Simply put, the Navigation School is a great replacement for the University. It offers all the same bonuses that the University does in addition to +1 Great Admiral point, +25% Production to naval units and +1 Science from every two Coast or Lake tiles in the Navigation School's city, all without being more expensive to build or maintain. Naturally, as Portugal, you will want all of your cities to be coastal, and this building puts another layer of emphasis on that, since none of its bonuses can be used consistently by an inland city.
The extra amount of Science can be really game changing if some of your cities are built on tiny landmasses surrounded by water. The total amount of Science can triple, or even quadruple the base Science granted by a University. Of course, not every city can generate a meaningful amount of bonus Science with this building, since it is perfectly normal to have coastal cities with very few coast tiles (especially ones on the coast of a large continent or landmass), but on average, it should have the same effects as having Isaac Newton, which is one of the most powerful and contested Great Scientists.
The Navigation School is also part of the Portuguese strategy to establish Feitorias across the map. The +25% Production towards naval units allows Portugal to build large numbers of Galleys when combined with the Press Gangs military policy card, which can then be upgraded with the Gold Portugal will be dripping in from their international Trade Routes (and which they can spend less of by slotting Professional Army right before upgrading) into Naus. This gives Portugal a spectacular mid-game push around the late Medieval to early Renaissance, when their Trade Routes become much stronger with policy cards such as Trade Confederation (unlocking at Mercenaries) and Wisselbanken (unlocking at Diplomatic Service). Having 2 Naus triggers the Inspiration for Exploration, which unlocks Merchant Republic, and allows for proactive construction of Feitorias in cities you're trading with. If you want to create a naval empire, this is the time to build the Venetian Arsenal as well, although between Press Gangs, the Navigation School, and any inherently productive tiles in a powerful coastal city, the Arsenal might be overkill and your time may be better spent just pumping out ships.
Sagres is the southernmost point in Portugal, the last safe shelter before ships would depart across the storm-tossed Atlantic. Looking south, Portuguese sailors faced rough seas and the forbidding “Cabo de Não” – “Cape No,” that stretch of the Atlantic coast of what is now Morocco where the Sahara begins. For long considered the end of the navigable world (hence the name) by European and Arab sailors, Cabo de Não (now called Cape Chaunar) had to be overcome for the Portuguese to realize their dream of a ship-based empire.
The planning for – and ultimate success of – Portuguese expeditions around the Cape, and around other, farther, more forbidding capes, happened at schools of navigation. While some scholars interpret this “school” term loosely, noting that most Portuguese sailors probably did their studying practically aboard ships, others posit a centralized school of navigation – placed by the most romantically-inclined scholars right at the Sagres Point. From here, sailors would be able to see firsthand the dangers of the Atlantic… and plot out ways to overcome them.
- The Navigation School's model is based on the main building of the University of Coimbra, the oldest and most prestigious university in Portugal. Ironically, the building currently belongs to its Law Faculty and the university itself historically has nothing to do with navigation. João III moved the university, originally founded in Lisbon, to Coimbra definitively in 1537, and a statue of him still stands today in the school's main courtyard.