19 CHAPTER 2 Appraisal 2.2.1.5 Speed and Endurance The overall speed required to achieve the ETA can now be calculated. Consider whether any of the following will affect the calculated overall speed: ?Speed constraints –economical speed and maximum speed –environmental conditions –limits and restrictions –machinery limitations and defects ?endurance constraints –bunker capacity –fuel economy –minimum reserve of fuel –bunker availability –stability/loadline considerations –stores and spare parts –provisions and fresh water –manning considerations. To conduct the majority of a passage at an economical speed, it may be necessary to proceed for a short period at a higher speed. If using ECDIS, the ETA to the final waypoint will update as the voyage progresses, enabling the speed to be adjusted accordingly. Alternatively, the formula shown in Figure 16 can be used to calculate the time necessary to proceed at higher speed to reduce to an economical speed for the remainder of the passage. t = Where: t = time required to proceed at higher speed D = distance (nm) from start of passage to point of arrival T = time (hours) from start of passage to required ETA at point of arrival O = higher speed (kts) to be used H = economical speed (kts) For example: The navigator is planning a passage for a ship with an economical speed of 10 kts and a maximum speed of 16 kts. There are 42 hours to complete the passage of 500 nm between departure and arrival points. The average speed required overall is therefore: 500 nm/42 hrs = 11.9 kts. Therefore, the length of time to proceed at a higher speed (16 kts) in order to reduce to the economical speed (10 kts) for the latter part of the passage is: t = = = = 13.33 or 13 hrs 20 mins Speed Time Distance travelled 16 kts 13 hrs 20 mins 213.33 nm 10 kts 28 hrs 40 mins 286.67 nm Total: 42 hrs 500 nm The navigator should then compare the fuel consumption figures to see whether initially increasing the speed to complete the majority of the passage at an economical speed will achieve an overall saving in fuel compared to proceeding at 11.9 kts for the entire passage. Figure 16: Calculation to determine the time remaining at a higher speed, prior to reducing to a lower speed for the latter part of a voyage, while maintaining the required ETA. If by this stage the voyage criteria are assessed to be unachievable, the Master should be advised at the earliest opportunity. Passage Planning Guidelines 20 2.2.2 Preliminary Research – Weather and Environment The weather, and any other environmental factors likely to affect the passage, should now be considered. It will be necessary to gather climatological, meteorological and oceanographic data to estimate the weather most statistically likely for the passage. Publications such as ‘Routeing Charts’ and ‘Sailing Directions’, published by competent authorities, should be consulted for this purpose. If planning is taking place immediately prior to commencing a passage, an up-to-date weather forecast should be obtained. The following factors should be considered: ?Historic weather statistics (see Figure 17) –mean pressure –mean temperature –precipitation –visibility and probability of fog –wind strength (see Figures 18, 19 and 20) –hurricane, cyclone or typhoon seasons (see Figure 21) –wave height and direction (see Figure 22) ?load line limits –depicted on ‘Routeing Charts’ for the major oceans, by month Figure 17: Historical climate information for Milford Haven. (UKHO, NP37 – ‘Admiralty Sailing Directions, West Coasts of England and Wales’?) (Courtesy of UKHO) 21 CHAPTER 2 Appraisal Figures 18, 19 and 20: Wind direction, frequency of gales and swell distribution for the west coast of the UK in May. (UKHO, NP37 – ‘Admiralty Sailing Directions, West Coasts of England and Wales’?) (Courtesy of UKHO) Figure 21: Historical information relating to tropical storm frequency. (UKHO, NP136 – ‘Ocean Passages for the World’?) (Courtesy of UKHO) Passage Planning Guidelines 2223 CHAPTER 2 Appraisal Figure 22: Percentage frequency of wave heights for July. (UKHO, NP136 – ‘Ocean Passages for the World’?) (Courtesy of UKHO) Passage Planning Guidelines 24 ‘Routeing Charts’ provide information additional to that given in ‘Ocean Passages for the World’ and ‘Sailing Directions’ (see Figures 24 to 27). Figure 24: North Atlantic Routeing Chart for July. (UKHO, Chart 5124(7)) (Courtesy of UKHO) Figure 25: North Atlantic Routeing Chart for July. (UKHO, Chart 5124(7)) (Courtesy of UKHO) Figure 26: North Atlantic Routeing Chart for July showing tropical storm tracks and percentage frequency of winds greater than Force 7. (UKHO, Chart 5124(7)) (Courtesy of UKHO) Figure 27: North Atlantic Routeing Chart for July showing percentage frequency of fog. (UKHO, Chart 5124(7)) (Courtesy of UKHO) ?likely statistical environmental conditions –ice limits –ocean currents –tidal streams for coastal passages (see Figure 23). Figure 23: Predicted direction and rates of tidal stream shown in tidal stream atlas. (UKHO, NP256 – ‘Tidal Stream Atlas, Irish and Bristol Channel’ ) (Courtesy of UKHO) 25 CHAPTER 2 Appraisal ‘Ocean Passages for the World’ (OPTW/NP136) In 2018, the UKHO released a significant update to ‘Ocean Passages for the World’ (OPTW). The 2018 edition of NP136, Volume 1 (Atlantic Ocean) and Volume 2 (Indian and Pacific Oceans), was based on empirical research and depicts the results of a one-year sample of global (satellite and terrestrial) AIS data for worldwide bulk carrier, passenger ship, container ship and cargo ships’ actual AIS tracks. The book removes any distinction between high-powered and low-powered ships, makes waypoints available in a format useful to ECDIS users and overlays ocean currents onto the route diagrams for the first time. Admiralty OPTW (NP136, Vol 1/2) contains ‘overview’ information at the beginning of each geographical