Evaluating the trade-off between the level of customer service and transportation costs in a ship scheduling problem

In many ship scheduling problems, time windows are imposed at the loading and/ or discharging of the cargoes to be lifted. Up until now, all proposed solution methods to ship scheduling problems have treated the time window constraints as hard constraints. By transforming the time window constraints into soft constraints, some of the loading/discharging operations may be performed outside the time windows, penalized by an inconvenience cost for not meeting the time window. The motivation behind introducing soft time windows is that, by allowing controlled time window violations for some customers, it may be possible to obtain better routes and significant reductions in the transportation costs. The purpose of this paper is to evaluate the trade-off between transportation costs and the time window violations. Computational results based on data from a real ship scheduling problem are presented and used as a basis for the evaluation.     

Routing and scheduling of RoRo ships with stowage constraints

Roll-on/Roll-off ships are used for international transport of vehicles and other rolling equipment. We consider the problem where a ship sails between two geographical regions, picking up cargo in the first and making deliveries to the second. Several variations are considered with optional cargoes, flexible cargo quantities, and ship stability restrictions. Decisions must be made regarding the route and schedule of the ship as well as the stowage of cargo onboard. The problem is modeled as a mixed integer program, which has been solved using Xpress. In addition, a tailor made heuristic procedure is built using components from tabu search and squeaky wheel optimization. Extensive computational results are presented, showing that the heuristic is able to handle realistically sized problem instances.     

Fleet deployment in liner shipping: a case study

The fleet deployment problem is an important planning problem in liner shipping. It deals with optimally assigning voyages to available vessels in the fleet and determining vessel routes and schedules in a way that minimizes costs or maximizes profit. This paper presents a new model for a fleet deployment problem in liner shipping, and we also propose a multi-start local search heuristic to solve the problem. The heuristic has been embedded in a prototype decision support system (DSS) that has been implemented and tested at Höegh Autoliners, a major global provider of ro-ro (roll-on roll-off) vehicle transportation services. The heuristic was able to produce high-quality solutions within a few minutes to a real planning problem with more than 55 vessels and 150 voyages over a planning horizon of 4–6 months. Tests indicated that the solutions suggested by the DSS gave between 2 and 10% improvements compared with solutions from manual planning. What is almost equally important is that using the DSS can ease the planning process.     

Evaluating the trade-off between the level of customer service and transportation costs in a ship scheduling problem

In many ship scheduling problems, time windows are imposed at the loading and/ or discharging of the cargoes to be lifted. Up until now, all proposed solution methods to ship scheduling problems have treated the time window constraints as hard constraints. By transforming the time window constraints into soft constraints, some of the loading/discharging operations may be performed outside the time windows, penalized by an inconvenience cost for not meeting the time window. The motivation behind introducing soft time windows is that, by allowing controlled time window violations for some customers, it may be possible to obtain better routes and significant reductions in the transportation costs. The purpose of this paper is to evaluate the trade-off between transportation costs and the time window violations. Computational results based on data from a real ship scheduling problem are presented and used as a basis for the evaluation.     

Designing optimal routes in a liner shipping problem

A real liner shipping problem of deciding optimal weekly routes for a given fleet of ships is considered and a solution method for solving the problem is proposed. First, all feasible routes for each ship are generated together with the cost and the duration for each route. The routes are given as input to an integer programming (IP) problem. By solving the IP problem, routes for each ship are selected such that total transportation costs are minimized and the demand at each port is satisfied. The total duration for the routes that are selected for a given ship must not exceed one week.

The real liner shipping problem is solved together with four randomly generated test problems. The computational results show that proposed solution method is suitable for designing optimal routes in several liner shipping problems.     

Planning vessel air emission regulations compliance under uncertainty

In this paper we consider the reduction of air emissions from vessels when uncertainty is taken into account. Uncertainty in the reduction effects of the different existing air emission controls is currently high and makes their selection for vessel emission regulations compliance a challenging process. We develop a two-stage stochastic optimization model that addresses this uncertainty. The model’s objective is to plan the installation of air emission controls over a specified time horizon for a vessel to comply in the most cost-efficient way with the air emission regulations. The uncertain reduction effects of the controls are modelled by a set of scenarios. The approach is applied to a case study with real data. The solution exposes the important impact of uncertainty on this problem, especially on the SO _X reduction, while the CO₂ reduction plan seems in this case not affected by uncertainty.     

Optimized selection of vessel air emission controls—moving beyond cost-efficiency

Shipping currently has an unexploited potential for improved energy efficiency and reduced emissions to air. Many existing air emission controls have been proved to be cost-efficient but are still not commonly installed on board vessels. This paper discusses the so-called ‘energy paradox’ in maritime transportation, presenting barriers to overcome and criteria to consider when selecting cost-efficient air emission controls. Current approaches typically select available controls based on their cost-effectiveness. While this is an important aid in the decision-making process, and, in relative terms, easy to quantify, it is not a sufficient criterion to capture the true preferences of the decision-maker. We present in this paper a multi-criteria optimization model for the selection of air emission controls. This decision framework can also incorporate subjective and qualitative factors, and is applied to the shipping company Grieg Shipping. A survey among internal Grieg Shipping stakeholders identifies the important criteria to consider, their relative importance, and the scoring of the controls. This empirical data is used as parameters in the model and the model is then applied on a vessel of the Grieg Shipping fleet. The results show that nonfinancial factors play an important role in the selection of air emission controls in shipping.     

Designing optimal routes in a liner shipping problem

A real liner shipping problem of deciding optimal weekly routes for a given fleet of ships is considered and a solution method for solving the problem is proposed. First, all feasible routes for each ship are generated together with the cost and the duration for each route. The routes are given as input to an integer programming (IP) problem. By solving the IP problem, routes for each ship are selected such that total transportation costs are minimized and the demand at each port is satisfied. The total duration for the routes that are selected for a given ship must not exceed one week.

The real liner shipping problem is solved together with four randomly generated test problems. The computational results show that proposed solution method is suitable for designing optimal routes in several liner shipping problems.     

A simulation study on the design of flexible cargo holds in small-sized bulk ships

A simulation study on the design of flexible cargo holds in small-sized bulk ships is presented. The ships considered are equipped with moveable bulkheads which can be placed in a given number of positions in the cargo hold. In this way the ships' cargo holds can be partitioned into several smaller holds with flexible sizes, and several cargoes can be lifted simultaneously by the same ship. The simulation study deals with designing an optimal cargo hold 'configuration' which gives the best flexibility when cargo quantities vary. The results show that there are significant potential savings by finding an optimal cargo hold configuration.