and one set further aft; this was why the Prince Consorts had two widely spaced funnels (one for each set of boilers). The Prince Consorts boilers were not of equal size. The forward set were larger and had five furnaces each, whereas the aft boilers had three furnaces each. "Each group of boilers had its own coal bunkers abreast it". "The boilers worked at 20 lb pressure." Cost of construction The following table compares the cost of construction of: Two-decker steam line of battleships of the Duncan-class. Had the Bulwark class been completed to their original design, their costs would have been similar. Wooden-hulled ironclad battleships of the Prince Consort class and their half-sister the Royal Oak. Iron-hulled ironclad battleships (the first seven laid down). The ironclads were much more expensive both in absolute terms and in cost per ton than the steam wooden line of battleships. The cost per ton of all the ironclads listed was similar, with Prince Consort the least expensive at £36 per ton, and Achilles and Valiant the most expensive at £48 per ton. None of the cost data in the table above includes the cost of armament. Data on Duncan and Gibraltar are taken from Lambert. The date of steam trials has been taken as the date of completion. Costs probably do not include "masts, sails, stores, &c., until complete for sea". Data on the displacement and construction dates of ironclads has been taken from Conways (except for 'laid down' dates for the conversions from the Bulwark class, which were taken from Lambert. Data on costs of ironclads are the "actual outlay on labour and materials" and were taken from Reed. The costs quoted by Reed are similar (but not always identical) to those quoted in Parkes. Baxter quotes similar but not identical costs for the first four British ironclads. Notes References Ballard, Admiral G.A. The Black Battlefleet, published Nautical Publications Co. and Society for Nautical Research, 1980. Baxter, James Phinney The Introduction of the Ironclad Warship, published Harvard University, 1933. Brown, David K. Warrior to Dreadnought, Warship Development 1860–1905, published Chatham Publishing, 1997. Clowes, William Laird Four Modern Naval Campaigns, Historical Strategical, and Tactical, first published Unit Library, 1902, reprinted Cornmarket Press, 1970. Conway All the World's Fighting Ships 1860–1905, published Conway Maritime Press, 1979. Lambert, Andrew Warrior, Restoring the World's First Ironclad, published Conway Maritime Press, 1987. Lambert, Andrew Battleships in Transition,