Chapter Twenty Two CHAPTER TWENTY TWO Weather Routeing INTRODUCTION The technique of weather routeing is that of using all available meteorological and oceanographic information to enable a vessel to make the safest quickest and most economical passage Climatological weather routeing implies taking advantage of favourable permanent and seasonal wind systems, (e.g., trade winds and monsoons or prominent ocean current5) and this has been practised by ship masters for hundreds of years The shortest route is not necessarily the quickest The modern form of weather routeing means taking advantage of the information derived by meteorologists from actual and forecast synoptic weather maps in order to avoid the worst of the weather in the mobile weather systems of the temperate zones It seems not inappropriate, therefore, to refer to it as "synoptic 'weather routeing” This modern technique primarily involves trying to keep the ship clear of the areas of highest sea and swell waves, which are the main cause of speed reduction and of risk of damage to the ship and her cargo A rudimentary form of this technique can be practised by a shipmaster himself nowadays by interpretation of the facsimile weather maps broadcast by radio from meteorological services These maps portray actual and forecast wind force, and wave heights along his route Alternatively the master can arrange to be given regular routeing advice by radio in certain oceans, by specialised meteorologists ashore, on a prepayment basis CLIMATOLOGICAL WEATHER ROUTEING The Indian Ocean because of the reversal of direction and differing characteristics of the NE and SW Monsoon winds with their resulting surface currents has always been a fruitful area for climatological weather routeing First practised by the Arab dhows, then by sailing ships of western nations and then by power-driven ships, it is still used there fairly regularly today Other practical examples include the exploitation of the north-going Gulf Stream and south-going inshore current, respectively, off the United States east coast and of the route via the Azores for low-powered westbound Atlantic shipping Valuable advice about climatological routeing is given in the Admiralty publication Ocean Passages for the World The International Loadline Zone Charts illustrate a compulsory form of climatological routeing in that they 205 Chapter Twenty Two restrict the draught of ships in certain ocean areas during very unfavourable seasonal weather SYNOPTIC WEATHER ROUTEING Formerly information to enable mariners to plot their own synoptic charts was transmitted by radio in the form of a numerical analysis However skilled were those plotting this took a disproportionate amount of time on hoard The result was also based on reports which would have been made several hours beforehand This has been revolutionised by the access to facsimile weather maps which are now broadcast by radio by numerous national meteorological services These can be received onboard by relatively inexpensive equipment and provide immediate up to date situations In addition it is possible for satellite transmissions to be received directly (see Chapter 19)." The master of a ship equipped to receive the facsimile maps has at his disposal, at 12-hourly intervals maps prepared by experts showing actual and forecast wind direction and force with fronts, isobars and, in the North Atlantic and Pacific, wave heights Armed with these maps plus the written weather bulletins received by radio he is better able than ever before to take evasive action He is further helped in this by the relatively high speed of his modern ship WEATHER ROUTEING ADVICE FROM METEOROLOGISTS ASHORE Synoptic weather routeing from the shore implies that, at the request of a shipowner a meteorological service or commercial meteorologists advise the master of a ship on sailing as to the best initial route to take on the basis of the meteorological situation They correct this advice if and when necessary as the voyage progresses This technique was initiated in the USA and since 1954 the US Navy have regularly routed their military sea transport ships while US commercial meteorologists have provided a similar service to any merchant ships that pay for it In 1960 a weather routeing organisation was started by the Netherlands authorities and in 1968 by the British Meteorological Office These services have now expanded to comprise not only METROUTE, the International Ship Routeing Unit but also a Sea-ice report service and a Marine Advisory and Consultancy Service There are also private commercial operations offering similar services The high degree of success attained by modern weather routeing from the shore has been made possible mainly by: (a)The network of observations from merchant ships in the North Atlantic and North Pacific (especially the Atlantic) (b) The availability of the high speed electronic computer to the meteorologist This makes possible the rapid evaluation of present and future 206 Chapter Twenty Two wind speed and wave contours thus enabling him to look further ahead than ever before (c) The high percentage of merchant ships with speeds in excess of 15 knots