Weather routing and safe ship handling in the future ...

Ocean Engineering (xxxx) xxxx–xxxx

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Weather routing and safe ship handling in the future of shipping Lokukaluge P. Perera1, C. Guedes Soares

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Centre for Marine Technology and Ocean Engineering (CENTEC), Instituto Superior Tecnico, Universidade de Lisboa, Lisbon, Portugal

A R T I C L E I N F O

A BS T RAC T

Keywords: Weather routing Safe ship handling Ship energy efficiency Speed optimization Emission control

An overview of weather routing and safe ship handling approaches in the future of shipping is presented. Weather routing provides the recommendations on transportation routes prior to and during ship sailing in various navigation constraints under global weather forecasts. Safe ship handling provides the recommendations on vessel position, orientation and speed conditions that should execute at the previously recommended route (with safe navigation conditions) under local weather conditions. Both approaches that complement each other should be implemented simultaneously to achieve optimal and safe ship navigation conditions. That will facilitate towards future navigation tools in integrated bridge systems, where the respective environmental pollution due to the shipping industry should be minimized.

1. Introduction 1.1. Shipping industry The shipping industry is associated with approximately 90% of the world trade (International Chamber of Shipping, 2009) and the shipping volume has doubled over last two decades (Lun et al., 2013). This trade demand in shipping results congested sea routes that contribute to reduce the navigation safety and increase the operating costs. In general, the operating cost of a vessel is mainly influenced by bunker fuel and lubricating oil prices, which consist 50– 60% of the total ship operating cost (World Shipping Council, 2008). When the oil price was at its high level, a considerable reduction in bunker fuel and lubricating oil usage was demanded from the shipping industry by the International Maritime Organization (IMO) and other maritime authorities (IMO, 2012). It is expected that the same approach eventually reduces shipping related environmental pollution including greenhouse gas (GHG) emissions (International Energy Agency, 2010, 2011; Perera and Mo, 2016a, 2016b). 1.2. ECDISs Preplanned ship routing under weather forecast data can play an important role in reducing the total operating costs of vessels (IMO, 1999). Ship routing is a part of modern electronic chart display and information systems (ECDISs) under integrated bridge systems (IBSs) and that facilitate to obtain weather forecasts from various commercial providers (Raytheon Anschutz GmbH, 2012). ECDISs replace conven⁎

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tional paper charts in ship navigation and consist of sophisticated digital display systems to produce comprehensive environment information (i.e. shore information, ship information and, hydrographic information, etc.) (Perera and Guedes Soares, 2015). Those systems are used for not only route planning but also route monitoring situations in ship navigation. In addition, the navigation safety and security features (i.e. traffic separation and lane information, restricted and protected areas, ice areas, fishing ground information) are also incorporated under ECIDSs as an essential part of ship routing. The NavTex message system is also an integrated part of IBSs and transmits urgent marine safety information (i.e. weather forecasts, weather related navigation warnings, search and rescue notices, etc.) among ships and shore based authorities. Vessels receive this information (i.e. the NavTex messages) within approximately 370 km (200 nautical miles) from the shore, and that facilitates a simple, low cost and automated solution to the shipping industry. Hence, NavTex is an important element in shipping to improve the navigation safety and that consists of a collaboration among several maritime institutes: IMO, International Hydrographic Organization (IHO), Worldwide Navigation Warning Service (WWNWS) and Global Maritime Distress Safety System (GMDSS). 1.3. Weather forecast Weather routing (i.e. pre-voyage planning) plays an important role in various transportation systems (Motte et al., 1987; Stratton, 1974; Burnett, 2000; Ng et al., 2009; Prpiæ-Oršiæ et al., 2015; Vettor and Guedes Soares, 2016b). However, there are several external factors that

Corresponding author. E-mail address: [email protected] (C.G. Soares). Present address: The Norwegian Marine Technology Research Institute (MARINTEK), Trondheim 7052, Norway.

http://dx.doi.org/10.1016/j.oceaneng.2016.09.007 Received 16 February 2016; Received in revised form 24 August 2016; Accepted 6 September 2016 0029-8018/ © 2016 Elsevier Ltd. All rights reserved.

Please cite this article as: Perera, L.P., Ocean Engineering (2016), http://dx.doi.org/10.1016/j.oceaneng.2016.09.007


L.P. Perera, C.G. Soares

influence on such weather routing type applications in shipping: prevoyage weather forecast, during-voyage weather, vessel traffic information (Perera et al., 2012c), and navigator's knowledge and experiences. One should note that weather predictions consist of both short-term weather forecasts as well as long-term climate predictions under various environmental data sets. In general, weather forecast consists of predicting the state of the atmosphere for a given location at a shorter period (e.g. 6–16 days), however the prediction accuracy will degrade for the periods larger than 10 days. Global weather predictions are formulated under predefined mathematical models of the atmosphere and meteorological statistical analyses by various meteorological institutes (Cox and Cardone, 2002). Predicted wind conditions are used to derive weather forecasts by analyzing various global mathematical models of wave, wind, ocean and tidal current, ice, atmospheric pressure and temperature conditions. One should note that these mathematical models are used as numerical weather prediction tools to develop the required forecast based on current weather conditions. A selected set of such global weather forecast models with the respective providers can be summarized as: Global Forecast System (GFS) Model, Global Data Assimilation System (GDAS) model (NOAA, 2016), Integrated Forecast System (IFS) model (ECMWF, 2016), and Global Environmental Multiscale (GEM) model (Environment Canada, 2016). In general, climate predictions consists of predicting the state of the atmosphere for a given location at a longer period (e.g. several years). Atmospheric and land (i.e. soil) related variables such as temperatures, winds, precipitation to soil moisture and atmospheric ozone concentration information are considered as data sets for such predictions. Furthermore, the entire earth is represented by various grid resolution points in these climate data sets with various data formats (i.e. GRIB1/ GRIB2: Gridded Binary, netCDF3/netCDF4: Network Common Data Form, HDF4/HDF5: Hierarchical Data Format, HDF4-EOS2/HDF5EOS5: HDF4-Earth Observing System, and GeoTIFF: Georeferenced raster imagery). However, both short-term weather forecasts and longterm climate predictions can complement to each other. A data set of commercial weather forecasts may consist of various weather parameters. e.g. significant wave heights (i.e. combination of wind waves and swell), primary wave mean periods and directions; significant wave heights, peak periods and directions of wind waves; significant wave heights, peak periods and directions of swell; mean speeds and directions of wind; tidal and ocean current speeds and directions; ice conditions and surface temperature. These predicted parameters along with the respective statistical weather data can be used to derive other unknown weather parameters (Tsujimoto and Hinnenthal, 2008). One should note that these weather parameters are derived by global wind maps, as mentioned before. Therefore, the accuracy of weather forecasts can only be improved by high quality wind information and appropriate weather analysis tools. e.g. an initial error of 16% in wind speeds accumulates a final error of 25–30% in predicted wave heights (Gemmill, 1998). Several commercial weather forecast initiatives are implemented and many advanced mathematical models and weather analysis tools are developed in recent years to improve the prediction accuracy. Furthermore, the advancements in radar, satellite, and other weather-sensing technologies as well as powerful supercomputers further improve the weather forecast accuracy.

