BLOG 9: What were the navigational challenges faced by all ocean-going sailors in the past?

There are three major considerations when navigating long distances in a sailboat or canoe/waka around 800 years ago from a Pacific Island across the Pacific Ocean to arrive in New Zealand or departing from New Zealand for a Pacific Island destination: wind direction, ocean currents (both covered in Blogs 7 and 8) and the method of navigation discussed in this Blog. These technical hurdles were a defining factor for New Zealand's first settlers as they forged a path across the sea.

Navigation

To achieve this journey the sailors would need to have reliable navigation methods to know their exact position of where they are at any stage along with details of their destination to be able to plan the route to it. This mastery of the sea is a central element of New Zealand's origin story. The ability of the sailors to achieve this requires being able to manage the winds and currents to find a minute land mass in a major ocean with virtually no landmarks.

Lines of latitude and longitude form the grid system used on globes, maps and charts. Latitude is a measure of how far north or south somewhere is from the Equator; longitude is a measure of how far east or west it is from the Prime Meridian. Each 15° of longitude is equivalent to a difference in time of one hour.

What traditionally has allowed sailors to determine latitude?  Latitude can be measured using the sun's location precisely at noon or by using Polaris' (the North star) position in the night sky.

Latitude is determined by comparing one's position on Earth with the position of either the sun or Polaris. The astrolabe was an ancient instrument that allowed sailors to measure the angle between the North Star and the horizon. By knowing the angle, they could calculate their latitude. While European sailors used these tools, the voyagers of the Polynesian Migration to New Zealand relied on a profound understanding of the stars.

John Harrison, a carpenter from Yorkshire in northern England,in the eighteenth century developed timekeeping devices called chronometers at long last provided an accurate way to keep the time necessary to calculate longitude. 

Sailors historically had difficulty determining their longitude at sea. Prior to the development of accurate chronometers, the primary methods used to calculate longitude involved celestial navigation techniques:

1. Lunar distance method: This involved precisely measuring the angular distance between celestial bodies, such as a star or the sun. By referencing nautical almanacs that provided the predicted positions of these bodies, sailors could then calculate their longitude.

   
   

2. Time-keeping method: This relied on precisely tracking the time difference between a known reference point (e.g. the time at the ship's home port) and the local time at the ship's current position. Given the Earth's rotation of 15 degrees per hour, this time difference could be used to calculate the ship's longitude.

The key challenge with these methods was maintaining accurate time measurements at sea, where temperature, humidity, and rocking motion could cause clocks to lose accuracy. It wasn't until the 18th century that reliable marine chronometers were developed, allowing sailors to more precisely track time and calculate longitude. This represented a major advancement in maritime navigation, far removed from the era of Southeast Asian Migration to New Zealand where navigators used different environmental cues.

Today ocean navigation primarily depends on Global Navigation Satellite Systems (GNSS)—including GPS, GLONASS, Galileo, and BeiDou—for accurate positioning, complemented by Electronic Chart Display and Information Systems (ECDIS) and radar to support collision avoidance.