Abel Tasman - How did they navigate?Abel Tasman - How did they navigate? 

Heemskerck was the flagship on Abel Tasman’s 1642 voyage. It was a war ship that carried cannons. We do not know exactly what it looked like, but sketches by the voyage’s artist, Isaac Gilsemans, some written records and other VOC ship designs, have helped historians make a good guess.

[icon:book] A flagship is the vessel captained by the commanding officer on a sailing voyage.

Zeehaen was Abel Tasman’s other ship on the 1642 voyage. It was a Dutch tall ship called a fluyt, built mainly to carry cargo instead of lots of weapons. You can think of Zeehaen as the helpful supply ship, sailing alongside Heemskerck and supporting the crew on their long ocean voyage.

[icon] A compass is a navigation instrument used to find direction. Compasses contain a magnetic needle that aligns with Earth’s magnetic field. Tasman would have used one to find north, south, east and west.

A compass showing the cardinal points (north, east, south and west) and the intermediary points (north-east, south-east, south-west and north-west) ANMM Collection. Object Number 00006653

Tasman may have used a backstaff to determine his latitude. This was a technological improvement on the cross-staff. 

[icon] A backstaff was a historical navigation instrument used by European navigators to work out their latitude. The angle between the sun and the horizon was measured using shadows. It was safer than a cross-staff because the person using it kept their back to the sun, which protected their eyes from the direct sunlight.

A photograph of a backstaff use to measure latitude

A backstaff from the mid 18th century. ANMM Collection. Object Number 00040037.

Tasman could work out his latitude fairly accurately, but longitude was still a challenge. That made sailing across open oceans much harder than sailing near land, where he could follow the coastline.

To work out where they were, Tasman’s crew would have used a number of methods which are combined to form dead reckoning.

[icon] Dead reckoning was a way mariners estimated the location of their ship in the open ocean. They started from a place they already knew, then made a careful guess about their new position each day by using the ship’s speed, direction and the time they had travelled.

They checked the ship’s direction with a compass and measured speed with a log line.

[icon] A log line was a device used to calculate the speed of a ship. It consisted of a wooden board attached to the end of a long rope with evenly spaced knots tied in it. It was dropped behind the ship while a sandglass timed how quickly the knots slipped past.

A photograph of a log line used to measure the speed of a ship

Log line. ANMM Collection. Object Number EN000134

Every half hour, the crew recorded the ship’s speed and direction on a traverse board. It was a clever system, but not perfect. Ocean currents, storms, inaccurate measurements or simple mistakes could push a ship far away from where the sailors thought they were. You can find a 3D scan of a traverse board in the 'Bonus content' chapter!

Tasman’s crew often checked the ocean’s depth using a lead line. 

[icon] A lead line was a tool sailors used to measure the depth of the ocean. It is a long rope with a heavy lead weight tied to one end. Sailors dropped it over the side of the ship to take a sounding. This helped ships avoid hidden dangers like coral reefs, rocks or a shallow seafloor. 

A photograph of a lead line used to measure the depth of the ocean

A 20th century lead line used for determining the depth of water for safe navigation, consisting of a length of rope with bell-shaped piece of lead attached to the end via a leather loop, with various pieces of coloured cloth, knotted string, wooden toggles and fringed leather attached at various lengths along the rope. ANMM Collection. Object Number 00047439