where appropriate ship speeds and orientations (i.e. heading and course) with respect to local weather conditions should be selected by the navigators. Ship navigators use various safe ship handling techniques with respect to their experiences in avoiding rough weather conditions (Vettor and Guedes Soares, 2016a, 2016d). Such safe ship handling techniques improve the safety and stability conditions of vessels by avoiding slamming, propeller racing and ventilation, excessive acceleration, and dangerous hull stress and fatigue levels (i.e. green water effects). Furthermore, the same techniques minimize the effects of seasickness and other health related conditions of the crew. Similarly, safe ship handling can increase the quality of goods that are transporting, the safety of on-board machinery operations and the comfort of the passengers in the vessel. It is believed that safe ship handling should play a supporting role in weather routing. Furthermore, various ship operations (i.e. ship-toship, rescue and recover, drilling and dredging, and helicopter landing, etc.) can also be benefited from both weather routing and safe ship handling to improve the operational safety. The implementation steps and respective challenges in weather routing and safe ship handling with respect to the shipping industry are further described in the following sections. 2. Navigation parameters 2.1. Ship resistance Ship performance (i.e. seakeeping and maneuvering) degrades under various weather factors (i.e. wave, wind, tide and current conditions) due to hull resistance and undesirable vessel motions. In general, ship resistance consists of four main components: frictional resistance, residual resistance, added wave resistance and wind resistance. Frictional and residual resistance relates to the under-water section and air resistance relates to the over-water section of the ship. In general, frictional resistance consists of 70–90% and 40% of the total resistance in low-speed and high-speed ships (MAN Diesel and Turbo, 2012), respectively. Frictional resistance depends mainly on ship speed, hull underwater volume and surface conditions (i.e. fouling, corrosion and the coating of paint). Frictional resistance is optimized during the ship design phase by calculating proper hull shapes and surface conditions. However, these optimal conditions can degrade at the ship operation phase, where vessel speed reduces significantly (Woods Hole Oceanographic Institution, 1952) due to increased ship resistance. Residual resistance contributes 8–25% and 40–60% of the total resistance in low-speed and high-speed ships (MAN Diesel and Turbo, 2012), respectively. Residual resistance (i.e. pressure distribution on the ship surface) depends on the pressure profile (i.e. the water flow profile and flow separation conditions) around the vessel. This pressure profile is the major source of wave making resistance calculated under ship maneuvering conditions. Similarly, residual resistance is optimized during the ship design phase by designing proper hull shapes and surface conditions. In general, the combination of ship frictional and residual resistance is considered as calm water resistance and that should also be reduced to improve ship performance. That can be done by selecting appropriate vessel speeds in ship navigation. Vessels experience additional ship resistance due to ocean waves. This added resistance due to encounter waves introduces various forces on the vessel hull (Matulja et al., 2011): the drifting force due to incident waves and the waves generated by heaving and pitching, the damping force due to heaving and pitching, and the diffraction force due to the interactions between the vessel and the encountering waves. These forces are also influenced by ship speeds and the respective sea conditions (i.e. wave height, wave angle and length/period), where prominent waves from the fore can affect added ship resistance, significantly. Furthermore, the encounter wave period also influences

1.4. Ship navigation Ship navigators use global weather forecasts to plan ship routes and that approach can be categorized as weather routing (Vettor and Guedes Soares, 2015a, 2015b, 2016b). However, actual weather can differ from predicted conditions during the voyage. The navigators should be equipped with safe ship handling tools, techniques and experiences to overcome such situations. Hence, safe ship handling is also illustrated as an important part of weather routing in this study, 2



sea surface temperature may relate to ocean and tidal currents, therefore that can further increase ship resistance. However, the information on sea surface temperature and ice conditions is used relatively less in ship navigation situations with compared to other parameters. These weather factors influence ship resistance significantly and degrade vessel speeds. Ship performance in such situations often measures under speed of advance (SOA) and that can be categorized as the speed that the vessel can achieve at a given shaft rotation (i.e. propeller speed) without external forces. Rough ocean conditions reduce SOA and also lead to dangerous ship navigation situations (i.e. lost maneuverability and unstable steering) (Perera and Guedes Soares, 2012b). e.g. a Virginia class cruiser is capable of 25 knots in calm water conditions may reduce 10–17 knots in sea state 7 (Kehoe et al., 1983). Therefore, the main objective in weather routing and safe ship handling approaches is to minimize such weather related effects in ship navigation.

added ship resistance and uses to calculate ship speed losses under seakeeping conditions (IMO, 2007). i.e. maximum added ship resistance (i.e. non-dimensional) due to regular encounter waves is observed around an equal ship and wave length situations in head seas (Matulja et al., 2011). Vessels also experience various undesirable motions due to encounter waves and that reduce vessel propulsive efficiency. Hence, wave conditions around vessels should be considered for weather routing and safe ship handling approaches, where the respective wave effects should be minimized (Perera et al., 2015a). Wind resistance contributes 2–10% of the total ship resistance (MAN Diesel and Turbo, 2012) and relates to vessel speeds, superstructure shapes and areas, and encounter wind speeds and directions. Wind resistance is also considered under weather routing and safe ship handling approaches, where the respective wind effects on ship navigation should be minimized. A general discussion on ship resistance is presented above. A simplified ship resistance structure should be implemented in weather routing type applications to reduce the respective computational complexities. It is also believed that optimizing ship routes with respect to main ship resistance components can also minimize other undesirable ship motions. Ship resistance discussed above also depends on vessel loading conditions because under-water and over-water sections relate to forward and aft drafts. Hence, ship resistance is also calculated with respect to various loading conditions (i.e. laden and ballast conditions) in weather routing type applications. In general, full and model scale experiments and numerical models/techniques are used to estimate such ship resistance values, initially. In full scale experiments, sea trials under various weather conditions (i.e. calm and rough sea conditions) are conducted (ISO19019, 2005) to verify such results. In a model scale experiment, geosim models of the respective vessels are tested under towing tank conditions and the test results can also extrapolate into full scale vessels. These numerical models/techniques are derived under physical laws and their seakeeping and maneuvering capabilities are estimated under various ocean wave spectra, where the same results are also extrapolated into full scale vessels.

2.3. Sea trials Weather effects on vessels are often identified realistically in sea trials. Wind and wave conditions are the primary factors that influence on ship speed variations as mentioned before. Head wind and wave conditions reduce ship speed and following wind and wave conditions may improve ship speed slightly in some navigation situations (i.e. wind and waves can provide supporting forces). In general, high wind and wave conditions reduce the propeller thrust and increase the drag from steering corrections of the vessel. Therefore, wave and wind forecasts along the voyage are an essential part in predicting accurate ship speeds and vessel motions (i.e. heave, pitch and roll). Various relationships among ship resistance, speed and power are presented in the recent studies to predict vessel performance. Ship performance is also evaluated by removing wave and wind effects with various numerical techniques, where the respective speed-power plots in calm water conditions are derived. These relationships (i.e. vessel speed, engine power and ship resistance) are developed primary by ship designers under computational simulations. The same results are verified under model experiments and actual sea trails. Those sea trials often consist of measuring ship speed-power performance under various wave and wind conditions that are conducted under various guidance, adopted recommendations and standards developed by IMO and other classification societies (ITTC, 2005a; MARIN, 2006; ISO15016, 2002). Model tests and sea trials are often conducted under calm water conditions as maneuvering tests, where the required ship power/thrust for selected ship speeds (i.e. SOA) are calculated. On the other hand, the same experiment results can be extrapolated into rough weather situations, where vessel speed reductions are expected due to ship resistance, engine loading and propulsion efficiency variations. Ship navigation under considerable wind and wave conditions are identified as seakeeping, where various interactions among ship speed-power, vessel motions and weather conditions can be observed. Ship performance and navigation data under various weather conditions are collected by onboard sensors and data acquisition systems to observe actual sea keeping capabilities of vessels in such situations. However, there are many challenges that are observed in such data (Flikkema, 2009). e.g. the data scattering effects due to rough weather conditions. Therefore, it is expected that the weather routing and safe ship handling approaches can minimize these weather related interactions, where the quality of ship performance and navigation data can also be improved.

