@dogmush: as one of the ignorant -- thanks for not saying stupid -- I appreciated the lesson. I still think heavily armed and armored decoy ships is part of the solution in Somalia. (another part is to somehow get China to stop illegally fishing the Somali coast, and the EU dumping toxic waste there) But we're not talking about Somalia...
It can be, although in practice it has limited success. I personally think it's because, as much as you read about Piracy of the Horn of Africa, the ships nabbed as a percentage of ships in the region is pretty small, so the decoy ship just doesn't get attacked very often. And you can't have it just troll back and forth because then it's obviously not a merchant ship.
The most effective piracy deterrent in that region is armed private security teams on board ships. Usually it's just a team with small arms (up to like .50cal/12.7mm) and they are only on the ship for the transit, but they pretty effectively fight off the small boarding crafts the pirates use. There's also some physical measures that merchant ships can do to make themselves harder to board. This has worked well for the ships and companies willing to spend the money and effort. These days, the ships getting nabbed are the smaller, poorer vessels from countries that no one cares about.
The waters off the Horn of Africa also have pretty heavy anti piracy patrols from PRC, Russia, US, EU powers, Iran, and the KSA. That deters piracy against ships they care about. It's still not a great place to be a 300ft Liberian flagged ship crewed by Malaysians.
