A hemmema (from Finnish "Hämeenmaa", Tavastia) was a type of warship built for the Swedish archipelago fleet and the Russian Baltic Fleet in the late 18th and early 19th centuries. The hemmema was initially developed for use against the Imperial Russian Navy in the Archipelago Sea and along the coasts of Svealand and Finland. It was designed by the prolific and innovative Swedish naval architect Fredrik Henrik af Chapman (1721–1808) in collaboration with Augustin Ehrensvärd (1710–1772), an artillery officer and later commander of the Swedish archipelago fleet. The hemmema was a specialized vessel for use in the shallow waters and narrow passages that surround the thousands of islands and islets extending from the Swedish capital of Stockholm into the Gulf of Finland.
The hemmema replaced the galleys that had made up the core of the Swedish archipelago fleets until the mid-18th century. Compared to galleys, the hemmema had a deeper draft and was slower under oars, but offered superior accommodation for the crew, carried more stores, was more seaworthy and had roughly ten times as many heavy guns. It could be propelled by either sails or oars but was still smaller and more maneuverable than most sailing warships, which made it suitable for operations in confined waters.
Between 1764 and 1809, Sweden built six hemmemas. The hemmema became the largest and most heavily armed vessel in the archipelago fleet and served in the Russo-Swedish War of 1788–90. Oden, the first hemmema, was relatively small and very similar to a turuma, a different type of "archipelago frigate". Russia built six hemmemas based on the Swedish design between 1808 and 1823, after capturing three of the Swedish vessels at the surrender of Sveaborg in 1808. The later versions, both Swedish and Russian, were much larger and much more heavily armed than Oden.