2.2. Other environmental factors Other environmental factors on ship navigation can be categorized as: ocean and tidal currents, fog, surface temperature and ice conditions. Even though ocean and tidal currents move slowly with respect to wind and wave conditions and that can have a considerable impact on average speeds and heading conditions of vessels. Furthermore, the interactions among wave, wind, ocean and tidal current conditions can create complex ship navigation situations, e.g. following ocean currents in a wave surface can increase wave lengths, decrease wave heights and break waves, and vice versa. Therefore, vessels can experience undesirable ship motions in such situations and degrade their speeds, significantly. Fog conditions create visibility problems in ship navigation and also reduce vessel speeds. These low visibility conditions also contribute towards many ship collision and near collision situations (van Manen and Frandsen, 1998; Perera et al., 2011, 2012a). Sea surface temperature and ice conditions are other weather factors that influence ship navigation, significantly in the arctic type regions. Low surface temperature creates ice crystals on seawater and contributes towards additional ship resistance and dangerous navigation situations, where the navigation safety (i.e. ice breaking) in vessels should be prioritized (ABS, 2009). Such ice conditions can be dangerous to vessels due to their thickness that is categorized into two types (Bowditch, 2002): floating ice and deck ice. In general, net ice resistance relates to ship speed (ITTC, 2002) and the respective forces can challenge hull strength and fatigue limits of the vessel. While vessels are navigating in low surface temperature conditions, possible encounters with sea ice should be avoided (i.e. dangerous collision situations). Furthermore,

2.4. Response amplitude operator Seakeeping conditions in vessels are studied under their responses with respect to regular and irregular waves. Irregular waves consist of 3



undesirable vessel motions by selecting calm weather conditions, where the respective vessel performance can be optimized. Hence, weather routing selects optimal navigation routes for vessels under global weather forecasts (Hinnenthal, 2008). That is also categorized as optimizing (i.e. minimizing) ship resistance (i.e. frictional, residual, added wave and air resistance) in vessels, where ship performance models are compared against weather forecasts to extract vessel responses along the respective voyages (i.e. in several days). In general, added wave and air resistance is optimized for a majority of weather routing type applications. One should note that appropriate ship speeds should be selected under weather routing, where calm water ship resistance (i.e. frictional are residual resistance) that relates to ship speeds is minimized. Weather routing associates with various optimization algorithms (Vettor and Guedes Soares, 2015c; Simonsen et al., 2015). These optimization algorithms are executed under global weather forecasts between departure and arrival ports with respect to vessel characteristics and motions limitations. Ocean waves are the most important factors in weather forecasts that influence ship motions, significantly. Hence, wave forecast (i.e. significant wave height, peak period and encounter angle) is used extensively in these optimization algorithms. The weather forecast parameters (e.g. wave height) are non-stationary (changing with time), therefore that can introduce additional challenges in such optimization algorithms. Similarly, other weather factors (i.e. wind, ocean and tidal currents, ice conditions and surface temperature) are also considered in such optimization algorithms. Various ship characteristics are also incorporated into these optimization algorithms (Bowditch, 2002) such as ship hull types, speed capabilities, safety considerations, cargo and loading conditions with sea trail and model experiment data (i.e. power–speed, speed–wave and speed–wind conditions). The features in weather routing can be divided into two categories of route and speed optimization. Route optimization selects the waypoints with respect to weather forecast and speed optimization derives the best possible vessel speed in each route segment (i.e. between two waypoints) with respect to available/appropriate engine power and propulsion configurations. Furthermore, weather routing may consist of additional optimization goals such as travel time, fuel consumption, and total distance in each ship route. Therefore, weather routing often consists of multi-objective optimization approaches (Szlapczynska, 2015) to include the required parameters, constrains and optimization goals. However, these multi-objective optimization approaches require not only more sophisticated tools but also appropriate mathematical models to overcome the present challenges.

several wave heights, encounter periods and angles with respect to ship heading and course conditions. Therefore, vessels can encounter undesirable ship motions under such weather (i.e rough weather) conditions and that may not be able to reduce by rudder and propulsion control systems. Furthermore, ship dynamics are often categorized as an under-actuated system, which has inadequate rudder and propeller actuations to execute appropriate maneuvers. Lost maneuverability and capsizing situations under rough weather conditions (Perera and Guedes Soares, 2012a, 2012b) can result in such under-actuated vessels. To avoid these types of dangerous navigation situations, ship motions with response amplitude operators (RAOs) under various wave groups are studied. RAOs help to evaluate vessel motions at the ship design phase, where ship responses under operational speeds and expected sea states can be simulated. Therefore, likely vessel behavior at various wave groups (i.e. significant wave height, encounter periods and angles) can be identified and appropriate design modifications and operational limitations to avoid rolling, capsizing and other dangerous situations can also be introduced. Furthermore, various safety constrains (i.e. rolling, capsizing and other dangerous conditions) on vessels can also be identified at this step and that information can be emphasized on ship operational manuals. Ship RAOs are derived under various mathematical theories and computational techniques (i.e. strip theory methods, panel methods and various computational fluid dynamics codes). One should note that same methods can also be a part of ship resistance calculations. Even though RAO calculations are based on strip theory based methods (Salvesen et al., 1970), panel methods with three dimensional flow around vessel hulls are also presented in the literature (Kohlmoos et al., 2001). Non-linear damping coefficients in ship motions are also incorporated in these calculations to improve the accuracy (Adgeest, 2008) and the results are verified through model scale experiments under various seakeeping conditions (Payne et al., 2005). 2.5. Ship power Ship resistance and undesirable vessel motions contribute towards excessive power requirements with high bunker fuel consumption. In general, bunker fuel consumption in a vessel can be approximated to the third power of its navigation speed (Tsujimoto et al., 2008) and additional power losses due to undesirable ship motions should also be considered in these calculations. It is expected that average ship speeds in vessels will be reduced in the future, considerably. Slow vessel speed and low motion conditions reduce ship power requirements, therefore more cargo can be transported (Magirou et al., 1992) in vessels. However, slow ship speeds can increase voyage durations and introduce additional navigation costs (i.e. charter and storage charges). Therefore, these interactions among ship resistance, vessel motions, cargo handling, engine-propulsion configurations, weather conditions, and appropriate voyage durations (i.e. voyage time) should be considered to improve vessel performance. These interactions are considered under two main sections, weather routing and safe ship handling, in this study as the main contribution.

