Structural icing is largely defined by sea and air temperature and wind speed. Read more…

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Each time of year brings it’s own weather dangers and winter is no exception. As the temperatures cool down, ships in the northern hemisphere are increasingly at risk for structural icing. In this month’s article Mike O’Brien, AWT’s Senior Operations Manager, describes the danger of structural icing and explains what factors AWT uses to predict when structural icing will develop. The structural icing forecast is one of the several features available through AWT’s BVS software. As always, we welcome your feedback. Skip Vaccarello Structural Icing Mike O’Brien, AWT’s Senior Operations Manager The approach of winter in the northern hemisphere brings a variety of weather challenges to shipping. Mid latitude systems become more intense with increasingly heavy seas along with colder sea and air temperatures. The phenomenon we are concentrating on here, structural icing, is largely defined by the sea temperature, the air temperature and the wind speed. Structural icing is most common in the northern hemisphere shipping lanes during the months of January, February and early March over the NW Atlantic and the Gulf of St. Lawrence, the Baltic Sea, the Bering Sea and along the Kuril Islands of the western Pacific. What is structural icing and what is the danger? Structural icing occurs when water spray, blown by the wind, freezes to the deck, deck equipment and superstructure of the vessel. The accumulation of ice on deck poses an immediate, obvious risk to the crew operating on deck. A more ominous risk, however, exists when icing continues to build on the deck resulting in a change in the stability and/or trim of the vessel due to the weight of the ice. If a vessel continues to experience the building weight of the ice on the forward portion of the vessel, she could quickly become trimmed down by the head or become “top heavy’. Once these changes to the vessel stability take place there is an increased risk for catastrophic vessel motions, especially if the sea conditions are rough. How do we forecast where structural icing will develop? Forecasting when there will be a risk for structural icing requires the input of predicted conditions for the air temperature, the sea temperature and the wind speed. Once these values are determined, the risk for structural icing can then be evaluated. With colder air temperatures, colder sea temperatures and heavier winds, the risk for structural icing will increase. At a minimum, there generally needs to be air temperatures below zero degrees centigrade, sea temperatures below five degrees and winds above 18kts before there is any significant risk for structural icing. Structural icing rates are defined as:       None       Light = less than 20.32 mm per 3 hours       Moderate = less than 60.96 mm per 3 hours       Heavy = greater than 60.96 mm per 3 hours In addition to these environmental factors that make structural icing possible, another key ingredient is the heading of the vessel, in relation to the wind. Given environmental conditions that are favorable for moderate structural icing, a vessel heading into the wind will accumulate ice more readily than a vessel with the wind on the stern. The breaking waves on the bow create more spray, freezing on the vessel deck and superstructure. BVS Displays the Risk for Structural Icing AWT’s BVS 6 software contains a variety of tools to aid in voyage planning while at the same time providing a wide range of forecast information. It contains a structural icing forecast which is available to the Master by selecting the appropriate icon in the easy-to-use BVS graphical display. The Master can quickly see if there will be a risk for light, moderate or heavy structural icing along the vessel track. The system uses a graduated color coding on the display map to clearly indicate where the risk for these conditions will exist. AWT strives to continuously improve our systems and the addition of the structural icing feature in BVS 6 is an example of our commitment to vessel safety.

BonVoyage System Marine voyage optimization system provides 24/7 on-board weather… more > BonVoyage System & Ship Routing Combination of BonVoyage System & AWT’s ship routing services… more > GlobalView Fleet Management Quickly monitor your fleet & ensure they are operating efficiently & safely… more > Ship Routing – Earliest Arrival Our weather routing experts recommend the optimum route analyzing… more > Ship Routing – Fuel Optimization Improve schedule integrity & minimize fleet’s fuel consumption… more > Tracking/Global AIS/Polling Tracking & automated satellite position polling service locates vessels… more > Offshore Support Pre-departure route planning & forecasting en-route… more > Arbitration Support & Forensic Studies Prepared reports for use in arbitration & legal venues… more > AWT is the leading provider of fleet optimization services, ship routing services and BVS onboard voyage management software to ship owners, operators and charterers seeking the safest and most efficient routes for their fleets. AWT is staffed by world-renown experts in ship routing, meteorology, IT, maritime science and former mariners who are focused solely on the maritime industry. Using the most sophisticated technology, AWT routes more ships per month than any other company. Its superior customer service and integrity have made AWT the most trusted fleet optimization provider in the maritime industry. Founded in 1996, AWT is headquartered in Sunnyvale, California with worldwide offices located in the UK, Hong Kong, Shanghai, Korea, Japan, Singapore, Germany, New York, and New Jersey. More information is available at www.awtworldwide.com or by calling +1.408.731.8600.

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