How Can I Decrease My Alpha Factor Margin?

There are many pieces of information that are collected when planning a marine operation, from the risk assessment to its alpha factor. These practices are in place to ensure that any process is done safely and that the equipment and crew are protected from unsafe weather conditions.

The consequences of weather conditions on a marine operation can range from monetary loss to environmental pollution. In addition, there have been consequences ranging from minor injuries to the loss of lives.

With DTN EPS Long Range Forecasts, long-range forecasts help planning and decision making by supporting risk management and illustrating the confidence of the forecast for a longer period. 

This article defines what an alpha factor is, how it is calculated, and how to conduct your marine operations safely. As well, learn more about how DTN can improve your alpha factor increasing operability while also maximizing safety.


Risk Assessment in Marine Operations

You must adequately assess the risk involved when operating at sea. The DNV requires that a risk assessment accompany all marine operations for safety purposes. This assessment is used to determine whether or not there is an acceptable level of alpha factor margin available before beginning their marine operations offshore.

Operations are divided between “weather restricted” and “unrestricted” operations. The environmental criteria for weather unrestricted operations are based on extreme value statistics because the task is supposed to be done in all but extreme weather conditions. Therefore, your crew must be able to do the design and operation in such a way that all but extreme conditions are acceptable.

The criteria for weather-restricted operations are selected by the owner based upon different conditions. Those conditions include parameters set by the insurance company, how long the wait will be for suitable weather, and those associated costs.

Whether a maritime project is considered weather restricted or unrestricted depends on the length of the weather window.

Offshore Platform

Calculating Weather Windows

The weather window refers to the period that it is safe to conduct an operation. This means that the weather forecast indicates that it is safe for your marine operation or offshore construction to take place, given the maximum threshold your project has for window, wave height, etc. The waves need to be lower than whatever maximum wave height is determined as acceptable for your project for the entirety of that project.

Calculating your weather windows can be a challenge, as the weather can be more unpredictable with time. That is taken into account when calculating your weather window. Generally speaking, the further out the window, the less accurate it is.

The operation period (referred to as TR by the DNV) is calculated by combining the estimated operation time with the estimated unforeseen time. For example, a weather-restricted operation has an operation time of fewer than 72 hours. Once you have calculated your operation period, you can then calculate your alpha factor.


Calculating Your Alpha Factor

The alpha factor is the ratio between the design criterion and the operational criterion. So let’s define those two terms.

The design criterion is the maximum wave height that is permissible for your activities to happen safely.

The DNV has created a set of guidelines for calculating your alpha factor margin. Below is an example of a situation where there is no environmental monitoring:

LRDF with no environmental monitoring

So, let’s use an example. Imagine your team has determined that for your project, your maximum acceptable wave height is 2 meters.

For a planned operation that would last for less than 12 hours, you would multiply the 2 meters by 0.84. Your operational criterion, meaning the maximum height you could now perform your activities, is 1.68 meters.

This process has dramatically reduced the maximum wave height in which you can perform your operations.

However, when there are environmental monitoring processes in place, notice how the alpha factor calculation changes:

LRFD with Environmental Monitoring

By having environmental monitoring, whether that is an onboard meteorologist, weather forecasting services, or marine sensors aboard your vessel, the level of uncertainty is reduced. Therefore, you can better know if it is safe to work, which is why the alpha factor margin is reduced.

Ship in rough waters

Reducing Your Alpha Factor Margin

The alpha factor calculation is not the only criteria you must consider when determining your allowable weather window, but it can be most important. You can open up a more significant number of potential days for operations within an acceptable wave height range by reducing your alpha factor margin!

You will reduce your alpha factor depending on the type of weather forecasting, sensors, and meteorological insight involved with your project. Tackling alpha factor reduction is often a multistep process. It may involve:

  • closer monitoring and tracking of environmental conditions;
  • the employment of an onboard meteorologist (or similar);
  • outputs from weather and wave forecasting services

The alpha factor margin exists to combat uncertainty in weather forecasting. So, it logically stands to reason that the more accurate a weather forecast, the less that you would need to rely upon your alpha factor margin.

In fact, that is one common complaint of the alpha factor margin calculation. It assumes that the quality of environmental monitoring is the same across the board. That is simply not true.

With data modeling and advancements in technology, weather forecasting can now help you better anticipate anticipated conditions and determine the forecast confidence level over a given period. 

Cargo ship. sailing in fog

Better Manage Your Risks with Better Weather Forecasting

DTN’s Ensemble Prediction System (EPS) Long-Range Forecasts are based on a collection of 50 model runs compared with the operational forecast baseline generated from several high-resolution model runs. When used with your daily marine weather reports, the probability-based EPS Long-Range Forecasts help you target future working weather windows and have confidence in those predictions.

Our EPS Long-Range Forecasts provide valuable insights in a graphical format for the following parameters over a 15-day outlook period:

  • Wind Speed
  • Significant Wave Height
  • Wind Direction
  • Temperature (optional)
  • Precipitation (optional)
  • Clouds (optional)
  • Swell Wave Height (optional)

An experienced meteorologist will also prepare a detailed, synoptic outlook to evaluate the forecast confidence based on the weather intelligence in the long-range forecast.

Knowing what weather you face is not enough. What you need is operational intelligence. With DTN’s long-range forecasting, you will have the lead time that you need to plan your operations and manage your risk.

For example, consider the below charts from the DNV. By using EPS Long-Range Forecasts for a high-risk operation that is <12 hours, your alpha factor margin improves significantly – from 0.75 to 0.85.

Alpha Factors for Waves

Make better long-range decisions for more long-range success with DTN.