3.2. Route planning A ship route consists of several way-points, which should be followed by the vessel either in manual (i.e. the navigator) or autopilot modes under Electronic Chart Display Systems (ECDISs). ECDISs is an essential part of modern integrated bridge systems (IBS) that support weather routing type applications. These waypoints in ECDISs create several voyage legs and each voyage leg consists of respective speed or/ and engine power profiles. These profiles should be followed by the vessel to achieve the required estimated time of departure (ETD) and estimated time of arrival (ETA) conditions among the respective ports. It is recommended to follow an engine/power profile rather than a ship speed profile during weather routing to improve vessel energy efficiency. It is well known that marine engines are operated around several operating points (i.e. operating modes) and that information can be used in weather routing, which creates an engine/power profile along the voyage. In general, vessels are often following fuel consumption requirements due to the respective charter restrictions in ship navigation. Therefore, such fuel consumption requirements should also be included under the respective optimization algorithms in weather routing.

3. Weather routing 3.1. Routing parameters Vehicular routing under various navigation constraints (i.e. weather, traffic, distance, and transport costs) is studied by many researchers (Eksioglua et al., 1997). Weather routing is one of the vehicular routing problems, which is extensively considered by the shipping industry (Laporte and Osman, 1995) to improve vessel energy efficiency. Weather routing provides the route recommendations on ship navigation prior to and during voyages under global weather forecasts. The main objective in weather routing is to minimize ship resistance and 4



to evaluate the success in weather routing. A Pareto optimal control approach based on hydrodynamic characteristics of a vessel for weather routing is proposed in Harries and Hinnenthal (2003). A modified isochrones method with an evolutionary approach for weather routing to improve the navigation safety in a vessel is proposed by Szlapczynska and Smierzchalski (2007). Furthermore, various weather routing approaches for ship navigation under computational intelligence, neural networks (Palenzuela et al., 2010.) fuzzy logic (Pipchenko, 2011) and genetic algorithms (Vettor and Guedes Soares, 2016c), are presented in the respective studies. A weather routing approach for a vessel under degraded navigation conditions is proposed by Bottner (2007). A weather adaptive navigation system based on Lagrange multiplier method is presented by Tsujimoto and Tanizawa (2006). An optimal track selection method based on Dijkstra's algorithm for a naval vessel under various wind and sea conditions is presented in (Montes, 2005). However, these optimization algorithms limit to a selected set of ship navigation parameters and extensively relate to the accuracy of weather forecasts. Weather routing capabilities to overcome such challenges under actual weather conditions that vary from the forecast have not properly considered in these approaches.

In general, weather routing is recommended for long voyages (i.e. 1500 miles or more in unrestricted navigation waters) (Bowditch, 2002). However, the same limitation is also influenced by the following conditions: the grid size of weather forecast, land mask size of digital maps and step size of optimization algorithms. Furthermore, that also depends on the accuracy of weather prediction models. e.g. the wave prediction models in coastal waters are less accurate than ocean waters (Rathje et al., 2003). Coastal weather information is available only in some small navigation areas under comprehensive environmental monitoring sensors and systems. Therefore, local weather forecasts may have a high prediction accuracy in some situations. Due to the improvements in weather prediction technology, short voyages with local weather forecasts are also planned and that is categorized as “weather routing in coastal navigation” (Tsujimoto et al., 2008; Vettor et al., 2016). Short voyages associated with rescue and recovery operations with high safety and security constrains under rough weather conditions are also benefited from such weather routing type applications (Davidson, 2009). Global and local weather forecasts can be used appropriately to avoid potential hazard conditions (i.e. abnormal waves, tropical cyclones, storms and icebergs) in such ship navigation situations. The success in weather routing is evaluated by comparing the proposed ship routes with the shortest distance route (i.e. between the respective ports) under the respective navigation requirements and ship performance levels. Several commercial weather routing applications are developed in the recent years to satisfy such navigation requirements and ship performance levels and implemented as both shore based and onboard systems. Shore based systems behave as advisory services to vessels and inform future rough weather situations through various offshore centers. These centers consist of experienced meteorologists, who can inform and guide vessels to avoid rough weather situations. However, shore based weather routing systems can face various challenges, where ship navigators may need continuous advisory services under rough weather conditions (Stoter, 1992). Furthermore, various communication difficulties and cost constraints for transmitting large data sets among ships and advisory services make shore based systems less attractive in weather routing. Vessels are also guided by onboard weather routing systems that have additional flexibilities to review more alternative vessel routes. Inadequate experimental results are published in such commercial weather routing systems to the authors’ knowledge, therefore the success in those systems cannot be summarized. Weather routing is still a subject area for future researchers due to the same reasons.

3.4. Maritime rules and regulations Weather routing reduces the overall operating costs of vessels by selecting optimal ship routes to minimize bunker fuel consumption. Fuel consumption due to the transport sectors contributes to environmental pollution, including greenhouse gas (GHG) emissions (Martin and Shaheen, 2011). The International Maritime Organization (IMO) has stabilized the Marine Environmental Protection Committee (MEPC) in 1973 to address such marine pollution issues. Furthermore, the International Convention for the Prevention of Pollution from Ships (MARPOL) was adopted by IMO in 1973. A new chapter to MARPOL Annex VI was adopted in 2011 to prevent GHG emissions due to the shipping industry. Several ship energy efficiency measures to reduce GHG emissions were introduced as a part of the MARPOL Annex VI (Bazari and Longva, 2011). Therefore, these measures have influenced to improve ship energy efficiency by adopting new technological advancements for both existing and future vessels. The most important energy efficiency measures under the same can be summarized as: Energy Efficiency Design Index (EEDI) for new ships and Energy Efficiency Operational Indicator (EEOI) and Ship Energy Efficiency Management Plan (SEEMP) for all ships. EEDI consists of a relationship between the benefits and environmental impact due to the shipping industry as an expression of the CO2 emission per tonne–mile. That should be considered during the design phase of new vessels. EEOI consists of energy efficiency in the form of CO2 emissions per unit of transport work and indicates the fleet performance with regard to CO2 emissions. One should note that this voluntary measure is applicable for all ships that perform transport work. SEEMP consists of an appropriate energy management plan for vessels to improve their performance. This mandatory mechanism enforces the international shipping industry to optimize its operational conditions and implement new energy efficient technologies to vessels. Weather routing and speed optimization as two feasible approaches to improve ship energy efficiency are identified under the SEEMP. The recommendations on the mandatory regulations of ship routing/safety systems are requested from the member states in IMO (2003). e.g. that prohibits placing voyage and convergence junctions on ship routes, where various vessel crossing situations (i.e. vessel traffic) are expected. Furthermore, drilling rigs, exploration platforms and other offshore structures should not locate in the vicinity of the respective ship routes under the same. These navigation constrains can play an important role in weather routing and should incorporate with ECDISs (IMO, 1995b; 2006). Hence, various rules, regulations, guidelines and recommendations relate to ship routing should also be

3.3. Recent studies The early steps in weather routing were established around 1855, by Maury, with the least-time track approach for sailing vessels. These vessel routes were based on historical wind and current data compiled from ship logs. A similar approach for calculating a least-time track for ships was introduced by James around 1957 (Bijlsma, 1975). In general, weather routing algorithms are implemented under various ship navigation constraints with respect to space and time variations and global and local weather forecasts. The respective navigation parameters are optimized under deterministic or stochastic conditions (Azaron and Kianfar, 2003) in such algorithms. However, the uncertainties in weather forecasts and navigation parameters can introduce additional challenges in these algorithms. These weather routing algorithms can be categorized into two main divisions of network and calculus of variations (i.e. optimal control theories) approaches (Bijlsma, 1975). An optimal control approach for ship routing under a least-time track is presented by Bijlsma (1975). Similarly, ship routing as a minimum time problem is presented by Ishii et al. (2010). One should note that the respective fuel consumption in the minimal-time route can be compared with other ocean crossing situations (Bijlsma, 2008) 5



4. Safe ship handling

considered at the implementation step of weather routing. It is also believed that the respective maritime authorities may further enforce these mandatory rules and regulations in the future and that may challenge the sustainability of the shipping industry. Therefore, shipping companies should adapt appropriate measures to adopt same rules and regulations under weather routing.

