A hemmema ( from Finnish " Hämeenmaa " , Tavastia ) was a type of warship built for the Swedish archipelago fleet and the Russian Baltic navy in the late 18th and early 19th centuries . The hemmema was initially developed for use against the 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 .