Sea battle July 27, 1720, the Battle of Grengam, is most ambitious battle of galley fleets in the Baltic during the Great Northern War (1700-1721). The study of two previously unused 18th century Swedish drawings by Russian historians from the Maritime Museum in Karlskrona (Sweden) shed new light on a number of controversial issues. This is the composition and battle line ahead of the Swedish squadron Admiral K. G. Sjöblad, which attacked the Russian galley fleet under the command of General M. M. Golitsyn. The fact of the attack of 23 or 24 Russian galleys in the rear of the advanced part of the Swedish squadron was confirmed. It is shown that the second part of the Swedish squadron did not take a real part in the battle. It is revealed that both Swedish drawings along with valuable information contain Swedish propaganda fiction.