When sailing along Venetian trading routes, our captain will use GPS and computerised maps. The Venetians however had to do with Astrolabes and a few, if any, in-accurate maps. The astrolabes allowed them to determine their latitude by measuring the inclination of the sun, the planets or well known starts. Determining the longitude was a guessing game and only resolved by the development of accurate chronometers in England in the 17th century. Thus ships in the Middle Ages had to follow the coast.
One of the Astrolabes used in the Mediterranean
The name of Astrolabe in Greek actually means “star catcher”. The instrument was developed by Indian and Arab astronomers and used in the Mediterranean as early as the 8th century. It was quickly copied by the European maritime powers of Genoa and Venice. Every Venetian ship had an Astrolabe on board.
This one was made in the Middle East and was probably used in the Turkish Navy