4.1. Local weather Safe ship handling provides the recommendations (i.e. ship heading, course and speed) on ocean going vessels to achieve safe navigation conditions under local weather conditions. Ship optimal positioning (i.e. ship orientation and speed) under actual weather conditions is considered in such situations. In general, a global optimization based weather routing approach may create inappropriate solutions for a vessel, where various undesirable vessel motions (i.e. heavy rolling or pitching) (Bijlsma, 2004) can be encountered. Hence, such situations can be compensated by safe ship handling. Even a vessel in an optimal route (i.e. under weather routing) can face dangerous rolling and/or parametric rolling conditions in some situations. e.g. weather routing considers the average values of predicted significant wave heights, encounter wave lengths and directions, therefore if the ship length and wave length are in an equal situation with an inappropriate encounter angle that can create such dangerous situations. To overcome such situations, safe ship handling should be executed by fine-tuning of the vessel orientation on the route under local weather conditions to improve the navigation safety.

3.5. Current challenges Additional industrial challenges with respect to weather routing are summarized in this section. Weather forecasting is a predicted state of the atmosphere for a selected location at a given time period. That is created by several mathematical models as described previously, therefore some weather prediction errors are also expected. Actual weather conditions can differ from the forecast, therefore unexpected vessel navigation and motion conditions can be encountered in the recommended ship routes. To overcome such situations, statistical weather data along the respective ship routes are considered to correct such erroneous weather information in some situations. Furthermore, these statistical data can also be used to predict ship speeds under the respective weather conditions and that is another advantage in this approach. Ship routes often associate with unexpected weather conditions. Rough weather conditions developed faraway from the routes can influence (i.e. large wave heights) on ocean going vessels. The navigator should respond appropriately to avoid such rough weather conditions by monitoring the progress of the voyage and the future weather conditions. On the other hand, vessels can encounter unexpected weather conditions due to ship speed limitations. e.g. when a vessel is expected to navigate before or after a storm, it can end-up in the center of the same storm due to inadequate or unexpected speed variations. Such situations can introduce additional challenges in weather routing with respect to predicted ship speeds (i.e. ship speed as a function of significant wave height, encounter frequency and direction and engine power configurations). Weather routing provides the recommendations on transportation routes prior to and during ship sailing under various navigation constraints under global weather forecasts. Such routes consist a group of navigation points (i.e. waypoint) that should execute under ECDISs. ECDISs are associated with various ship autopilot systems that guide vessels to follow (i.e. the vicinity of waypoints) the recommended ship routes. Adequate ship speeds should be executed in each voyage leg by the navigator in such situations to satisfy the route optimality. However, vessels may not be able to follow the waypoints (i.e. optimal routes) assigned by weather routing due to inadequate ship speeds in some situations. The actual navigation path of a vessel can also vary along the route due to weather effects. A vessel may deviate from the proposed optimal route in such situations, where several other possible actions can be considered: the vessel should navigate towards the optimal ship route, next proposed waypoint or another optimal ship route should be calculated from the present ship position with new weather forecast. Furthermore, vessels often face various safety considerations in such unexpected weather conditions. Even an experienced navigator can make wrong decisions due to such situation complexities in ship navigation. The navigator's ship handling knowledge and experiences can play a valuable role in such situations. On the other hand, the navigator's inexperience or inadequate knowledge can introduce a considerable risk on the vessel safety under similar navigation situations. Therefore, safe ship handling under rough weather conditions is proposed and decision support features on IBSs (Perera et al., 2012a, 2012b) to overcome such navigation challenges are also presented in the following sections.

4.2. Decisions support systems Safe ship handling approaches are practiced by ship navigators with individual knowledge and experiences throughout the maritime history. Even an experienced navigator can make inadequate decisions (i.e. human errors) resulting in maritime accidents and causalities (Rothblum et al., 2002). To overcome such navigation challenges in shipping, several onboard advisory mechanisms to practice safe ship handling, so called”Decision Support Systems”, have also been proposed (Adgeest, 2008; Perera et al., 2012d; Rodrigues et al., 2012; Lajic et al., 2010). Ship stability calculations with vessel loading information can also be a part of such decisions support systems. These advisory systems interact with actual ocean wave, wind, current and tidal conditions to propose appropriate vessel orientations under local weather conditions. That consist of selecting appropriate ship course, heading and speed values with respect to actual weather conditions, where navigators can make appropriate safe ship handling decisions with the respective information. Such advisory systems in safe ship handling consist of various onboard monitoring features and that can be categorized under three groups: wave condition monitoring, motion monitoring, and stress monitoring. However, various combinations of these categories are also developed in the shipping industry and an overview of such applications is presented in the following sections. 4.3. Wave condition monitoring Wave interactions around vessel hulls degrade ship performance, reduce propulsion efficiency and increase drag from steering corrections. These wave-hull interactions also increase wave making and added resistance, as mentioned before. Added resistance due to waves is largely influenced by wave heights, lengths and encounter angles and that information is also used for ship speed predictions. Ship speed and motion predictions are done by considering the wave directional spectrum around the hull. Therefore, the main objective of wave condition monitoring is to evaluate the wave spectra around the ship hull under current weather conditions. That can be done under wave height measurements or wave radar sensors by observing the wave parameters with respect to the ship position and orientation. The wave and vessel related parameters measured and estimated by such sensors and systems can be summarized as: ship displacement, relative wave height, actual wave height, significant wave height, average wave period, wave mean direction and peak wave period. These sensors are associated with various digital signal processing units and estima6



