US Survey Feet (ft-us) to Fathoms (fathom) conversion

What is us survey feet?

What is US Survey Feet?

US Survey Feet is a unit of length used in the United States for land surveying. It is slightly different from the international foot. Understanding its origin and applications is crucial for accurate land measurements and legal descriptions.

Origin and Definition

The US Survey Foot (ftUS) is defined based on the Mendenhall Order of 1893, which related customary units to the metric system using the meter. At that time, it was defined as:

1 US Survey Foot = $\frac{3937}{1200}$ meters

This value equates to approximately 0.3048006096 meters. This differs slightly from the international foot which is exactly 0.3048 meters. The difference, while seemingly small (2 parts per million), can accumulate significantly over large distances, impacting land boundaries and area calculations.

The Issue & Readjustment

The difference between the international foot and the US survey foot caused discrepancies, especially in states that relied heavily on the Public Land Survey System (PLSS). Over time, states have addressed this issue in various ways:

• Many states have officially adopted the international foot for all new surveys.
• Some states continue to use the US Survey Foot. It's crucial to know which definition is in use for any particular survey or land description.
• Conversion factors are often provided in legal documents to clarify which foot is being used.

For more information about each state's definitions of feet, please read NOAA's definition of US Survey foot.

Usage and Real-World Examples

While its use is declining, the US Survey Foot is still relevant in some contexts, especially when dealing with older surveys and legal descriptions. Understanding its magnitude helps grasp spatial relationships:

• Property Boundaries: In states where it is still used, a land description stating a lot is 100 US Survey Feet wide means it is approximately 30.48006096 meters wide.
• Land Area Calculations: Area calculations, like acres, derived from measurements in US Survey Feet will differ slightly from those derived from international feet.
• Geographic Information Systems (GIS): GIS databases may contain data referenced to US Survey Feet, requiring proper transformation when integrating with data using the international foot.

Interesting Facts

• The slight difference between the two definitions of a foot has caused legal disputes related to property boundaries.
• The National Geodetic Survey (NGS) provides tools and resources for converting between the US Survey Foot and the international foot.

What is Fathoms?

Fathoms are a unit of length primarily used for measuring water depth. Understanding its origin and applications provides valuable context for maritime and historical studies.

Definition of Fathom

A fathom is a unit of length equal to six feet (approximately 1.8288 meters). It's primarily used in maritime contexts to measure the depth of water. The symbol for fathom is fm.

Origin and History

The term "fathom" originates from the Old English word "fæthm," which meant the distance between the fingertips of two outstretched arms. This roughly corresponds to six feet. Historically, it was a practical way for sailors to measure depth before sophisticated instruments were available.

How is a Fathom Formed?

The length of a fathom is based on the average span of a man's outstretched arms. While not precisely defined by any single individual's measurement, it represents a practical approximation.

$$1 \text{ fathom} = 6 \text{ feet} = 1.8288 \text{ meters}$$

Interesting Facts and Historical Significance

• Nautical Charts: Fathoms are commonly used on nautical charts to indicate water depth.
• Treasure Island: Robert Louis Stevenson's "Treasure Island" references fathoms in describing depths where treasure is buried.
• Submarines: Depth ratings for submarines are often expressed in feet, which can be easily converted to fathoms for quick reference.

Real-World Examples

• Sounding the Depth: In older nautical texts, you'll often read about "sounding the depth," where a weighted line marked in fathoms is dropped to the seabed to determine the water's depth.
• Modern Nautical Charts: Today's nautical charts use fathoms and feet to provide precise depth information for navigation. For example, a chart might indicate a depth of "10 fathoms 3 feet," meaning 63 feet.
• Titanic's Resting Place: The wreck of the Titanic lies at a depth of approximately 1,250 fathoms (around 12,500 feet).

Conversion Examples

• Fathoms to Feet: 5 fathoms = 5 * 6 feet = 30 feet
• Fathoms to Meters: 10 fathoms = 10 * 1.8288 meters = 18.288 meters
• Feet to Fathoms: 24 feet = 24 / 6 fathoms = 4 fathoms

Additional Resources

For a deeper dive into the history and usage of fathoms, consult the following resources:

• National Ocean Service (NOAA) - Provides information on nautical charts and depth measurements.
• Wikipedia - General information about Fathom.