Fredrik Henrik Af Chapman - in Swedish Service

In Swedish Service

In 1757, Chapman was made assistant shipwright at the royal dockyards in Karlskrona at the age of 36. Soon after his appointment, he drafted his ideal plans for docks, which included facilities for properly ventilated sail storage and advanced dock pumps that could be powered by human power, horses or wind mills. The plans would, however, not be realized until much later, when Chapman was made chief shipwright of the Karlskrona yards.

In November 1758 to April 1759, he was charged with a timber inspection cruise along the coasts from Turku up to the Gulf of Bothnia. Later, Chapman moved first to Stralsund (then a Swedish possession) where he stayed until 1762, and later to Sveaborg where he stayed until 1764. His first major assignment came in 1760. The recently-formed archipelago fleet (skärgårdsflottan), an inshore fleet independent of the navy under the command of the army, was in need of new vessels to replace the galleys which had proved problematic in the war against Prussia that had broken out in 1757. The commander of the archipelago fleet Augustin Ehrensvärd and the man in charge of the construction of the new naval base and fortress of Sveaborg began a successful collaboration with Chapman in designing new types of what would later be called "archipelago frigates" (skärgårdsfregatter). Inspired by Russian "chebecks" (variants of Mediterranean xebecs, hybrid sailing ships that incorporated features of galleys), the two created craft that could be rowed, but with heavier armament and additional protection for the crew, a necessity in the cold Baltic climate. The cooperation resulted in four new types of archipelago frigates: udemas, pojama, turuma and hemmema, all named after the Finnish names of Swedish provinces in Finland, the coasts of which they were intended to protect.

By closely examining drawings of ships with known good sailing qualities Chapman realized that the framework should be divided in a certain progression. The frames should decrease from the place of greatest width in the same relation as the ordinates 0, 1, 2, 3, 4 etc (pictured), where the arc ABC is a parabola, AD is the axis and A is the vertex (the "peak"). This construction method is called the "parabola method". Chapman also introduced the so called "relaxation method", but preferred the former himself.

At Sveaborg, Chapman supervised and led the construction and expansion of the naval yards, including cranes, docks and various buildings. He moved to Stockholm in 1764, but remained in charge of the design of vessels for the archipelago fleet. He was also made a part of a commission that was to propose improvements on the expansion of the high seas navy. Its final report was presented in 1764 and recommended new designs for standardized ships of the line varying from 50 to 70 guns. The report represented the ideals of a new school of shipwrights that favored scientific methods and the use of theoretical models at early stages in ship design, a view that was in conflict with the old school of shipbuilding which favored slow evolution based on practical experimentation. The old school, represented most prominently by Gilbert Sheldon, came into conflict with the new ideas, but lost the debate when the Board of the Admiralty favored the findings of the commission at the Riksdag in March 1769 and put Chapman in charge of designing the navy's new warships.