4.5. Stress monitoring

tion algorithms to improve the measurement accuracy (Pascoal et al., 2007). Hence, such systems can provide comprehensive overviews of wave spectra around vessels and that can verify weather forecasts. The wave spectra around ship hulls are used to determine appropriate ship orientations (i.e. heading and course), where undesirable ship motions and dangerous hull conditions can be avoided (Pascoal and Guedes Soares, 2009). Wave height information measured by wave height measurement sensors is inadequate to estimate the respective ocean wave spectra around vessels. In general, the wave spectra around vessels are estimated by considering other ship related information such as RAOs and vessel motion measurements (Pascoal et al., 2007). Wave radar systems may consist of several remote sensing applications that collect direct or indirect wave spectrum information around vessels. However, specular reflections of the sea surface around vessels are also observed by these sensors in some situations. These sensors should be mounted on upper deck positions of vessels and estimate essential wave field parameters such as two-dimensional frequency wavenumber spectrums, significant wave heights, peak wave periods and directions, and ocean current speeds and directions in real-time. Some wave radar systems can recognize multiple wave groups of swell and wind waves, where swell waves propagate faster than wind waves (Gurgel and Essen, 2000). Wave spectra and ship RAO information are used to simulate ship motions under various vessel orientations in these decision support systems. Dangerous ship navigation situations can be identified by such simulations and that can create safety advices to improve vessel stability and reduce undesirable vessel motions. One should note that the respective vessel loading conditions can also play an important role in these RAO calculations. Hence, RAO calculations are often conducted under various loading conditions and used to estimate vessel motions. Those calculations are often done by onboard dynamic calculations, otherwise information databases to predict ship motions accurately under various ship orientations in weather conditions are provided. RAO information from the respective databases is extrapolated to calculate the actual transfer functions with respect to the current loading conditions of vessels. Therefore, that step further improves the accuracy of predicted ship motions. Dangerous ship motions and capsizing situations can be identified ahead of time by current wave spectra with RAO information, where the navigators may have enough time to respond. Such decision support systems guide the navigators to take appropriate speed, course and heading conditions to minimize undesirable ship motions and improve ship stability.

Undesirable ship motions under different loading conditions generate various hull stresses in vessels. Therefore, cargo loading and fatigue conditions in vessel hulls under rough weather conditions should be observed to identify such dangerous ship navigation situations. That has done by estimating wave induced dynamic loads in ship structures and cargo supporting equipment under rough weather conditions. These estimated structural forces help to make appropriate navigation decisions to save the structural integrity of vessel hulls and cargo supporting equipment. In general, possible ship structural failures can be identified ahead of time in such calculations. Hence, dangerous ship structural failures and/or capsizing situations can be avoided by executing suitable actions by the navigators. The observations of hull stresses and fatigue conditions are an important part of the ship safety and done by strain gauge sensors that are placed various sections of vessels (Perera et al., 2012d). These sensors measure ship bending moments and shear stresses with additional accelerometers on the hull to observe ship motions in the same time. Appropriate mathematical models of vessel structures are used in such situations to calculate bending moments, shear stresses, slamming loads and strength assessments by considering the same measurements. 4.6. Dangerous navigation Ship stability is analyzed at the vessel design phase, where the required distance between the center of gravity and the metacenter, so called”metacentric height”, is calculated. A smaller metacentric height creates a smaller restoring moment, therefore ship rolling motions have a longer rolling period. However, a larger metacentric height creates a larger restoring moment, therefore ship rolling motions can have a shorter rolling period. The excessive stability in a ship makes uncomfortable navigation conditions for the passengers. The metacentric height has a direct relationship with the ship's rolling period, therefore the ship stability should be compromised with the rolling effects (i.e. passenger comfort) in such situations. Ship stability in vessels is challenged by various wave and wind conditions as discussed, previously. If the wave encounter frequencies are near vessel natural frequencies of roll and pitch motions, that excite undesirable ship motions and may create dangerous capsizing situations. However, these situations can be avoided by changing the ship speed, which also changes the wave encounter period. Furthermore, the change in ship heading also has the same effects on such navigation situations. Therefore, appropriate ship speed and orientation changes with respect to the wave spectra around the vessel can play an effective role in safe ship handling. These safety considerations should be accommodated into IBSs to inform similar dangerous situations and execute appropriate actions by the navigators (Perera et al., 2012d). Various ship stability guidelines are established by IMO and other classification societies to avoid similar dangerous navigation situations under rough weather conditions. A selected number of dangerous ship navigation situations (IMO, 1995a, 1995b, 2007) under rough weather conditions are considered and that can be summarized as: surf-riding, broaching, intact stability, synchronous roll motions, parametric roll motions, operability, motion sickness and dangerous loading conditions.

4.4. Motion monitoring Undesirable ship motions are categorized under various indexes with respect to the data that are collected by various motions sensors. The same motion indexes are used as key performance indicators (KPIs) for vessel performance monitoring systems. The main objective of motion monitoring is to evaluate vessel responses under regular and irregular wave conditions by measuring various ship navigation parameters: vessel positions (i.e. GPS), angles (i.e. angles of heading, roll, and pitch), angular rates (i.e. angular velocities of heading, roll, and pitch), and accelerations (i.e. linear accelerations of surge, sway and heave). Furthermore, vessel velocity (i.e. surge, sway and heave), speed and course variations are also estimated from the above measurements. These measurements are based on the following sensors: accelerometers, angular rate sensors, gyroscopes, inclinometers, inertial measurement units (IMUs) and GPS units. Accelerometers measure surge, sway, and heave accelerations, angular rate sensors measure yaw rate, inclinometers measure roll and pitch angles and gyroscopes measure ship heading of the vessel. Various combinations of the above sensors are also available under modern IMUs (Perera et al., 2012b, 2014). The same sensor data are used to compare actual and predicted ship motions along ship routes under varying weather conditions, where the success in weather routing can be evaluated.

4.6.1. Surf-riding Ship navigation under a steep forefront of following and quartering high waves is considered in this situation. The vessel can accelerate in the wave surface and eventually lose its maneuverability. Therefore, that is identified as a dangerous situation in ship navigation. 4.6.2. Broaching Ship navigation under sudden vessel heading variations with 7



heights and periods with the following factors (ITTC, 2006): the degree of fluctuations of roll restoring (i.e. wave passage dependent) and roll damping (i.e. ship speed dependent). Ship parametric rolling can start under a specific ship speed and continue for a specific speed range (France et al., 2001). This range, suitable for parametric rolling, can also act as a speed trap for some ship navigation situations. Involuntary ship speed reductions due to rough weather conditions can further devastate such navigation situations. Ship navigation situations with parametric roll resonance on container carriers is presented (ABS, 2004) and early detection approaches are presented in (Galeazzi et al., 2012). Wave spectra information and appropriate navigation actions can be used to avoid such parametric rolling situations (i.e. by changing ship speed and/or heading to beam sea and slowly coming back to the original heading). Vessels often reach surf-riding and broaching conditions, when the phase velocity of ocean waves is approximately equal to the ship speed component on the wave direction. Furthermore, large surging motions in vessels can also be encountered in such situations, where reduced intact stability conditions are expected. In general, vessels can experience intact stability, synchronous rolling, parametric rolling or any combination of the same situations, when the group velocity of encounter waves is approximately equal to the ship speed component on the wave direction (IMO, 1995a).

unexpected large heeling in a steep forefront of following and quartering high waves is considered in this situation. Similarly, the vessel can lose its maneuverability and eventually capsize. Therefore, that is also identified as a dangerous situation in ship navigation. 4.6.3. Intact stability Ship stability is often calculated under a righting arm curve (i.e. the curve of static stability) (Naval Damage Control Training Center, 1945). This representation is also verified by various dynamic stability conditions of the vessel under various weather and sea conditions (Brown and Deybach, 1998). When a ship is positioned on a crest of following and quartering high waves with the wave length to ship length ratio from 1.0 to 1.5 (ITTC, 2005b), then the vessel can substantially lose its stability and maneuverability on the wave surface. Furthermore, the variations in the center of gravity and buoyancy due to the cargo distribution can complicate such navigation situations. These situations are identified under ship stability calculations and categorized as another dangerous condition for ship navigation. 4.6.4. Damaged stability A damaged hull with flooding in a vessel generates a complex stability situation at the sea (ITTC, 2005d). To overcome such damaged stability situations, ballast water tank systems are often used by ship navigators to control the vessel stability. However, the same can create additional operational challenges, where advanced ballast water control and treatment systems should also be available onboard vessels. Furthermore, various sensors to monitor flooding conditions and read accurate draught values of fore, mid-ship and aft should also be available in such vessels. These dangerous ship stability situations are identified by the respective senor data with the wave spectra information that can also be used to predict possible vessel behavior under damaged stability conditions.

