Sophistication of weather routing grows
Weather routing typically relies on only one weather forecast source, says Dr Henry Chen, Chief Naval Architect at Jeppesen Marine. In the US, surface pressure, wind and sea state forecasts are available as free downloads over the internet from NOAA. While the quality of such forecasts may be good enough for weather routing, their level of detail is not sufficient for ship motion response prediction and voyage optimisation. This is particularly true in predicting the sea and swells generated by tropical cyclones since meteorologists often issue vastly different forecasts from the model predictions.
“National centres such as NCEP/NOAA, US Navy, UKMET, JMA and ECMWF are routinely producing long-range wind and wave forecasts 15 days ahead and beyond. However, the accuracy of each model varies due to model resolutions, how the physics is implemented, and many other factors. The centres tend to calibrate their models to perform better when storms threaten their own countries, but pay less attention to mid-ocean storms passing shipping lanes,” says Dr Chen.
None of the models can consistently produce accurate forecasts for tropical cyclones due to their complex physics and rapid development. Human forecasters are employed during the hurricane seasons to issue track and intensity forecasts based on consensus of model outputs as well as past experience. Accuracy starts to deteriorate after 3-5 days, leading to even larger uncertainties between 5-7 days.
“Currently, the best approach to ocean weather forecasts is to adopt a ‘man-machine’ mix in which experienced forecasters quality-control the sea surface pressure forecasts, including the wind fields derived from the track and intensity forecasts from various forecast centres,” says Dr Chen.
This means the best of each national centre’s forecast are taken and uncertainties can be quantifies. At each grid point in every forecast horizon extending to beyond 15 days, the values for mean and standard deviation can be used to judge the accuracy levels of the forecast. “This type of consensus knowledge will provide greater insight in selecting the optimum route, taking into account the risk of heavy weather damage as well as predicted fuel consumption for virtual arrival due to forecast uncertainties.”
Jeppesen’s voyage optimisation technology therefore provides more accurate wind and wave forecasts and takes into account sea surface currents since they can also significantly impact ship speed and fuel consumption. High-resolution global circulation models enhanced by satellite measurements can now produce accurate daily depictions of major currents and eddies. Jeppesen technology is also able to determine ship design criteria such as speed, sea margin, maximum ship motions, and bending moment by repeatedly simulating voyages using historic wind and wave hindcast databases.
Oceanographic company Tidetech has started providing tidal streams, ocean currents, sea surface temperatures, wave data and meteorological forecasts for commercial shipping. Much of the information is not obtainable anywhere else, says Tidetech managing director Penny Haire. “Route and speed optimisation using tide and current data go beyond weather routing in that it results in additional bunkerage savings and efficiencies that are unrelated to weather.
“A key point of difference is oceanographic data can be applied to deep ocean and coastal routing, as well as restricted navigation channels, whereas weather routing is a deep ocean, or Pilot-to-Pilot, service.” Tidetech claims that very little capital investment is required to integrate the data into existing systems.
In a trial with a major cruise line earlier in 2012, bunker savings of one to four per cent were shown on routes using the Gulf Stream currents between Florida and Mexico. Further analysis has revealed that applying speed optimisation can create significant single-trip savings when optimising vessel speed through restricted navigation channels such as the English Channel and the Malacca Straits. Tidetech is currently running ship efficiency trials aboard a cruise ship in Asia and on container vessels worldwide. Results are expected in early 2013.
Applied Weather Technology (AWT) recently launched a new web page that provides sea ice concentration information that is updated daily. AWT monitors The National Ice Center and The National Center for Environmental Predictions Marine Modelling and Analysis Branch in order to provide the most accurate information possible. The data is remotely sensed sea ice concentrations enhanced by analysts to incorporate all additional available ice data. It is based on a 5 minute latitude/longitude grid which equates to about one nautical mile in the polar region. While the images shown on the website give an overall perspective, the data is also available to clients in much higher detail and can be sent to ships via email or included on their charts if AWT weather routing services are engaged for the voyage.
