@ SASless,
Some sovereign nation issues a Letter of Marque to an NGO who then can legally conduct anti-piracy operations against designated targets described within the Letter, using defined limits, and all is above board.
As long as the ship is clearly marked and identifiable as being on government service, you meet the necessary requirements; except for weapons licences etc. I am sure something could be worked out.
Only problem is that in the area that the pirates operate from, the number of countries, the length of coastline is absolutely vast. Also, recognising boats on piracy raids is not easy. You end up with a large percentage of false positives. Think of the number of ships required.
What is required is continuous MPA (not just one aircraft either), aircraft/ helicopter carriers which provide fast access to suspect vessels, fast patrol ships and RIBs that are able to access the suspect vessels, whilst they are still under surveillance, and extremely good, current HUMINT, including when mother ships and small boats exit and access ports.
Mind you the numbers of vessels and aircraft required would be prohibitively expensive.
Remember, blockading ports wont work. Practically any piece of coastline can be used as a port for small vessels.
Hval