  Maritime monitoring systems support safe shipping as they allow for the
real-time detection of dangerous, suspicious and illegal vessel activities. We
present such a system using the Run-Time Event Calculus, a composite event
recognition system with formal, declarative semantics. For effective
recognition, we developed a library of maritime patterns in close collaboration
with domain experts. We present a thorough evaluation of the system and the
patterns both in terms of predictive accuracy and computational efficiency,
using real-world datasets of vessel position streams and contextual
geographical information.
