a vessel could perish by collision either with another vessel or with a sunken rock. The spaces between the two bottoms are not lost, because they form convenient chambers for water-ballast, but powerful pumps should in all cases be added to meet emergencies.

The following statement of the number and tonnage of vessels building and preparing to be built in the United Kingdom on the 30th of June last, which has been kindly furnished me by Lloyd's, is of interest as showing that wooden ships are fast becoming obsolete, and that even iron is beginning to yield its place, both as regards steamers and sailing-ships, to the new material mild steel; it also shows that by far the greater number of vessels now building are ships of large dimensions propelled by engine-power: