  Ports are striving for innovative technological solutions to cope with the
increasing growth in demand of goods transport, while at the same time
improving their environmental footprint. An emerging technology that has the
potential to substantially increase the effectiveness of the multifaceted and
interconnected port processes is that of digital twins. Innovation-leading
ports recognizing the potential of twinning have already started working on it.
However, since there is no clear consensus on what a digital twin of a complex
system comprises and how it should be designed, deployed digital twin solutions
for ports often differ significantly. This article addresses this issue by
initially identifying three core aspect underpinning digital twins of complex
systems, such as ports, and outlining five successive maturity levels based on
these aspects' instantiation. These identified aspects and the derived maturity
levels are then used to examine real-world cases by critically evaluating
existing digital twinning solutions in the port of Singapore, the Mawan port of
Shanghai, and that of Rotterdam. These being three of the world's
innovation-leading ports, we naturally find in them most of the identified core
aspects to be in line with their twinning implementation, which has reached, in
all three, a higher level of maturity. Although, our work on maturity levels
and core aspects can provide a guideline for designing and benchmarking future
digital twinning solutions for ports, the capacity for innovation via twinning,
even in the port domain, is highly contextual with key paragon being the
availability of financial and technical resources.