4.6.7. Ship operability Ship operability represents the required conditions of vessel operations that should satisfy to achieve a specific mission at a given sea state without exceeding its predefined motions limitations. That consists of various ship motion limitations of roll, pitch and acceleration conditions (Aasen and Hays, 2010). These motion limits can also be associated with seasickness and other health related conditions of the passengers (Stevens and Parsons, 2002). Therefore, vessels should navigate within these operability limits to avoid health related issues of the passengers.

4.6.5. Synchronous roll Ship navigation in oblique waves, where the vessel natural rolling period coincides with the encounter wave period, can encounter large rolling motions. These large ship rolling motions are most likely to occur in a group of influential stochastic waves. These conditions can lead to inadequate maneuverability and capsizing situations of vessels. Furthermore, rolling motions of vessels are influenced not only by the wave height but also the wave steepness (Froude, 1861), where shorter ocean waves may be steeper than long ocean waves, and such vessel motions further contribute towards parametric rolling situations (France et al., 2001). Therefore, such conditions are identified as another dangerous situation for ship navigation. Several active control approaches to overcome synchronous roll motions in vessels are presented in the literature: fins (Ikeda et al., 1993), moving weights (Treakle III et al., 2000), active anti-roll tanks (Hsueh and Lee, 1997), rudder actuations (Nejim, 2000), bilge keel (Moaleji and Greig, 2007) and passive anti-roll tanks (Tuan et al., 2008). A slight deviation in ship speed and/or heading can change the encounter wave period, where synchronous roll motions in vessels can be avoided.

4.6.8. Motion sickness Humans encounter such motion sicknesses (i.e. seasickness) due to unadaptable or unfamiliar motions. In general, these conditions often occur due to vessel vertical accelerations under roll and pitch motions. Critical motion sickness conditions are categorized as ship motion induced interruptions, where roll or pitch motions are considerably large for the passengers (i.e. to slide or lose balance) (Stevens and Parsons, 2002). Motion sickness can reduce the work efficiency and increase the respective human injuries and fatalities on the ship deck. Therefore, a motion sickness index is introduced (IMO, 1995a, 2007) to quantify such dangerous situations. That consists of the limits of RMS (root mean square) ship accelerations as a function of wave encounter frequencies (ITTC, 1999). Similarly, the importance of considering the acceleration peak values with respect to human health conditions are also illustrated (ISO 2631-26311, 1997). One should note that such situations in vessels can be resulted in temporarily abandoning the assigned takes due to the safety reasons. Undesirable ship motions can be reduced by selecting a better weather profile and proper ship speeds and orientations in unexpected rough weather situations as discussed previously. These dangerous ship navigation situations (i.e. surf-riding, broaching, intact stability, damaged stability, synchronous rolling, parametric rolling, ship operability, and motion sickness) can be denoted by various key performance indicators (KPIs) (Perera et al., 2012d). These KPIs should be organized in a simplified format to improve the information visibility to ship navigators. The KPIs may consist of appropriate and dangerous vessel headings with respect to ship speeds under the respective wave spectra around the vessel. This format can be presented (Perera et al., 2012d) in polar plots, where vessel headings and speeds are represented in polar coordinates. The dangerous regions for ship navigation under the respective heading and speed

4.6.6. Parametric roll Ship navigation in head, following and slightly oblique waves, a half of the ship natural rolling period coincides with the encounter wave period in phase with a large pitch angle, is considered in these situations. Vessels encounter large unstable rolling motions, suddenly with full cycles of pitch/heave for each roll cycle (France et al., 2001) and lose their maneuverability and eventually capsize in such situations. Parametric rolling can increase the ship roll angle from few degrees to over 30° (Levadou and Gaillarde, 2003) in few motion cycles, therefore that is identified as another dangerous situation in ship navigation. Ship parametric rolling occurs under appropriate encounter wave 8



values can be illustrated in appropriate color regions (i.e. red regions) in the same. Additional KPIs with respect to dangerous ship motions and capsizing situations are presented in the recent literature (Kluwe and Krger, 2008). Ship navigators can decide appropriate heading and speed conditions that vessels should follow to reduce rough weather effects by considering such KPIs. Hence, navigator's decision making process is somewhat simplified in such ship navigation situations due to these decision supporting facilities.

mathematical models of vessel hulls. Real-time monitoring data from dynamic loading conditions can also be used to identify other potential dangerous situations in ship navigation such as green water loading, bow slamming, and excessive stresses, shear forces and acceleration conditions (Chen et al., 1998). The critical impact forces on ship hulls under rough weather conditions for various heading and speed conditions can also be observed from the bridge (Adegeest et al., 2009) by the same data.

4.7. Dangerous loading conditions

5. Weather supporting

Ship loading conditions (i.e. weight distribution) are assessed in vessels before leaving the harbors. Those are often calculated by considering loading manuals and stability booklets of vessels. This is an important safety related step that relates to the stability and structural integrity of vessels. In general, ship design loads can be categorized as: still-water, wave-induced, and slamming loads (Kohlmoos et al., 2001). Still water loads consist of the forces due to ship and cargo weights and buoyancy conditions of vessels. Wave induced and slamming loads consist of the forces due to stochastic wave motions (i.e. pressure fields) and sagging conditions of vessels, respectively. At the ship design phase, these loading conditions and respective hull responses under various statistical sea conditions are simulated and the results are verified under model test experiments (Perera et al., 2012b). One should note that the stability of a vessel is also affected by its load distribution. However, load exceedance situations in vessels are also encountered due to human errors in loading calculations (Ioannis and Das, 2006) in some situations. Furthermore, such loading situations can also be challenged by rough ocean conditions in ship navigation situations. Ship responses can also be influenced by nonlinear behavior of the hull, where hull sagging and hogging bending moments may not be equal (Rathje et al., 2003) in some navigation situations. That can generate uneven fatigue conditions in vessels, which can lead to quick hull cracks and structural failures. In model test conditions, longitudinal and transverse load distributions of vessels are calculated and that information is used to estimate bending moments, shear and torsion stresses of hulls (ITTC, 2005c). In loading and unloading situations, actual bending moments, shear and torsion stresses can vary, therefore ship load monitoring mechanisms should be placed to observe these load exceedance situations in vessels. That can reduce the risk of excessive stresses and physical damages to the ship's structures during loading and unloading situations. Cargo load monitoring is currently done (i.e. estimated) by paper based calculations without real-time data. In general, these loading calculations estimate still water bending moments, shear forces, torsion moments and lateral loads that are encountered by ship hulls for the respective angle of heel (DNV, 2011). Furthermore, the parameters of draft, trim, center of gravity, and metacentric height in ships are also incorporated to improve the accuracy of the loading calculations (Rathje et al., 2003). In some situations, paper based loading calculations are replaced by on-board loading computers (Kapsenberg and Thornhill, 2010) but still without real-time monitoring data of actual cargo loads. It is believed that such on-board loading computers should be facilitated with real-time monitoring data of actual cargo loads to improve the calculation accuracy. Hence, that unit (i.e. on-board loading computer) will be one of the most important tools in the bridge, where the most critical ship stability information is held. Real-time cargo load data can be obtained by stress monitoring mechanisms (i.e. several hull mounted strain gauges) as discussed previously. Ship dynamic bending moments, and shear and torsion forces under various navigation situations (i.e. loading and un-loading situations and rough weather conditions) can also be observed under such mechanisms. Real-time monitoring data can also be used to estimate the effects of on the hull ultimate strength and fatigue life by the loading conditions. These calculations are often based on structural

