What Is The Longest Straight Line Sea Route?

Sea freight involves travelling with huge amounts of cargo across vast distances to destinations all over the world. The sheer scale of operations to take freight to Russia, or Australia or the United States is phenomenal.

However, what would be the theoretical longest straight-line shipping route in the world? A range of physicists, engineers and geographers spent years trying to work out what the longest straight-line journey around the world would be and the result is somewhat surprising.

The Question

The problem, as posited in Science Magazine, works like this; if you went on a boat journey without a rudder, what would be the longest possible journey? Due to the curvature of the Earth, it was a question that was surprisingly difficult to answer.

On land, the longest possible journey you can take in a straight line goes from Sagres, at the extreme end of Portugal to Jinjiang, on the East coast of China, a distance of 11,241km (6985 miles).

At sea, the question is somewhat trickier, and getting proof of the answer required elaborate modelling and research from some of the most intelligent computer engineers in the world.

The Theory

There are three theoretical longest routes around the world that are longer than halfway around the world (known as the antipode), which is measured at 19,840km (12,330 miles).

The first route, which measures over 20,000km goes from Invercargill in New Zealand, off the coast of Brazil and finally stopping on the southwest coast of Ireland.

The next route reaches over 25,000km and travels from Hormozan province in Iran, and finally ends up on the southwest coast of Mexico.

The final and most compelling route reaches 32,040km (19,910 miles) and goes from Sonmiani, near the port of Karachi in Pakistan, across the Arabian Sea, around both the bottom of South Africa and the bottom of Argentina and Chile, eventually landing in the Karingshy District of East Russia.

The Proof

Proving the theory proved to be the most difficult task, and required the use of data from the National Oceanic and Atmospheric Administration, which provided a scale model of the earth which had a spatial resolution of 1.8 kilometres.

After this, it was a matter of calculating the great circle, a straight-line path across a sphere. Brute forcing the answer with a supercomputer was out of the question because they needed to check 5,038,848,000,000 points on the map to ensure they were not on land: an impossible task.

They used a dedicated algorithm which fine-tuned the search over and over for the most promising lines, and the results proved that the final route was indeed the longest possible straight line across the seas. On flat maps, it looks curved, but when modelled onto a sphere it is completely straight.

One complication with the study however is that the Earth is not quite a perfect sphere. It is an oblate spheroid, which means that it is slightly wider at the equator and slightly flatter at the poles due to gravity.