Do they defend individual ships and ride aboard, or do they freelance? The pirates take a ship and demand ransom, and Blackwater takes the ship back, killing all the pirates aboard and sailing the ship back to the open ocean. If the company pays Blackwater half the usual pirate ransom for their freelance work, the next ship gets rescued too at the same rate, and otherwise Blackwater blacklists that company. I like it, and I imagine a few Blackwater professionals would like hunting down pirates better than riding security duty.
The alternative? Hopefully if Blackwater does ride security, they'll stay low-key. When the pirates show up, Blackwater could follow a "don't fire until you see the whites of their eyes" strategy, and we'll still get lots of dead pirates. The best part of that is that dead men tell no tales - and they might all be within range of Blackwater's weapons. The pirates might be slow to figure out what's going on, and they could lose a large percentage of their experienced leaders before they realize that the rules have changed.
I'd recommend against 'freelancing'. Leave that to the Navies. I'd defend individual ships and ride aboard. A squad and their gear could be helicoptered to ships entering the target zone.
They could surreptitiously install a couple of .50 cals in temporary mounts, put a couple of sniper teams on top of the bridge, and then just wait.
A small per diem would be charged, say $10,000 per man per day, until there was a confirmed kill of a pirate crew. Then the price would go up to a million or so.
A six or seven man team should do it I would think.
The shipping companies would write it of as a CODB. It's either cheap insurance at say 150 to 200K per trip. The sight of pirates being chopped to pieces and their ships sunk would be a fairly strong deterrent.
If there's anyone left with any cojones in the Administration a coordinated Seal or Delta strike on the HQ's of these pirate gangs (I can't believe we don't already know who and where they are.) leaving piles of dead and smoking ruins of their new mansions would also send a powerful message.
Then the Somalis can go back to starving each other to death.
Problem solved in about 6-8 months and Blackwater gets a healthy infusion to their bottom line.
L