volume, which provides information on how to use each guide during the passage planning process. This overview section also provides information about each geographic area, regarding: ?Natural conditions ?climate ?winds, seasonality, TRS, depressions ?weather, waves and swell ?currents ?ice ?coral ?magnetic anomalies. The overview section provides a broad description of global maritime weather patterns and other considerations relevant to ships crossing the ocean covered by that volume. The diagrams are similar to those found in ‘Sailing Directions’, but for ocean areas. The subsequent sections of OPTW are organised by ocean region and detail the most frequently used routes between the most frequently used ports, identified by AIS analysis. Each section shows the routes in both a map/graphic diagram format and a tabular format. Each waypoint is named and the start and end of each route typically coincides with coastal routes detailed in ‘Sailing Directions’. Each geographic section has a diagram at the start of the chapter showing each of the most frequently used ports, with the routes connecting them listed by name. The beginning of the section also lists cautionary notes particular to the region, naming hazards, currents and natural conditions that may be encountered there. The routes given may be either ‘port to port’ or ‘connector’ routes. Connector routes span multiple sea areas. Routes may be Rhumb Line (RL), Great Circle (GC) or Composite GC and the distance of the route is listed. Figure 28: NP136, Vol 1, pg 43 – Screenshot from Admiralty Gateway eNP version, North Atlantic Connector Routes, UKHO 2018. Passage Planning Guidelines 26 Figure 29: NP136, Vol 1, pg 44 – Screenshot from Admiralty Gateway eNP version, Corresponding waypoints, UKHO 2018. The Ocean Connector Routes: ?Take account of the start or end of ocean TSSs ?do not account for coastal or inshore TSSs (port approaches) ?do not account for Load Line Zones ?do not account for hazards that may be shown on better scaled charts/ENCs ?make no distinction between high-powered/low-powered ships ?are described as ‘Port to Port’ or ‘Port Connector’ routes ?can be used in either direction. The Ocean Connector Waypoints: ?Are all named ?are given a unique ID number ?are given to degrees and minutes accuracy (DD° MM’). The routes are shown graphically on map diagrams at an overview scale and the routes are overlaid on arrows depicting the magnitude and direction of the surface currents known to affect shipping. The currents shown are for the month of January and are intended to be used as a general guide only. Navigators using these waypoints, routes and current diagrams should use them as an initial approximation for a route, before doing further detailed planning using a more accurate current and tidal stream prediction. Admiralty ‘Routeing Charts’ give more detailed predictions of the likely currents for each month, season and ocean region. 27 CHAPTER 2 Appraisal Figure 30: NP136, Vol 1, pg 108 – Screenshot from Admiralty Gateway eNP version, Port to Port Routes, UKHO 2018. The table of ports in each section includes the ‘UN Code for Trade and Transport Locations’ (LOCODE) and ‘UN Country Code’ (CCODE) for each named port, to avoid misidentification between ports with the same name. Geographic Positions (GPs) are given for each waypoint in the format of DD° MM’ and need to be adapted more precisely when plotting courses to steer on detailed charts/ENCs. Figure 31: NP136, Vol 1, pg 109 – Screenshot from Admiralty Gateway eNP version, Corresponding Port Waypoints and Port Codes, UKHO 2018. Passage Planning Guidelines 28 In addition to the use of printed publications for assessment of weather and environmental information, some ECDIS can integrate with weather routeing services. Where this capability exists, it may be necessary to construct a route in ECDIS, although an approximate route is all that is required at this stage. Figures 32 and 33: Some ECDIS passage planning software facilitates the simulation of likely weather conditions, allowing optimal routes that avoid certain weather patterns to be identified. (Courtesy of Transas) 29 CHAPTER 2 Appraisal It is also possible to use ECDIS to display chart products that can help ascertain the existence or extent of ice. This is particularly important when planning to use a GC route at high latitudes or when planning to travel through or near areas that are prone to ice formation (see Figures 34 and 35). Figure 34: An example of an ice chart overlay. (Courtesy of Transas) Figure 35: A satellite image that can be used to show ice formation relative to land mass. (Courtesy of Transas) Passage Planning Guidelines 30 2.2.3 Preliminary Research – Passage Planning Guides These Guides, produced by Witherbys, are updated on a two-year cycle to incorporate the latest guidance and practical advice for ships transiting the following regions: Straits of Malacca and Singapore (SOMS)Great Barrier Reef and Torres Strait (GBRTS) English Channel, Dover Strait and Southern North Sea Figure 36: Witherbys regional Passage Planning Guides. The Guides bring together all the regional information required in the appraisal and planning stages and have been carefully compiled with the assistance of navigating officers, ship Masters, deep sea pilots, marine advisors, navigation superintendents and other appropriate organisations that have an interest in the respective regions. Figure 37: Extract from the English Channel, Dover Strait and Southern North Sea Passage Planning Guide. The Guides include full-colour pull-out chartlets that accompany detailed passage information for each leg of the voyage, ensuring that they provide ongoing support and guidance during the complete voyage through the area. Figure 38: Extract from the Straits of Malacca and Singapore (SOMS) Passage Planning Guide.