I'm with Alfred the Great on this one. Unless we tackle the roots of the problem we are wasting our time. The ship owners and the Somalian 'Mr Bigs' in all know that its cheaper to pay the ransoms than risk having an RPG through the side of a tanker. Arming merchant ships is still likely to result in more death, injury and detruction to their crews and cargoes on them than the ship owners are willing to tolerate.
Given that the pirates have already tried to hijack a US navy vessel, they are obviously not the brightest candles on the birthday cake, and for America to throw them into a US jail for life is just going to cost the US taxpayers a lot of money, whilst Mr Big just recruits the next lot of poverty-stricken teenagers willing to try anything.
Capturing one or two of the Mr Bigs, so they can have the error of their ways pointed out to them, or taking them out with a UAV if there is enough evidence against them, together with making every effort to improve life for Joe Average in Somalia is the only way this will stop. Of course it isn't easy, otherwise it would already have been done.