Compass sextant

Types of Compass Sextant

A compass sextant is a navigational instrument that combines a compass and a sextant. It has a graduated arc or mirror for measuring angles and a circular box with a transparent top for holding the compass and a sighting telescope or a pair of sighting vanes. Depending on the design and use, a compass sextant can be categorized into different types. They include:

• Reflecting Compass Sextant

  The reflecting sextant has a unique design that uses an index mirror, a telescope, and a graduated arc to measure angles precisely. The index mirror reflects light and allows the observer to view both the observed object and the horizon simultaneously, enabling accurate angle measurement.

• Plastic Compass Sextant

  A plastic compass sextant is constructed from durable plastic materials. This makes it lightweight and rustproof. A plastic compass sextant is often used for educational purposes or recreational sailing since it is affordable.

• Electronic Compass Sextant

  An electronic compass sextant is a modernized version of the traditional compass sextant. It uses digital displays to show angles and measurements. The electronic compass sextant also has built-in sensors that provide real-time data and improve accuracy and convenience in navigation.

• Military Compass Sextant

  A military compass sextant is designed according to military specifications and standards. It is rugged, highly durable, and can be used in harsh environments. Additionally, the military compass sextant has advanced features such as night vision capabilities and electronic data integration.

• Harris Compass Sextant

  The Harris compass sextant is a specific type of compass sextant known for its precision and reliability. It is designed for maritime navigation, using high-quality materials and advanced engineering. The Harris compass sextant is suitable for professional sailors and navigators and boasts a reputation for excellence in navigation.

• Plastic Compass Sextant

  A plastic compass sextant is constructed from durable plastic materials. This makes it lightweight and rustproof. A plastic compass sextant is often used for educational purposes or recreational sailing since it is affordable.

Specifications and Maintenance of Compass Sextant

Compass sextants have different specifications depending on the type and use. Here are some general ones:

• Optical System

  It includes a telescope with a powerful lens and an efficient light-gathering system. The index glass and the horizon glass have specific spacings that minimize parallax errors. Furthermore, the sextant's arc and frame have coatings that reduce light reflections, ensuring clear observations.

• Construction Material

  Typically, sextants are made from aluminum or brass, being lightweight and corrosion-resistant. They are essential for marine environments where rust and corrosion can occur. Additionally, the sextant's frame and arc are made of durable materials to withstand rough conditions.

• Index Mirror

  This is a critical component of a compass sextant, where the size and quality determine the sextant's accuracy. The index mirror is coated with a thin layer of silver or aluminum, which provides a precise reflection. Furthermore, it is manufactured to be free of distortions and should be regularly polished to ensure optimal performance.

• Scale and Graduation

  Compass sextants are equipped with arcs and scales that allow users to measure angles with precision. The graduation is designed to be clear and easy to read, ensuring accurate observations. Depending on the type, the graduation range may vary, with some models having a larger range.

• Adjustment Mechanisms

  Various compass sextants have different adjustment mechanisms, ensuring users can make precise measurements. These mechanisms include tangent screws, micrometers, and clamp screws, enabling users to adjust the index and hold it securely.

• Weight and Size

  Depending on the model and manufacturer, compass sextants come in various sizes and weights. Portable and lightweight sextants are more convenient for on-deck use and navigation, while larger and heavier sextants are more accurate but less portable.

Regular maintenance is essential for sextant accuracy and durability. Here are some general maintenance tips:

• Cleaning: Clean all sextant parts, especially the optical system, the index mirror, and the mirrors, regularly. Use a soft cloth and mild cleaning solution to avoid scratches or damages.
• Calibration: For accurate measurements, calibrate the sextant regularly. Adjust and align the index mirror and other components as needed.
• Optical Care: To prevent dust, fingerprints, or smudges on the lenses, use a microfiber cloth or lens cleaning solution. For stubborn dirt or debris, use a lens brush or blower.
• Storage: When not in use, store the sextant in a dry and clean place, away from extreme temperatures and humidity. Use a protective case or cover to prevent damages.
• Mechanical Parts: These include the frame, index arm, and micrometer screw. Ensure they are free from rust and corrosion. Apply a few drops of oil to reduce friction and ensure smooth movement.

How to choose a compass sextant

There are several factors to consider when choosing a compass sextant, such as the purpose, user experience, and different types of sextants.

Consider the purpose of the compass sextant when choosing one. Is it for educational purposes, navigational backup, or actual maritime navigation? If it's for education, a plastic or less expensive model may be suitable. For navigational backup, consider a sturdy and reliable sextant. For actual maritime navigation, a high-quality, durable, and precise compass sextant is essential.

Another factor to consider is the user experience. Think about the user experience and skill level of the person using the compass sextant. If it's for a child or beginner, choose a simpler and more straightforward model. Experienced users can handle more complex and advanced features.

The different types of sextants also play a key role in selecting the right compass sextant. There are various compass sextants available, such as the traditional metal sextant, plastic sextant, and electronic sextant. The traditional metal sextant is durable and long-lasting but requires more maintenance. A plastic sextant is affordable and low maintenance but less accurate and durable. An electronic sextant is more expensive but offers advanced features and high accuracy.

Ultimately, choosing a compass sextant depends on budget, maintenance requirements, and accuracy needs. Consider the budget, maintenance, and accuracy requirements before choosing a compass sextant that suits the needs of the users.

How to DIY and replace compass sextants

As mentioned earlier, it is very hard to find a sextant in a regular bookstore. However, there are other options that provide users with a compass sextant for DIY purposes.

• Online retailers: Websites like Amazon may offer a compass sextant. Users should research the options available and see if it meets their needs.
• Specialty nautical supply stores: These are physical stores that specialize in selling nautical equipment for navigation and boating. They might have a few sextant models.
• Used sextants: For a more affordable option, users can consider shopping for second-hand sextants. However, your sextant needs to be in good condition and function properly to provide accurate measurements. This might be hard to tell just by looking at it. Therefore, users might need professional advice to determine whether a used sextant is viable.
• Local marine services: These are service providers that maintain and repair marine equipment. They might have a few sextants or be able to order one for the user.

Q and A

Q: Can one still use a sextant if the index error is not corrected?

A: Yes, but the measurements will be inaccurate. The index error is a systematic error that can affect all measurements in one direction (e.g., always too high or too low). If the index error is not corrected, the sextant will give consistently erroneous readings, so the navigator will know the error but not the direction (± or -) of the error.

Q: Why is the sextant an important instrument for navigation?

A: The sextant is important for navigation because, with it, one can measure the angle between the moon, a star, or the sun and the horizon. This angular measurement allows navigators to determine their latitude and longitude, providing a precise location.

Q: Does one need a sextant to navigate in the modern world?

A: No, it is not necessary to have a sextant to navigate. Electronic devices like GPS provide precise location information. However, knowledge of sextant use and celestial navigation principles can be valuable, especially in areas where technology may fail.

Q: Can one use a sextant at any time of the day?

A: Yes, a sextant can be used at any time of the day, but during the night, stars are the only reference available. Measurements can be taken, but they require more calculations due to the varying brightness and fewer reference stars.