Relatively fast ship speed facilitates bold deviations on passage when necessary to avoid high wave areas (d) The availability of information regarding wave heights obtainable from satellite transmissions It is reasonable to suppose that a professional forecaster armed with so many facilities should be able to get more consistently good results than the shipmaster can on ills own The master of a fast ship in the North Atlantic cannot always spend time on weather maps and it may well pay him to restrict his own routeing to occasions when shore facilities are not available All authorities which provide weather routeing advice from the shore use broadly similar methods The service provided needs to be tailor-made for the ship concerned The first essential step is to prepare curves for each ship or class of ship that is to be routed, showing how much her speed is reduced in waves of various heights at the light and loaded draft Specimen curves are shown at Figure 22.1 Such curves can be quite approximate and may if not otherwise available be constructed from data in the ship’s log book In the case of a new ship, if curves were not prepared in the experimental tank those from a similar class of ship might be used as a temporary measure When a ship is being routed the meteorologist studies her performance curves against the background of the forecast wind and waves along the ship's intended route from a study of charts prepared with the aid of the electronic computer He then prepares an initial "least time track" for as far ahead as he feels able to forecast, this may be anything between 24 and 72 hours depending upon the complexity of the synoptic situation An example of a “least time track" is at Figure 22.2 showing some 48-hour least time track curves (plotted for 12 hour intervals) from Belle Isle towards Bishops Rock In this case the advised track is the great circle because it cuts that part of the curve which is nearest to the destination Obviously the most adverse conditions are to the northeastward This track may be modified in the light of other aspects such as surface currents, ice or estimated synoptic development during a further 24 or 48 hour period The master of the ship will be advised as to the recommended initial least time track before sailing This recommended route may be amended as and when necessary on the basis of further "least time tracks" prepared at 12 hourly intervals as the voyage progresses It is essential that every ship that is weather-routed sends a weather message every six hours throughout the 207 Chapter Twenty Two passage so that the routeing authority can follow her progress An important feature of any such service is that the weather routeing team includes professional seamen as advisors to the meteorologists The procedure used by the British Meteorological Office is as follows The meteorologists work in conjunction with master mariners with command experience One of their jobs is to maintain personal liaison with the master of each routed ship and to get details of the ship and her performance This implies obtaining or else personally constructing from available data, her speed, wave height curves, fuel consumption and probable draughts, also liability to carry deck cargo and any special wishes of owners and master They the navigational work connected with the routeing, calculate distances on alternative routes and the likely effects of adverse and favourable currents, keep up to date with ice conditions and ensure that routeing signals to the ship are unambiguous Before the ship sails from a home port they give the master the initial advice by phone and this is followed up by a confirmatory radio message Communications play an important part in weather routeing and these are kept as brief and infrequent as possible so as to reduce cost For example the initial signal to a ship sailing from Liverpool to New York might read '"Advise via FASTNET thence thumb to 20oW thence circle Nantucket" At the end of the voyage the master is sent a track-chart showing the actual route and the winds experienced, also the winds that would have been experienced if the conventional route had been followed (See Figure 22.3.) Experience has shown that despite adding as much as 300 miles to a 3000 mile passage both time and fuel can be saved Just as importantly, there can be a considerable reduction in risk of damage to both ship and cargo METROUTE, the routeing advice service of the UK Met Office will provide a detailed price guide on request The service is extremely comprehensive; routeing advice is available ranging from relatively short European area voyages to all oceans of the world 208 Chapter Twenty Two QUESTION S What are the general principles involved in climatological weather routeing? Give examples Describe the modern methods of weather routeing and the information and facilities normally available to the shipmaster to enable him to practise his own routeing Discuss the general organisation and practical procedure used by the British Meteorological Office when routeing a ship on a N Atlantic crossing What are the proven advantages of this system on average? 209 Chapter Twenty Two 210