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Understanding weather downtime in your outputs

What is Weather Downtime?

Weather downtime represents the percentage of time that your logistics operations (vessels and equipment) cannot perform their tasks due to unsuitable weather conditions. This is one of the most critical factors in wind energy projects, as weather significantly impacts construction and maintenance schedules.

How We Track Weather Downtime

During your simulation, our system continuously monitors each logistics unit (vessel, helicopter, etc.) and tracks:

  1. Active Time - The total hours when the logistics unit is available to work based on your availability settings
  2. Time Waiting for Weather - The hours when the unit cannot operate because weather conditions exceed your defined limits

The weather downtime percentage is then calculated as:

Weather Downtime (%) = (Time Waiting for Weather / Active Time) × 100

Important to Know

  • Weather downtime ranges from 0% to 100%
  • 0% means there was no weather downtime - perfect conditions!
  • 100% means there were no suitable weather windows at all during that period
  • The calculation only considers time when the logistics unit is supposed to be available according to your availability settings
Weather Downtime Metrics in Your Dashboard

When you view your simulation results, you'll see weather downtime presented in several different ways:

1. Weather Downtime per Logistics Unit

This chart shows weather downtime broken down by each vessel or equipment type in your simulation. You can view this data in three different time intervals:

Yearly View

  • Shows the accumulated weather downtime for each complete year of the simulation
  • Useful for understanding long-term patterns and annual variations
  • Displays the percentage of available hours lost to weather each year

Monthly View (Non-Aggregated)

  • Shows weather downtime for each individual month across all years
  • Helps identify specific months with weather challenges
  • For example, you might see that January 2028 had 45% weather downtime for your installation vessel
  • Displays actual calendar months as they occurred in the simulation timeline

Accumulated Monthly View

  • Aggregates the same months across all years to show typical monthly patterns
  • For instance, combines all January data to show that January typically has 38% weather downtime
  • Excellent for identifying seasonal trends and planning around challenging months

2. Weather Downtime Causes

This breakdown shows you what specific weather factors caused the most downtime for your operations. The system tracks which weather parameters (wind speed, wave height, etc.) prevented operations from proceeding.

For example, you might discover that:

  • 40% of downtime was caused by excessive wave height during foundation installation
  • 25% was due to wind speed during turbine lifting operations
  • 15% was due to tide conditions during jack-up operations

This information is invaluable for understanding where weather limits might be too conservative or where different equipment might help.

Weather Downtime in Your Output Report

When you download your Excel output report, you'll find detailed sheets with weather-related metrics:

Weather Downtime Sheet

Contains the raw weather downtime percentages for each logistics unit, broken down by time period. You'll see columns for:

  • Average - The mean weather downtime across all your simulation runs
  • P10, P20, P25, P30, P40, P50, P60, P70, P75, P80, P90 - These are percentile values showing the range of outcomes
    • P50 is the median - half of your simulation runs had higher downtime, half had lower
    • P90 represents a conservative estimate - 90% of simulation runs had lower downtime than this
    • P10 represents an optimistic estimate - only 10% of runs achieved this or better
  • Minimum & Maximum - The best and worst case scenarios from all your runs
  • Standard Deviation - Indicates how variable the weather downtime was across runs
  • Confidence Intervals - Statistical ranges that help you understand the reliability of the results

Net Weather Downtime Sheet

This sheet shows weather downtime calculated differently - it accounts for times when logistics units are scheduled to be idle anyway. This gives you a "net" impact of weather on your actual operations.

Key Difference: If a vessel was scheduled to be idle during a storm, standard weather downtime would count those hours, but net weather downtime would not, since the vessel wasn't planning to work anyway.

Understanding Weather Calendar

The Weather Downtime Calendar provides a more granular view of weather impacts by breaking down weather downtime for specific process steps.

What is Weather Calendar?

While standard Weather Downtime shows overall weather impacts per logistics unit, the Weather Calendar tracks weather downtime for individual operations such as:

  • Foundation installation
  • Turbine installation
  • Cable laying
  • Specific maintenance tasks

Technical Calculation Details

The Weather Calendar calculates downtime at the process step level by tracking:

  • Vessel - The logistics unit performing the step
  • Process - The parent process (e.g., "Foundation Installation")
  • Step - The specific operation within that process
  • Weather waiting time - Hours spent waiting for suitable weather conditions during that step

The calculation for each process step follows the same formula as overall weather downtime:

Step Weather Downtime (%) = (Hours Waiting for Weather on Step / Active Hours on Step) × 100

Active Hours on Step includes all time categories tracked during step execution, excluding:

  • LEADTIME - Time before the logistics unit is available
  • UNAVAILABLE - Scheduled unavailability periods
  • WAITING_TO_BE_SCHEDULED - Time before the simulation scheduler assigns work
  • OUTSIDE_AVAILABILITY - Time outside the unit's defined availability calendar
  • OUTSIDE_WORKSHIFT - Time outside defined working hours
  • NOT_SPOT_CHARTERED - Time when spot-chartered vessels aren't chartered

How Weather Calendar Data is Organized

The Weather Calendar sheet in your output report includes:

  • Vessel - The logistics unit performing the operation
  • Process - The high-level process (e.g., "Foundation Installation")
  • Step - The specific step within that process
  • Time breakdowns - Monthly, yearly, and accumulated statistics
  • All standard statistical metrics - Average, percentiles (P10-P90), min/max, etc.

