Maritime transportation logistics is concerned with the movement
of a set of cargos between seaports by means of a heterogeneous
ship fleet. It is fundamental to international trade as it
provides a cost-effective means to transport large volumes of cargo
around the world. It is estimated that over 80% of world trade is
carried by sea. The review of Maritime Transport, UNCTAD
(2011), details that during the first decade of the new millennium
the cargo carrying capacity of oil tankers grew by 60%, that of dry
bulk carriers grew by 65%, and containerships capacity more than
double (up to 164%). The growth of fleet capacity facilitates the fast
expansion of seaborne international trade that has increased by
40% during the same decade.
A fundamental topic in both chemical and shipping industry is
the cost-efficient management of heterogeneous ship fleets.
According to Christiansen, Fagerholt, Nygreen, and Ronen (2007),
a ship involves a major capital investment (usually millions of US
dollars, tens of millions for larger ships) and the daily operating
cost of a ship may easily reaches thousands of dollars and tens of
thousands for the larger ships. Proper planning of fleets and their
operations has the potential of improving their economic performance
and reducing shipping costs.
Broadly speaking, sea transport can be divided into tramp and
liner shipping. On the one hand, the purpose of tramp shipping is
to provide convenient and economical transport of bulk cargos that
require cross-ocean movement. The tramp ship can be any vessel
that does not have a fixed itinerary and go from place to place
depending upon where they can find cargos. Bulk cargos can be
classified into dry bulk and liquid bulk. Demand for the transport
of liquid bulk by sea is served mainly by the sector of tanker shipping.
Ships designed for the transport of liquid in bulk are called
tankers. The main cargos carried in tankers are liquid and gas. On
the other hand, a main function of liner shipping is to satisfy the
demand for regular transport under which cargos are transported
through regular routes and with regular schedules.
This paper focuses on tramp shipping that operates with a fleet
of heterogeneous multi-parcel chemical tankers. The challenge is
to spot the bulk cargos to serve and construct routes and schedules
that maximize the ship profit. A cargo consists of a specified quantity
of a given product that must be picked up at its port of loading,
transported, and then delivered to its port of discharge. The bulk
cargos shipped in large quantities are most oil tankers, but there
are also tankers carrying chemicals, liquid food products and other
commodities. In practical situations, transshipment cargos have a
time interval within pickup service must begin. Generally, a fleet