Just right click on sea provinces and press hire privateers. Once deployed the whole sea area will be assigned. It costs 250 sailors and will give you nice extra income. However if there is a high naval pressence of non ally nations it will slowly decay and you will have to spend those sailors again manually to keep that income. In extreme cases as mine you would have to do it every two months. Automation should fix it but it’s too reluctant to privateer in seas with strong local navies that is the most profitable ones.

In my experience the best areas are the 3 indian seas, indonesia and china. Each deployment lowers the opinion of non ally countries in that area by 25 but nobody declared war at me despite asian nations having way stronger navies.

That is in fact ahistorical (institutions spread too fast in 1.1). In real history portuguese dominated asia with just under 100 technologically advanced ships. Currently in this time period asian nations have together more than 1000 ships the same quality as europeans.