True, and looks like the portuguese may only have been inspired to sink the initial R&D into disruption because the ottomans, having taken Constantinople, were charging* too much as gatekeepers:

https://en.wikipedia.org/wiki/Portuguese_discovery_of_the_se...

Lagniappe: https://en.wikipedia.org/wiki/Mare_clausum#/media/File:Iberi... (can you spot Brazil in this projection?)

EDIT: note also how the Treaty of Alcáçovas (1479) drew a line across the Atlantic which is still largely conserved by the sea boundary between USEUCOM and USAFRICOM

* EDIT2: could they have charged just enough to make the age of exploration look risky and too expensive, not risky but potentially cheaper?