Therefore, additional feedwater was required, and it was supplied by apparatus such as an evaporator, as was fitted in , built by Palmers and launched in 1899. Each boiler had its own feedwater pump, and a feedwater regulator also of Reed's design. Another type of boiler similar to and later than the du Temple boiler was the Yarrow boiler, which usually dispensed with external down-comer tubes after its designer, Alfred Yarrow, demonstrated in 1896 that they were not essential to the circulation of water inside a boiler of this type. However, while the Yarrow boiler employed entirely straight tubes through which water and steam circulated more freely, it was considered by some contemporary writers on the subject such as Leslie S. Robertson as "behind" in its circulation because of the absence of down-comers. Whereas the Yarrow boilers fitted to the armoured cruiser of 1905 evaporated 11.664 pounds (5.291 kg) of water per pound (454 g) of coal at 100 degrees centigrade (212 degrees Fahrenheit) with natural draught, by the same measure a Reed boiler as fitted to the torpedo boat destroyer of 1896 evaporated 12 pounds (5.44 kg). An advantage of the Yarrow boiler was in weight: whereas the Reed boilers in the cruiser of 1897 produced 38.5 indicated horsepower (IHP) per ton (1016 kg) of boiler at full power, by the same measure the Yarrow boilers in a slightly earlier torpedo boat destroyer produced 73 IHP. But, whereas for example a torpedo boat destroyer of 1896 required four Reed boilers to achieve its specified top speed of 30 knots, a similar Swordfish-class vessel required eight Yarrow boilers to achieve its specified top speed of 27 knots. As fitted to torpedo boat destroyer in 1895, a dry Reed boiler weighed 13.25 tons (12.44 tonnes). A Reed boiler could be designed to operate at internal pressures of up to 300 pounds per square inch (2,068 kilopascals) and, as constructed for torpedo boat destroyers such as Spiteful, which was capable of steaming at 30 knots, a set of four boilers and associated machinery required nearly 25 miles (40 kilometres) of tubing. Overall, her four boilers each measured about long by wide and, from the platforms on which her stokers worked, known as "firing flats", about high. While each of eight Reed boilers in Pegasus had a grate area of about and a heating area of about , together they produced up to