Law of the sea
However, the resolutions that made these actions permissible (1838 and 1846) also contain restrictions.
Everything has to be done in accordance with "international law" and this is interpreted as complying with the conditions of the International Law of the Sea Convention.
This convention, in article 105, does permit the seizure of a pirate ship, but article 110 lays down that, in order to establish that a ship is indeed a pirate vessel, the warship - and it may only be a warship - has to send a boat to the suspected ship first and ask for its papers.
This is hardly a recipe for a Denman or Decatur-type action.
Add to this legal restriction the relative lack of warships in the seas off Somalia - more than there were, but still insufficient - and the reluctance to tackle the pirates in their home bases, throw in the chaos in Somalia, where there is no effective government, and you have perfect conditions for piracy.
Even if they are caught, they are simply handed over to Kenya whose legal system is not designed to deal with them.
The German navy transported another batch of captured pirates to Kenya recently. But nobody knows how long they will be in custody there.
And the UN Monitoring Group on Somalia issued a damning report last December in which it castigated ship owners for paying ransom.
"Exorbitant ransom payments have fuelled the growth of [pirate] groups," it stated.
The report also expressed concern about "the apparent complicity in pirate networks of Puntland administration officials at all levels."
Puntland is a self-declared autonomous region of Somalia, right at the tip of the Horn of Africa.
(Update: The French have adopted a different policy - that of trying to rescue hostages and capturing pirates, taking them back to France for trial. This was successful until recently, when commandos stormed a yacht and in the process the yacht's owner was killed, though his wife and young son were rescued.)
Since writing in December last year about the legal problems involved, I have had a lot of e-mails from people angry at the ineffectiveness of the measures taken so far and proposing their own solutions.
These include:
Convoys. Already done in the case of aid ships going into Kenyan and Somali ports
Arming the crews. The crews might not want this, though in the latest case the American crew of cargo ship Maersk Alabama did fight back
Arming merchant ships with heavy guns. Ship owners might not want to risk an engagement at sea
luring pirates into attacking apparently unarmed ships which then declared themselves as warships. Would this be in "accordance with international law"?
Other ideas suggested would appeal to officers Denman and Decatur.
(Update: I have had a flood of further e-mails, for which many thanks. The plans proposed range from having submarines on stand-by to surface when needed, to 'Q-ships' (armed, disguised merchantmen), to immediate sinking, to blockades, to invasion. The general feeling is that governments and navies are too weak. There have been a few writers, though, who say that the real problem is in Somalia itself and that the pirates take to their trade because they cannot make a living in other ways.)
Paul.Reynolds
-INTERNET@bbc.co.uk