Since the 19th century, due to the Convention Wars with England, and the Carlist Wars, in which the Fleet registered in Plentzia practically disappeared, Plentzia sailors, enrolled in ships from other ports, were present especially in trade with Andalusia, England, Caribbean and Philippines.
All aspects of navigation were governed by the Brotherhood of Seafarers (Cofradía) of Plentzia, called San Pedro, which also brought together the sailors of Barrika, Sopela, Lemoiz and Gorliz. Its oldest ordinances date back to 1524. The Brotherhood became extinct in 1870.
The Cofradía promoted the Plentzia Nautical School, which operated from time immemorial and existed until 1933. Also in the 20th century, the Customs House, the Regional Court and the Navy Assistant disappeared.
Due to the excellent quality and quantity of the wood in its forests, the existence of shipyards has been known since the beginning of the town, in the place where the so-called square is currently located, as it appears in the Delmas engraving from the middle of the 19th century. The shipyards disappeared after the Second Carlist War, in the last third of the same century.
The estuary has been decisive in marine development, the poet Ramón de Basterra wrote about it and the museum shows a model layout. The draft problems aggravated by the construction of the outer docks at the beginning of the 20th century, the channeling of the estuary and the road to the Marine Sanatorium, have diminished and varied the old topographic profile.