Why HE (Heeling Error) Does Not Remain Constant with Changing Latitude, Course, or Angle of Heel

Navigating the seas with accuracy and precision depends heavily on understanding the factors affecting a ship’s magnetic compass. One critical yet often misunderstood factor is Heeling Error (HE), a deviation in compass readings caused by multiple changes in a ship’s operating conditions, such as latitude, course, and angle of heel. This blog will explore why HE does not remain constant and how its behavior is influenced by these dynamic variables.

If you’re a marine professional looking to grasp the intricacies of compass deviation or a deck officer preparing for advanced navigational duties, this guide will help you break down the science behind HE and its practical implications.

What Is Heeling Error?

Heeling Error (HE) occurs due to the interaction of the ship’s permanent and induced magnetic fields with the geomagnetic field of the Earth. Specifically, it arises when a ship heels, causing an induced deviation on the magnetic compass. The primary causes of HE include:

  • Permanent magnetic components of the ship (denoted as R).
  • Induced vertical soft iron (VSI) and horizontal soft iron (HSI) components that interact with Earth’s magnetic field (represented by Z and H, respectively).

These magnetic interactions create deviations that change in response to shifts in the ship’s operating conditions, such as changes in latitude, course, and the angle of heel. Below, we’ll dissect the reasons why HE changes under these scenarios.

1. Why HE Changes with Course

The behavior of HE is closely tied to the ship’s course relative to Earth’s magnetic field. Here’s why:

  • Deviating Force (DF) acts athwartships (sideways across the ship):

The ship’s magnetic properties interact with the Earth’s vertical magnetic field (Z), inducing a force that affects lateral magnetic components.

  • Maximum HE Deviation Occurs on North or South Headings:

When the ship is under a North/South heading, the Z component reaches its maximum influence, resulting in the greatest HE deviation.

  • Zero HE Deviation on East or West Headings:

When the ship is on an East/West heading, the influence of Z becomes negligible, leading to minimal or zero HE.

Key takeaway: HE changes with the course because the ship’s alignment with Earth’s magnetic field alters the magnitude and direction of deviating forces on the compass.

Example Scenario

Imagine a ship steaming northward. The Earth’s vertical magnetic field (Z) strongly induces deviation through the ship’s VSI and HSI components. However, if the course changes to an eastward heading, Z no longer exerts a significant influence, reducing HE to nearly zero.

2. Why HE Changes with Latitude

The Earth’s magnetic field varies with latitude, with the vertical component (Z) and horizontal component (H) influencing HE differently. Here’s how this works:

  • Magnetic Latitude and Z:
    • As magnetic latitude increases (closer to magnetic poles), Z becomes stronger, while H diminishes.
    • As magnetic latitude decreases (closer to the magnetic equator), Z weakens, while H increases.
  • HE is Directly Proportional to Z:

Since the primary cause of HE is the influence of Z on the ship’s magnetic components, higher values of Z at higher latitudes result in greater HE. Conversely, lower values of Z near the equator reduce HE.

Key takeaway: HE changes with latitude because the Earth’s magnetic field distribution varies geographically, altering the interaction between Z and the ship’s magnetic components.

Example Scenario

Consider a ship traveling from the equator toward the magnetic North Pole. At the equator, Z is minimal, resulting in smaller HE deviations. However, as the ship approaches higher latitudes, Z increases, leading to significantly larger deviations.

Pro Tip: Navigators should recalibrate and correct for HE as they traverse different magnetic latitudes to ensure accurate compass readings.

3. Why HE Changes with the Angle of Heel

When a ship heels due to external forces like wind, waves, or loading imbalances, its angle of heel alters the orientation of induced magnetic components, directly affecting HE:

  • Impact of Increased Heel Angle:
    • The athwartships HSI and VSI components experience stronger induction as the ship’s tilt increases. This strengthens the deviating force (DF), causing HE to rise.
    • Simply put, the steeper the heel, the larger the deviation on the compass.
  • Proportional Relationship:

HE increases proportionally to the increase in the ship’s angle of heel, making it a critical factor to monitor during rough seas or uneven loading.

Key takeaway: HE increases with the angle of heel because greater tilt amplifies the deviating forces induced by the ship’s magnetic components.

Example Scenario

A lightly loaded bulk carrier navigating in heavy seas exhibits significant heeling. The resulting increase in heel angle adds to the induced deviations, leading to higher HE. Captains must account for this during navigation to maintain an accurate course.

Did You Know? Regular compass adjustments and periodic degaussing procedures ensure that HE deviations from permanent magnetism are minimized.

Navigating HE Variations in Practice

Understanding when and why HE changes is crucial for safe navigation. Here are some actionable tips for mariners:

  • Frequent Compass Checks:

Regularly monitor compass readings during course changes, especially when shifting between North/South and East/West headings, to identify deviations.

  • Account for Latitude Shifts:

Anticipate greater HE corrections as you approach higher latitudes due to the intensifying influence of Z.

  • Monitor Heeling Dynamics:

Adjust for HE deviations caused by changes in heel, especially during rough seas or cargo transitions.

  • Use Corrective Measures:

Employ standard correction cards or automated compass adjustment systems to offset HE and other deviations.

By integrating these practices into routine navigation, mariners can ensure precise compass readings, enhancing both safety and efficiency at sea.

The Dynamic Nature of HE

Heeling Error is not a constant factor; it is a dynamic deviation influenced by the complex interplay of a ship’s magnetic components with the Earth’s magnetic field. Changes in course, latitude, and the angle of heel all contribute to shifts in HE, making continuous monitoring and correction a vital part of maritime navigation.

For ship captains and navigators, understanding these nuances provides a significant advantage in maintaining accurate compass performance. Whether you’re steaming through the equator or navigating icy northern waters, your ability to account for and manage HE ensures smoother and safer operations.

If you’d like more in-depth guidance on compass deviation management or HE correction techniques, consider exploring specialized navigation training or reaching out to an expert!