Hydra was relatively unimportant during much of the period of Ottoman rule. Its naval and commercial development began in the 17th Century, and its first school for mariners was established in 1645. Apparently, the first truly Hydriot vessel was launched in 1657. However, the conflict between the Republic of Venice and the Ottoman Empire limited the island's maritime development until after 1718 and the Treaty of Passarowitz. From the 17th Century on, Hydra began to take on a greater importance due to its trading strength.
During the first half of the 18th Century, Hydra built the same kind of vessels as were built in the other Aegean Islands. These were the sachtouri of 15 to 20 tons, and the latinadiko of 40 to 50 tons. The Hydriots contented themselves with trading in the Aegean, going as far as Constantinople. The great change occurred in 1757 after they launched a vessel of 250 tons. The larger boats enabled Hydra to become an important commercial port. By 1771, one could count up to 50 vessels from throughout Greece in the roads. Ten years later the island had fitted out 100 vessels.
However, the Ottoman Empire and its policies constrained Hydra's economic success. Heavy tariffs and taxes limited the speed of development. The Ottoman administration limited free trade; the Ottomans permitted only Ottoman vessels to navigate the Dardanelles and the Bosphorus, and hence have access to the Black Sea, its ports, and the trade in grain from their hinterlands. The Treaty of Küçük Kaynarca changed all this. Russia gained from the Ottoman Empire the right to protect the Empire's Orthodox Christians. The religious protection had a commercial corollary: the Hydriots began to sail under the Russian flag. The Treaty also provided for free passage between the Aegean and the Black Sea. Hydra entered its commercial era. Hydriot vessels carried goods between Southern Russia in the east to the Italian ports of Ancona and Livorno in the west
