The first hydrographic scientific atlas of the peninsula was created by Vicente Tofiño de San Miguel. It could be said that this is the most significant cartographic production of the XVIII century and the base for modern cartography. It combines land observations, maritime, astronomic, and geometric. The atlas is of such cartographic accuracy that Nazi Germany used it during World War II to navigate their submarines.
The most critical problem of the port for centuries was the moving sandbar in Portugalete. Perpendicular to the mouth of the estuary, this sandbar would only leave a depth of 90 cm when low tide, and people were able to cross from Portugalete to Las Arenas walking. The location of the sandbar used to change every day, making the entering and exiting of the boats more difficult as they had to wait for the ideal combination of spring tides, calm sea and favourable wind to enter or exit. Until 1883, the port could only be used for 200 hours a year.
In order to look after the entrance and exit of the ship when passing over the sandbar, there was the Head Pilot of the Sandbar. Amongst his duties, there was to take a sounding every day and inform the boats waiting to leave of the depth of the water.
