The most common size of sail ship of the line was the "74" (named for its 74 guns), originally developed by France in the 1730s, and later adopted by all battleship navies. Until this time the British had 6 sizes of ship of the line, and they found that their smaller 50- and 60-gun ships were becoming too small for the battle line, while their 80s and over were three-deckers and therefore unwieldy and unstable in heavy seas. Their best were 70-gun three-deckers of about 46 metres (150 ft) long on the gundeck, while the new French 74s were around 52 metres (170 ft). In 1747 the British captured a few of these French ships during the War of Austrian Succession. In the next decade Thomas Slade (Surveyor of the navy from 1755, along with co-Surveyor William Bately) broke away from the past and designed several new classes of 51- to 52-metre 74s to compete with these French designs, starting with the "Dublin" and "Bellona" classes. Their successors gradually improved handling and size through the 1780s. Other navies ended up building 74s also as they had the right balance between offensive power, cost, and manoeuvrability. Eventually around half of Britain's ships of the line were 74s. Larger vessels were still built, as command ships, but they were more useful only if they could definitely get close to an enemy, rather than in a battle involving chasing or manoeuvring. The 74 remained the favoured ship until 1811, when Seppings's method of construction enabled bigger ships to be built with more stability.