Spanish and English Maritime Distance Measurements

Due to various inconsistencies of 16th century measurements, understanding distances given by 16th century mariners can be somewhat confusing. And, considering the limitations of period methods for determining distances, complications increase. Nevertheless, the accounts of Sebastian Cermeño, Sebastian Vizcaino, and Sir Francis Drake—mariners all at Drakes Bay—record distances that are usually close to actuality.

return to maritme background

In the hands of a skilled navigator, the cross-staff could satisfactorily provide latitude location.

Wikimedia Commons Image

Marine League

Long distances of maritime travel were typically stated in leagues. Fundamental to the period application and understanding of a league was the distance represented by one degree of a meridian encircling the Earth, and this degree of distance was based on the value of the Earth’s circumference. While in the 1500s there were various determinations of the Earth’s circumference value, none were universally accepted. Two, however, carried the greatest influence for Spanish and English seamen—those by Eratosthenes (276 BC–ca. 195 BC) and Claudius Ptolemy (ca. 100–ca. 170). These mathematician-geographer-astronomers calculated different distances, Eratosthenes one very close to reality and Ptolemy one that was much shorter than reality. Both guided maritime efforts.

Wikimedia Commons Image

Eratosthenes and Ptolemy used a common unit to the time, the stadion which was based on the distance around a sport stadium. Spanish and Portuguese seamen used one Roman mile as equivalent to 10 stadia. The commonly accepted distance for a Roman mile at the time is equivalent to our modern distance of 5,000 feet.

As the 15th century closed, the Spanish and Portuguese mariners based their measurements on the calculations of Eratosthenes. He judged the Earths’ circumference to be 252,000 stadia which is 25,200 Roman miles. With this, mariners determined one degree of latitude equaled 70 Roman miles and they applied the distance of four Roman miles to represent one league. Using this, it took 17.5 leagues to cover one degree of latitude.

However, as political and economic rivalries developed regarding their relentless pursuit of wealth, Spain and Portugal argued over what constituted equal hemispheres of influence. Consequently, distance values were affected while manipulated numbers created favorable geographic assertions. In order to bring the Moluccas—the fabled spice islands—into their economic sphere, the Spaniards adopted Ptolemy’s determination of circumference: 180,000 stadia. With this, one degree of latitude equaled 50 Roman miles and they applied the distance of three Roman miles to represent one league. Using this, it took 16.666 leagues to cover one degree of latitude. But this was temporary, and around 1600, they reverted back to the value of four Roman miles to one league.

In the second half of the 1500s, the English deemed one degree of latitude equaled 60 Roman miles and they reckoned the distance of three Roman miles to represent one league. With this, it took 20 leagues to cover one degree of latitude. This is the value used by Drake.

This 60 mile value exists across the world today but not in the Roman mile distance. As the true circumference of the earth was eventually determined, the nautical mile was developed. It is comprised of 6076.12 feet. One minute of one degree of the circle of the Earth makes one nautical mile and corresponds to one minute of latitude. This is somewhat longer than the statute (land) mile of 5,280 feet. This makes the modern league approximately 3,228 feet longer than the Elizabethan league.

Raymond Aker calculated that Cermeño used the value of three Roman miles to a league on his ill-fated journey that left his ship at the bottom of Drakes Bay in 1595. Aker determined Cermeño’s measurement of one league to be roughly equivalent to 2.3 nautical miles. The pilots of the Vizcaino expedition used the value of four Roman miles to a league on their 1602-1603 expedition which took them to Drakes Bay in January of 1603.

Land League

Cermeño also used league units when stating land distances. None of the accounts regarding the Cermeño expedition distinguishes between land and marine leagues. However, distances Cermeño used on land are much shorter than those at sea. Using the Cermeño accounts of descriptive measures and converting them to modern units, Aker was able to correlate other details of Cermeño’s inland journeys—and these indicate a shorter distance for land leagues than marine leagues. In the end, Aker states Cermeño’s land league to be approximately equal to 1.36 modern statute miles. Aker believed the land league to be the use of an archaic measurement, the legua, which was equal to 1.5 Roman miles.

Other distances

At times, records show distances measure using units of musket-shot and harquebus-shot. These distances are difficult to determine with precision. In addition to a lack of general agreement as to the range of these weapons, we do not know if the distance referred to extreme range (the distance one would expect an unimpeded projectile to ultimately come to rest) or maximum effective range (the distance one could expect to inflict significant harm to an enemy). Aker cautiously proposed distances since they are approximations and uncertain. He believed they may err on the short side. However, they are useful as a reader can glean a rough distance when read in context.

Aker stated the musket-shot distance to be approximately 1,450 feet and the harquebus shot to be approximately 500 feet.

Depth

The only 16th century expedition to record depth at Drakes Bay was the Cermeño expedition. Cermeño measured the entrance to Drakes Estero using the unit braza which is the Spanish unit for the modern fathom. One braza is equal to 5.492 modern feet. Another way to think of this is that a braza is 91% of a modern six foot fathom.

Watch this video to learn about nautical miles.

Spanish and English Maritime Distance Measurements

Navigating the History of New Albion

Site Map