Derry Port, Co. Londonderry: wind limits for pilotage and crane operations

Derry Port, also known as the Port of Londonderry or Derry Quays, is situated on the River Foyle, approximately 25 km inland from Lough Foyle and the Atlantic Ocean. This location provides a degree of shelter from direct oceanic swells and the full force of westerly Atlantic gales compared to coastal ports. However, the river valley itself can channel winds, and the surrounding topography influences local wind patterns.

The port handles a variety of cargo, including bulk, general cargo, and increasingly, cruise vessels. Operations such as pilotage, berthing, and crane work are sensitive to wind speed and direction. The Wind Agent provides height-matched wind data to assist in operational planning, allowing for comparison against commonly cited working limits.

Wind coming from the north and north-east generally aligns with the river channel, potentially creating less turbulent conditions for vessels. Winds from other directions, particularly those crossing the urban environment or higher ground, may exhibit greater gustiness and shear.

Understanding the current and forecast wind conditions is critical for safe and efficient port operations. The meteogram provides a visual representation of the next five days, showing modelled wind speed, gust speed, and direction at a user-specified height, typically 10 m, 30 m, or 50 m for port activities.

Key elements to observe on the meteogram include:

• Wind Speed and Gust Speed: The solid line indicates mean wind speed, while the shaded area represents gust speeds. The difference between these two can indicate the potential for turbulence.
• Wind Direction: Arrows indicate the meteorological FROM direction. Changes in direction can be as significant as changes in speed, especially for berthing manoeuvres.
• Frontal Passages: Rapid shifts in direction and increases in speed often indicate the passage of weather fronts, which require careful monitoring.

Comparing these forecasts with your operational limits, such as those for crane work or pilotage, allows for proactive decision-making. The Wind Agent's Shear Glass can show the wind at multiple heights concurrently, which is particularly useful for crane operations where boom tip height is a factor.

Wind shear, the change in wind speed or direction with height, is a significant consideration for crane operations. While surface winds may appear moderate, wind speeds can increase substantially at the height of a crane's boom or load. This effect is particularly pronounced in urban environments or near complex terrain.

For crane operators, the commonly cited maximum permissible wind speed for lifting operations typically ranges from 10 m/s (20 kt) to 15 m/s (30 kt) at the boom tip, though specific limits are set by the crane manufacturer and the operator's own risk assessment. Gusts can exert sudden, high loads on the crane structure and the suspended load.

The Shear Glass instrument provides height-matched wind at 10 m, 80 m, 120 m, and 180 m, allowing operators to assess the wind profile through the working height range. A significant difference between the 10 m wind and the wind at higher levels indicates strong shear, requiring increased caution. Night-time often sees increased shear due to atmospheric stability.

Crosswind is a critical factor for vessels navigating the River Foyle and during berthing operations at Derry Port. Strong crosswinds can significantly affect a vessel's ability to maintain its heading and control its speed, increasing the risk of contact with berths or other vessels. Pilotage guidelines and master's standing orders commonly define maximum permissible crosswind speeds for different vessel types and berthing scenarios.

Typical crosswind limits for large vessels during berthing are commonly cited in the range of 20–30 knots (10–15 m/s), though these vary greatly with vessel size, draught, and the specific berth. Winds from the east or west, perpendicular to the river channel, will generate the most significant crosswind component.

The Wind Agent's exceedance fan provides the probability that forecast wind speeds or crosswind components will exceed a user-defined limit at a specific height. This probabilistic information, derived from ensemble models, supports decision-making in marginal conditions, indicating the likelihood of encountering challenging wind conditions.

The prevailing wind direction in the north-west of Ireland is from the south-west, influenced by the passage of Atlantic depressions. However, the specific topography of the Foyle estuary can modify these large-scale patterns at Derry Port.

• Autumn and Winter: These seasons typically bring the strongest winds and most frequent gales, often from the south-west or west. Post-frontal north-westerly winds can also be strong.
• Spring and Summer: Generally lighter wind conditions prevail, though frontal systems can still bring strong winds. Sea breezes may develop on warm, sunny days, typically from the north or north-east, which can be channelled up the Foyle.

The wind rose chart illustrates the historical distribution of wind speed and direction for this location, based on reanalysis data. It provides a baseline for understanding the typical wind environment at Derry Port, allowing operators to compare current forecasts against long-term patterns and identify unusual or challenging wind regimes for the season.

Forecast accuracy is vital for port operations. The Agreement Spine instrument shows the degree of consensus between different weather models and, where available, compares these models against local observations. This comparison helps in assessing the confidence in a given forecast.

• Model Disagreement: When models show significant differences in forecasted wind speed or direction, it indicates higher uncertainty. This is common during complex weather transitions or when local topographical effects are hard to resolve.
• Observation Comparison: Where local Automatic Weather Stations (AWS) or buoys provide real-time data, comparing model forecasts against these observations gives a direct measure of forecast performance. The nearest Met Éireann station at Malin Head (EIMN) or the Met Office station at City of Derry Airport (EGAE) can provide useful regional context, though local conditions at the port may differ.

Discrepancies between modelled and measured data can arise from the spatial resolution of models not fully capturing local effects, or from differences in how wind is measured and reported (e.g., averaging periods, height above ground/sea).

The Wind Agent provides a suite of tools to support operational decisions at Derry Port, by presenting wind data in formats relevant to marine and crane activities:

• Pilotage: Use the meteogram and ensemble plume to assess the likelihood of exceeding crosswind limits during approach and berthing. The Agreement Spine helps gauge forecast confidence.
• Crane Operations: The Shear Glass is crucial for understanding wind at boom tip height. The exceedance fan can quantify the probability of gusts exceeding crane manufacturer limits.
• Ro-Ro and Ferry Berthing: These vessels are particularly susceptible to crosswind. The fan instrument can help assess the risk of exceeding berthing limits for specific vessel types.
• Load Planning: For cargo operations, understanding gust potential and shear is essential for safe lifting and securing of loads. The gust factor chart can provide insight into expected gustiness.

All decisions remain with the operator, informed by their own risk assessments, vessel characteristics, and port-specific procedures. The Wind Agent acts as a precise instrument to provide the wind evidence required for these decisions.