I don't know. If you wanted to dismay your friends and add a few new enemies I don't think you could do much better than Israel did yesterday morning. AS I understand it, in international waters (aka the "high seas"), you are governed by the laws and regulations of the country whose flag you are flying/country of registry of your vessel. You can be boarded by the authorities of that country but in theory no-one else.
If you are flying no flag/do not have a clearly defined country of registry, then you are de facto a pirate and can be boarded/challenged by any naval vessel.
Those Turkish ships hardly fall into either category vis a vis the Israeli navy. Attacking vessels on the high seas is piracy, isn't it ?
It's not as if the boats were carrying arms. Cement isn't a deadly weapon. And no matter who did what on the boats, the IDF had no right to be there at all.