The nationwide demand for energy is fueling development of sustainable offshore wind resources. To reach the strong and steady offshore wind resources, the Bureau of Ocean Energy Management (BOEM) will lease the seabed on the outer continental shelf for offshore wind farms. But the prospect of offshore wind turbines anchored to the seafloor in the Atlantic Ocean has raised questions about potential risks to commercial shipping traffic as vessels maneuver around the installations. Sponsored by BOEM, and in close coordination with BOEM and the U.S. Coast Guard, the Pacific Northwest National Laboratory (PNNL) has developed an assessment of navigation safety risks, by:

• Processing and filtering transponder data (Automated Identification System [AIS] data) from all commercial shipping on the Atlantic
• Geospatially analyzing the AIS data to determine historical shipping routes
• Developing a data-driven numerical model to predict vessel movements in the presence of offshore wind farms
• Enlisting maritime expertise from an experts’ panel of pilots, ship captains, industry experts, and federal agencies
• Assessing the marginal increased navigation risk to ships from the presence of offshore wind farms.

The AIS dataset for shipping in the United States is very large (several billion points) and represents a significant challenge to handle and analyze. PNNL researchers extracted information for each of the 20,000+ vessels, including the tonnage, dimensions, horsepower, displacement, and routes travelled by the ship over a 3-year period. Beginning with methodologies developed for wind farms and shipping in the United Kingdom, PNNL developed new geospatial analytical tools to determine the commonly traveled routes among the 28 major ports on the Atlantic, displaying them as GIS layers. Using the AIS data and geospatial routing, a numerical model was developed that moves ships in a realistic manner for the base case (present conditions with no wind farms) and the future case (with planned wind farms). Each case was also run as scenarios with confounding conditions, such as hurricanes or Nor ‘Easters, with loss of propulsion of one or more ships. For the base case, the model maneuvers ships around other vessel traffic, existing hazards, and moves them in and out of ports. The future case with wind farms adds maneuvering of ships around the wind farms, as well as avoiding other ships funneled into the same waters. The rules of road, as practiced by mariners, are incorporated into the model to enable the ships to behave as they would in the real world.

The Atlantic fleet of commercial vessels was parsed into three major categories: cargo, tankers, and tug/towing. Each vessel type has individual characteristics for routing in and out of ports and individual challenges when maneuvering around wind farms. Cargo and tanker vessels cannot change course or slow rapidly, and they need deep draughts for entering harbors. Tugs and towing vessels come in many different configurations that include large articulated tugs, strings of several barges towed by catenary wire by one tug, and “wing and ground” configurations of tugs pushing perpendicular to barges. The model generally sends tug and towing vessels inshore to avoid wind farms, while cargo and tanker vessels go further out to sea. 

PNNL researchers are continuing to refine the model, improving the realism of ship routing and encounters. The preliminary study results indicate that the presence of wind farms on the Atlantic coast could increase the risk of vessels coming within one half mile of one another (an “encounter”) by approximately 12% and groundings caused by avoidance of wind farms could increase by less than 1%. It is likely that the increased risk of encounters between ships will drop as further refinements are added to the model, including improved route planning, as would be expected by large shipping companies, and more detailed bathymetry of the coastal areas. These improvements will raise confidence in the predictive capability of the model and allow it to act as a better tool for evaluating the safety of wind farm installations.

The results of the navigation risk project will be presented in the poster session at the American Wind Energy Association’s Offshore WINDPOWER 2014 Conference & Exhibition in October in Atlantic City.