There were vessels and boats of all kinds and for all sorts of purposes during the Middle Ages. There were small fishing boats as well as large merchant ships.The boats were rowed or sailed. Some ships had only one mast with one sail, but during the 15th century, vessels were built which measured 50 metres, with up to four masts with many sails on each mast.
Different kinds of ships from many countries sailed on the Baltic Sea. The larger vessels, the cogs and the hulks sailed across the open sea to the ports. With a compass and with favourable winds, they could sail straight across the Baltic Sea to and from Lübeck, Kalmar, Visby and Riga. If the wind dropped, or if there were storms, the captain and his crew had to stay in the harbour and wait for better weather. They had to be patient - the most important thing was to get the valuable cargo safely across the sea.
Between the towns and settlements on the coast, smaller vessels were used. Land-marks, such as mountains or buildings, cairns or beacons, showed the way along the coast. To avoid running aground, the depth of the water was measured by a lead, a cord with a weight at the end.
The harbours in the towns were busy, crowded places. Merchants and skippers made contracts about voyages to foreign ports. Goods was taken to the waiting ships. Sailors said goodbye to their wives and children who they would not see for months. The sailors had a difficult and sometimes dangerous job. Many people depended on them to transport valuable goods safely across the seas.