To me it appears that the forces arrayed in the Indian Ocean to deal with the pirates are not suited to the job. Destroyers, frigates and the like are not suited to chasing fast skiffs or similar fast motor vessels, they are designed to fight large scale 'formal' wars.
At the start of WWI there was no easy way to engage submarines. This led to the creation of the 'Q' Ship. This was a medium sized merchant vessel, crewed by the navy, armed with a number of consealed quick firing guns. The ship was chosen to be just too small to be worth a torpedo, so the sub would surface to try and capture and scuttle it, or sink it with fire from the sub's deck gun(s), whereupon the 'Q' Ship would engage the sub with its weaponary. It proved moderately successful.
I would think a number of 21st century versions of such 'Q' Ships may prove a major deterrent against Somali pirates who are preying on merchant vessels. Perhaps such things should be deployed.