In ideal weather routing situations, vessels should encounter relatively calm weather conditions, where the respective ship performance can be further optimized. Ship navigation situations with following wave, wind, ocean and tidal current conditions can be used to improve vessel speeds. e.g. following winds are used extensively in sail-assisted ship navigation (Ueno et al., 2004) and strong following ocean currents improve ship speeds significantly (Lo et al., 1990; Chang et al., 2013). Furthermore, such weather conditions can be associated with propeller and rudder control systems to lower vessel energy consumption; i.e. vessel rudders can be used to counter the moments due to beam winds during constant heading situations (Journee and Meijers, 1980) and that improves ship speeds and extensively reduces vessel power consumption. Furthermore, offshore operations such as dynamic positioning (DP) can also be benefitted by selecting appropriate ship orientations with respect to actual wave, wind, ocean and tidal current conditions (Fossen and Strand, 2001.) and that can also reduce vessel energy consumption (Perera et al., 2015b). 6. ETD/ETA calculations There are additional measures that can be incorporated into weather routing and safe ship handling approaches to improve navigation conditions and reduce vessel operation costs. Ship navigators use weather forecast to determine the estimated time of departure (ETD) for each voyage, e.g. when to leave the port to avoid potential hazard weather conditions (i.e. freak waves, tropical cyclones and storms). Similar information can also be used to calculate the estimated time of arrival (ETA), where the navigator decides when to reach the port to satisfy voyage objectives. Therefore, both ETD and ETA requirements can be integrated with the respective port schedule to further reduce the ship operation costs. These estimated ETD/ETA and required ship speeds can further be used to estimate the vessel total power requirement that relates to the bunker fuel consumption for the entire voyage. One should note that bunker fuel prices became increasingly volatile and significantly vary among different ports. Hence, that information can be used under ETA/ETD calculations to develop an appropriate fuel purchasing schedule (i.e. ship planning horizon), where the ship operation costs can be further minimized (Brown et al., 1987). Hence, the shipping industry benefits from the estimated ETD/ETA values with respect to weather conditions as discussed above. These ETD/ETA requirements as a part of weather routing can be associated with several route types: shortest path route, least time route, least cost route, best comfort route or any other combination of the same. Similarly, these route types can also be expanded for fleet scheduling and utilization situations in ship navigation. In computer based fleet scheduling (Fagerholt, 2004), the waiting time for vessels in the port can be reduced and that eventually saves both vessel and harbor related operating costs. Furthermore, ship navigation delays with respect to various weather conditions can also be considered and appropriate time adjustments can be introduced in these ETD/ETA calculations. If the ETA/ETD values are estimated accurately, then efficient loading schedules in ports/ container yards can also be arranged for the respective vessels. Furthermore, fleet scheduling and utilization fea9



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Structural Reliability Framework for Floating

tures can also be used to allocate container locations in vessels and facilitate towards better loading and unloading plans (Magirou et al., 1992) for both vessels and ports. That approach can also be expanded to reduce the respective shipping costs further, where the cargo storage can also be optimized. e.g. the cargo allocation for the container storage can be optimized by considering different fright rates under fleet scheduling and utilization (Lacey et al., 2003; Kim and Kim, 1997). As the freight rates and bunker fuel prices can also be fluctuated in different shipping regions, that can also be considered under the same calculations, so called “vessel positioning” problem (Magirou et al., 1992). Furthermore, that can be expanded in other weather related challenges in fleet scheduling and utilization (Fagerholt, 2004). e.g. vessels cannot enter into ports due to draft restrictions under various tidal current conditions. Weather forecast with tidal heights in the port can be incorporated in fleet scheduling & utilization to overcome such situations. That can also eventually improve ship traffic and harbor management conditions. Furthermore, such tools in weather routing and safe ship handling can also benefit to offshore supply and operation vessels and floating offshore platforms that require higher safety margins. The start and end times of offshore operations can be scheduled by using the same tools and safe operational time envelopes can be identified with the required safety and financial constraints. 7. Conclusions Weather routing and safe ship handling are combined by selecting an optimal route with appropriate ship orientations and engine power configurations with vessel design characteristics under forecasted and actual weather conditions (Krata and Szlapczynska, 2012) in this study. Ship speeds can eventually influence by voluntary or involuntary navigation conditions. Voluntary ship speed reductions are used to reduce slamming and extreme ship motions and hull loads. Involuntary ship speed reductions are observed due to added resistance imposed by rough weather conditions (i.e. wind, waves and tide/currents) along vessel routes. Both approaches (i.e. weather routing and safe ship handling) can complement each other in such situations and should be implemented extensively to achieve optimal and safe navigation conditions in shipping. These concepts can be further expended for both vessel and port related optimization approaches in the shipping industry as discussed above. That will be an ultimate navigation tool in future integrated bridge systems and can be used specially in emission control areas to satisfy the respective maritime rules and regulations. Acknowledgment This work is done within the project “HANDLING WAVES: Decision Support System for Ship Operation in Rough Weather”, which has been partially funded by the European Commission, under contract TST5-CT-2006–031489. References Aasen, R., Hays, B., 2010. Method for finding min and max values of error range for calculation of moment of inertia. In: Proceedings of the 69th Annual Conference of Society of Allied Weight Engineers, Virginia, USA, paper No. 3504. ABS, 2004. Guide for the Assessment of Parametric Roll Resonance in the Design of Container Carries. Houston, USA. ABS, 2009. Low Temperature Operations - Guidance for Arctic Shipping. Houston, USA. Adgeest, L.J.M., 2008. Response based weather-routing and operation planning of heavy transport vessels. In: Proceedings of the RINA Conference Marine Heavy Transport & Lift, (London, UK). Adegeest, L.J.M., Hoogerbrugge, B.E., Schiere, M., 2009. Breakwaters on containerships: case study to estimate loads and strength. In: Proceedings of the SNAME 2009, (Rhode island, USA, October). Azaron, A., Kianfar, F., 2003. Dynamic shortest path in stochastic dynamic networks: ship routing problem. Eur. J. Oper. Res. 144, 138–156. Bazari, Z., Longva, T., 2011. Assessment of IMO mandated energy efficiency measures for international shipping. Project final report, Lloyds Register, MEPC 63/INF.2.

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