The right to stop and search at sea?

My understanding of international law (inasmuch as such a concept exists) is that boarding a vessel by force on the high seas is an act of piracy, unless the two countries involved are at war. Israel has been very careful not to declare war on Gaza because that would mean, among other things, that they would have to comply with the various rules and conventions which govern the conduct of warring parties. So what Israel did was piracy, pure and simple. Why didn't they just wait until the ships were within the twelve mile limit before boarding them? They could then at least have made some sort of a case for saying that they were within Israeli territorial waters. Is this just another example of their macho posturing - "We did it because we could"? And did nine people have to die to prove their point?