Another important route for British shipping was to the antipodes in which Brunel again played a part. His designs in 1852 for the Victoria and the Adelaide both had detachable screw propellers enabling the ships to economize on fuel by availing themselves of the plentiful and more-or-less free wind to be had on their voyages out to Australia. The Victoria blazed the trail from Gravesend to Adelaide in sixty days, less than half the time normally taken under sail alone. Between 1840-50 the great majority of the 520 similar passage under sail took 120-130 days.
A major improvement in steam technology that assured its potential for limitless efficient and economical travel was the development of compound engines in the 1860s. The main thing remaining very much to the disadvantage of iron hulled, screw propelled steamships on long journeys was the cost of fuel. The breakthrough came with compound steam engines whose refinement ultimately led to the consumption of half the fuel of the old simple-expansion engines. Compound engines were also smaller and lighter thus leaving more space for cargo. In 1860 there were still roughly seven tons of sailing ship to every ton of steamer. The proportion would have been even more in favour of sail were the inland waterways and lake steamers to be excluded. Apart from everything else, passenger travel by sail was cheaper than by steam. But the new compound steam engines changed all that and the tonnage of steam ships built compared to sail advanced rapidly over the decade between 1860 and 1870 such that by 1880 the tonnage of new steam ships was approximately eight times that of sail. Their greater efficiency not only meant less fuel used but fewer stops required for bunkering and greater distances achievable. England to Mauritius, 8,500 miles away, was achievable by 1870 without stopping for bunkering and the future of steam was assured.
Ships were almost all made of wood till the middle of the 19th century. With booming iron and steel production, particularly in Britain where the supply of timber was essentially exhausted, first hulls then masts and spars were made of iron from 1865-1885. Thereafter steel was preferred as cheaper and easier to work. Leaving aside such batty objections that long journeys would be rendered impossible by having the sun on one side so long that ships would become banana shaped and thus impossible to steer, iron hulls, contrary to what many others intuitively thought, not only floated but were indeed lighter, and therefore faster than their timber equivalents. Iron, being also considerably stronger than timber, enabled ever bigger ships to be constructed. Timber hulls required considerable amounts of internal bracing to strengthen them whereas iron construction was internally much more open providing relatively greater stowage space and accommodation. A great advantage of iron and steel hulls from the men's point of view was that they did not leak - unlike wodden hulls which usually did and required constant manning of the pumps.
Iron hulls could withstand fire whereas wooden hulls could not. The Cedarbank survived being on fire in 1893 for 36 days whereas it was reckoned, had she been wooden, she'd have sunk in three. In 1876 the Ada Iredale was abandoned in the Pacific with her cargo of coal alight. She was picked up after being adrift for eight months and towed to Papeete where the fire was finally extinguished in May 1878. She was then refitted, renamed Annie Johnson and sailed for many more years.
The added strength of iron also enabled ships to withstand collision better than wooden ships, particularly if the ‘other’ ship was wooden, and iron hulls were easier to repair than their timber counterparts. Likewise, iron ships survived going aground better, sustaining less damage in the first place and again being more easily repaired. The Antiope was aground for 96 days in surf off Bluff Harbour, N.Z. in 1916 when she was already 50 years old. Demand for shipping in WW1 so great she was subsequently floated off, repaired and sailed for another 5 years before being abandoned on fire. However she remained afloat and was still being used as a store ship as late as 1927.
Double hulls and watertight bulkheads developed with iron and steel construction and meant that iron ships were eventually much safer than timber ships ever could be. But never forget the Titanic! Iron was also cheaper than timber; in the 1830s for example it was £3 a ton cheaper to build using iron. Finally iron was more-or-less unlimited in supply, whereas timber was not, the bulk of it in the U.K. eventually having to be imported. I don't have figures for 19th century merchant ships, but some idea of the quantities of timber required can be gained from the fact that in the mid 18th century a typical 74 gun Third Rater required roughly 3000 trees. Such vessels would typically have been about 50 feet shorter than the British Princess. Another consideration in building was the great cost of masts. A barquentine was square rigged on her foremast and fore-and-aft rigged on all the others. It was said that the foremast of a four masted barquentine cost as much as the other three masts.
All the early steam ships had wood hulls and paddle-wheels; even as late as the 1860s this remained largely the case although some iron-hulls such as the Pacha had screw propellers. Before steam became self-sufficient, paddle-steamers made use of wind whenever possible or favourable, but the paddles were an encumbrance. There were also completely different design criteria for inland or coastal vessels compared with ocean going vessels. Bunkering space on the former did not need to be extensive as supplies of fuel were always comparatively near at hand. Neither did the hulls of inland and coastal vessels have to be constructed to withstand anything like the rigorous conditions found in crossing the oceans. The extra costs involved, combined with loss of cargo capacity due to the exigencies of bunkering, meant that while the technology was capable of keeping pace with the demands, the economics did not. The British and American Steam Navigation Co. concluded that “...it was virtually impossible for any North Atlantic steamship line to continue in existence without a subsidy.” - before going bust in about 1840 thereby proving their point. Thereafter subsidies were awarded.
Although iron inevitably gained the argument over timber it still only represented ten percentage of the tonnage of all new ships launched in British yards in 1850. Ten years later timber was still being used, especially in America and Canada which had vast timber resources but comparatively small iron production, but generally iron was firmly in the ascendant with seventy percent of the new build tonnage. The swing to iron hulls was not exclusive to steam; the same advantages conferred by its lightness and strength relative to timber, and the increased size of vessel made possible applied equally to the construction of sailing ships. So sail sailed serenely on, and continued to be profitable.
There were some problems with using iron for shipbuilding one being the effect on the ship's compass, which was swiftly overcome by using compensating magnets placed in the binnacle. A much greater problem and one that has never really been solved is serious fouling - the accumulation of marine growths on the hull, principally barnacles and weed, which leeds to a considerable loss of speed and efficiency. This was eventually controlled by the development of anti fouling paints which inhibited but never fully prevented marine growth, much to the delight and satisfaction of manufacturers of marine paints.
Fouling of wooden hulls was much reduced or even eliminated by sheathing in copper - hence ‘copper bottomed’. Iron and steel are very susceptible to fouling. In 1869 the iron Carlisle Castle left Calcutta for London a month before Windsor Castle, a wooden copper bottom. Windsor Castle arrived a whole month ahead of Carlisle Castle purely on account of the Carlisle Castle's impaired speed due to fouling - a difference of 2 months on a 4 month voyage! Ribbon weed could grow 3 to 4 feet long making a ship almost impossible to tack. Barnacles accumulate in huge profusion. The Daylight had 40 tons of barnacles removed in 1908.
Iron sailing ships looked different to their wooden counterparts; in the 1870s they were longer but less beamy and with less freeboard for their tonnage. There were many other differences to the seasoned observer, but for all that they were made of iron they did not lack beauty and grace of line and many were lavishly ornamented with decorative detail. Sailors could generally identify the nationality of a sailing ship by its rig. They could also identify many British makers on sight.
The first steel as opposed to iron ship was the 1283 ton barque Altcar built in 1864 by Jones, Quiggan and Co. Liverpool. From 1882 steel became the preferred material and was used in four of the year's finest ships, the Garfield, the Helenslea, the Sierra Parima, and lastly the Pinmore which was to achieve additional fame, first by accommodating Felix von Luckner before the mast in 1902 before he returned in 1917 to capture her and take command from the other end of the ship and ultimately send her to the bottom. While iron lasted longer, steel was stronger, lighter and cheaper - so end of contest.