When to Use Weather Calendar

Use the Weather Calendar when you need to:

  • Understand which specific operations are most affected by weather
  • Compare weather sensitivity between different installation methods
  • Optimize your process sequence to work around seasonal weather patterns
  • Identify bottleneck operations that are weather-constrained
Understanding Net Weather Calendar

The Net Weather Downtime Calendar is similar to the Weather Calendar but calculates weather impacts differently by filtering out non-productive waiting periods.

Technical Difference: Active Time vs. Net Active Time

Standard Weather Calendar includes all time when the vessel is actively engaged with a process step, including:

  • Time working on the step
  • Time waiting for weather to proceed with the step
  • Time waiting for other dependencies (other vessels, berth capacity, etc.)
  • All active operational periods

Net Weather Calendar only includes time when the step is:

  • Currently being worked on, OR
  • Actively waiting to be worked on (i.e., the step is next in queue)

What Makes it "Net"?

Net Weather Calendar excludes weather downtime during periods when the process step:

  • Is waiting for another vessel to complete prerequisite work
  • Another process step or process is active
  • Is waiting for berth capacity or port access
  • Is waiting for feeder vessel availability
  • Is waiting for storage capacity
  • Is on hold due to other project dependencies

Technical Implementation: The system filters out the following time categories from the active time denominator:

  • WAITING_TO_BE_SCHEDULED
  • WAITING_ON_GROUTING_VESSEL
  • WAITING_ON_FEEDER_VESSEL
  • WAITING_ON_BERTH_CAPACITY
  • WAITING_ON_STORAGE_CAPACITY
  • WAITING_ON_MAIN_VESSEL

This means if weather was bad while waiting for these dependencies, those hours don't count as "net" weather downtime since the step couldn't proceed anyway.

The Calculation Difference

Standard Weather Calendar Formula:

Weather Downtime % = (Weather Wait Time / All Active Time) × 100

Net Weather Calendar Formula:

Net Weather Downtime % = (Weather Wait Time / Net Active Time) × 100

Where Net Active Time excludes periods spent waiting for non-weather dependencies

When to Use Net Weather Calendar

Use Net Weather Calendar when you need to:

  • Understand the true weather impact on individual process steps
  • Calculate weather contingency for specific operations
  • Identify which operations genuinely need weather contingency vs. those constrained by other factors
  • Justify operational planning decisions (shows only the weather delays that matter)
  • Optimize process sequences to minimize weather-critical path time

Understanding Statistical Values (Percentiles)

The simulation runs multiple times with different weather year combinations to give you a range of possible outcomes. The percentile values help you understand this range:

  • Lower percentiles (P10-P30): More optimistic scenarios
  • Middle percentiles (P40-P60): Most likely outcomes
  • Higher percentiles (P70-P90): More conservative scenarios

For planning purposes, many users focus on P50 (the median outcome) and P75-P90 for conservative planning.

Tips for Using Weather Downtime Data

  1. Compare logistics units - Identify which vessels have the most weather downtime to optimize your fleet
  2. Look at seasonal patterns - Use the accumulated monthly view to identify the best and worst months for operations
  3. Review weather causes - Understand which weather parameters are the biggest constraints
  4. Consider percentiles - Use P75 or P90 for project planning to build in appropriate weather contingency
  5. Check yearly variations - See how weather downtime varies year by year to understand weather variability
  6. Use Weather Calendar for process optimization - Identify which operations are most weather-sensitive
  7. Focus on Net metrics for planning - Net Weather Downtime and Net Weather Calendar show the real project impact by filtering out periods where other constraints dominate

Choosing Between Standard and Net Metrics Common Questions

Q: Why do I see different weather downtime values in different reports?

A: Weather Downtime shows overall downtime, while Net Weather Downtime accounts for scheduled idle periods and dependency waits. Weather Calendar breaks down by process step. All perspectives are useful for different planning purposes.

Q: My weather downtime seems high. Is that normal?

A: Weather downtime varies greatly by location, season, and operation type. North Sea operations in winter typically have much higher weather downtime than summer operations in calmer seas. Compare your results against industry benchmarks for your location.

Q: How do the weather limits I set affect weather downtime?

A: Tighter weather limits (lower maximum wind speed, lower wave heights, etc.) will increase weather downtime. If you're seeing very high downtime, review whether your weather limits are realistic for your equipment and operations.

Q: What's the difference between Active Time and Available Hours?

A: Active Time refers to the hours when a logistics unit is actually engaged in operations (excluding periods like LEADTIME, WAITING_TO_BE_SCHEDULED, OUTSIDE_AVAILABILITY, etc.). It's a subset of Available Hours, focusing only on operationally relevant time.

Q: Should I use standard or net weather metrics for my project schedule?

A: For project timeline planning, use Net Weather Downtime and Net Weather Calendar as they show the actual impact on your schedule. Use standard metrics to understand total weather exposure and for logistics unit utilization planning.

Q: Why is the Weather Calendar broken down by process and step?

A: Different operations have different weather sensitivities and weather window requirements. Breaking it down helps you understand which specific activities are weather bottlenecks and may need special attention in your planning or different weather limits.

Q: When would Net Weather Calendar show significantly lower values than standard Weather Calendar?

A: When process steps frequently wait for other vessels or dependencies. For example, if a cable installation step waits for foundation installation to complete, and there's bad weather during that wait, the standard calendar counts it but the net calendar doesn't - because the cable work couldn't start anyway.

Need more help? Contact our support team for assistance interpreting your weather downtime results and optimizing your simulation setup.