Offshore survey vessels (geophysical, metocean, wind farm development): the wind call, at your height

As a Party Chief or Marine Coordinator, you make daily decisions to plan survey lines and manage standby periods. These calls are based on predicted wind conditions. A critical part of your role is to ensure survey operations proceed efficiently, making the most of favourable weather windows.

These daily decisions directly impact project timelines and budgets. Incorrectly calling a weather window can lead to vessel downtime, delaying the survey campaign. Conversely, deploying towed gear in unsuitable conditions carries operational risks.

Your decisions are guided by your vessel master's input and client specifications, which often include limits for wind speed. The Wind Agent focuses on wind at your working height, providing detailed odds to support your planning.

While the exact cost of a wrong call is not quantified here, it commonly includes day rates for vessels on standby and the potential for damage or operational delays. The goal is to minimise these costs by making informed, timely decisions about when to proceed or hold.

Your work requires precise knowledge of wind conditions at your operational height. The Wind Agent provides wind forecasts at 10, 80, 120, and 180 metres, interpolated to your specific working height. For offshore survey work, this is typically set at 10 metres, as specified in your instrument's preset.

Understanding the difference between mean wind speed and gusts is vital. Gusts are short, sharp increases in wind speed that can significantly impact operations, even if the mean wind speed is within limits. The instrument shows both the mean wind speed and gust speeds side-by-side for each forecast hour.

Your operational limit for wind speed, often expressed in knots, is set by your vessel master and client specifications. This limit is a key input for the instrument, allowing it to compute the odds of exceeding that threshold. It is always your own document that governs the specific limits you operate under.

When you set your working height at 10 metres, the instrument shows the wind conditions relevant to your immediate operational environment. This helps you assess the suitability of conditions for deploying equipment or running survey lines.

The instrument computes the probability, or odds, that wind speeds will be above your set limit for each hour. This is derived from an ensemble of weather models. If 20 out of 100 model runs predict wind above your limit, the odds are 20 per cent. This is the fraction of ensemble members that exceed your threshold, not a calibrated certainty.

Where weather models agree, the Agreement Spine will show a tight cluster of predictions. Where they do not, the spine will spread, indicating higher uncertainty. This spread is distinct from the odds, which are about your specific limit. A high percentage of ensemble members above your limit suggests a higher risk for your operation.

For example, if the odds of exceeding your limit are 20 per cent, you might proceed with caution, knowing there is a relatively low risk. If the odds are 50 per cent, you would likely reconsider or delay, as there is an equal chance of conditions being unsuitable. At 80 per cent, you would almost certainly hold, as the risk of exceeding your limit is very high.

These percentages provide a framework for assessing risk in your daily planning. The decision to proceed or stand by is always yours, based on your experience, your vessel's capabilities, and the specific requirements of your survey. The instrument provides the objective data to inform that decision.

This is an example of how you might use the instrument in your daily planning:

• 06:00: You log in and check the 16-day ensemble odds. The forecast for tomorrow morning shows a 20 per cent chance of wind speeds exceeding your 20-knot limit at 10 metres. The Agreement Spine shows good model consensus for the next 48 hours.
• 07:00: You review the Morning Brief (Pro plan feature), which confirms the low odds for tomorrow. You decide to plan for an early start to survey line deployment, aiming to complete the work before any potential increase in wind later in the day.
• 12:00: A quick check shows the odds have not changed significantly for tomorrow. You brief the vessel master, confirming the plan to deploy towed gear in the morning.
• 18:00: You check the forecast again before the end of the day. The odds for tomorrow morning remain at 20 per cent. You confirm the operational plan for the following day, confident in the window for deploying equipment.
• 22:00: Before turning in, a final check confirms the forecast. You are prepared for the next day's operations, having used the instrument to inform your decision-making throughout the day.

Your operational limits for wind speed are not set by the instrument; they come directly from your own operational documents, such as your vessel's operating procedures or client specifications. These documents define the maximum acceptable wind speeds for specific survey tasks, particularly when deploying sensitive towed gear.

When you first use the instrument, you will input your specific wind speed limit. This value, for example, 20 knots, is then used by the instrument to calculate the P(above your limit) odds for each hour. The instrument is preset to a working height of 10 metres, reflecting the typical height relevant for offshore survey operations.

It is important to remember that the instrument does not make the decision for you. It provides data based on the limit you provide. You, as the competent person on site, use this information in conjunction with all other relevant factors to make the final call.

Regularly reviewing and updating your limit within the instrument ensures that the odds displayed are always relevant to your current operational requirements. This direct link between your documented limits and the instrument's calculations provides a practical tool for risk assessment.

For offshore survey operations, maintaining a detailed record of weather conditions and operational decisions is important. The instrument provides a dated record page that logs what was forecast, what was observed, the wind limit you used, and the call you made (to proceed or stand by).

This record serves as an objective account of the weather conditions that influenced your daily decisions. In an industry where weather downtime can be a significant cost, having a clear, auditable record can support claims or discussions regarding weather-related delays.

Clients or project managers often request such records to understand the rationale behind operational choices, particularly when unexpected delays occur. Your ability to demonstrate that decisions were made based on the best available meteorological data adds to your professional standing.

The record page helps you review past forecasts against actual observed conditions, allowing you to refine your understanding of local weather patterns and model performance. This continuous learning contributes to more informed decision-making in future campaigns.

Ireland's offshore environment, particularly with its Atlantic exposure, presents unique challenges for survey operations. The storm season, generally from October to March, brings higher probabilities of strong winds, often limiting survey windows. The primary survey season typically runs from April to September, when conditions are generally more favourable.

However, even during the summer months, rapidly changing weather systems are common. Accurate wind forecasting is therefore crucial for planning survey lines and managing standby periods efficiently, whether you are working on sites off the east coast or in the Celtic Sea.

Met Éireann, as the national forecaster, provides general meteorological guidance, but your work requires site-specific wind data at your operational height. The instrument provides this detailed, height-interpolated wind information, allowing you to assess local conditions more precisely.

Understanding the seasonal variations and the potential for sudden weather shifts is key to successful offshore survey campaigns in Irish waters. The instrument assists in navigating these conditions by providing forward-looking wind odds, helping you to identify and utilise suitable weather windows for your critical work.