Several years ago the
Republic of Singapore Navy
retired the RSS Sea Dragon
and five of her sister missile
gunboats (leftmost image)
after over 30 years of service
each. Depending on
economics and staffing, it
might be attractive to
recommission these veterans.
They need not be crewed with
100% Republic of Singapore
sailors and officers. The
intent was to locate them at
strategic points along the
Malacca Straits to act as
radar pickets. Note that we
are NOT assuming pirates are
the only threat. Terrorists
would likely prefer to sink
one ship and have hundreds
of extortion payments made
by direct deposit.
Maybe a speedy pirate can outrun a frigate or even a faster (at least 40
knots) unmanned vessel (above). Of course, the clever pirate must also
evade a corvette's guns.  Dramatic as American
Iowa class battleships
(top right) were, their 16 inch guns are the wrong tool against pirates.  
No pirate can outrace a missile, whether it is launched from a ship, a
helicopter or from shore.