I pointed out up above that an arms race with the pirates is a bad idea. There's not a tanker crew alive who want their ship to be hit with RPGs, and they are kid's stuff compared with hand-held anti-tank weapons, which could punch a hole in ANYTHING that you build a commercial ship out of, and then explode inside. The pirates are reportedly tooling up from the arms dealers.
I should think that the only military solution is motor-gun-boats, bigger and better-armed than the opposition.
Now, if only there was a navy with some to spare!
Probably get some from arms dealers?