Google and Facebook lay thousands of miles of undersea cables to ferry internet around the world. Here’s how they do it.

Google and Facebook have both laid thousands of miles of cables along the seafloor, stretching between continents, to carry internet around the world.

Often, the two tech giants invest in cable projects along with a consortium of other companies, although Google has five privately owned cable projects underway.

In total, Google is invested in 19 cable projects around the world.

Facebook is invested in two cables that are currently active. It is involved in five more cable projects currently under construction, a spokesman said.

Here’s how the companies lay the cables along the bottom of the ocean.

First, the companies have to plan the route they want the cable to take.

Jayne Stowell, strategic negotiator for Global Infrastructure at Google, told Insider planning the route can take up to a year.

A Facebook spokesperson told Insider it conducts a bathymetric and geophysical survey along its expected route, which allows it to plan down to the meter.

To do this, it sends out vessels equipped with sonar to map out the seabed and look for risks such as high currents, underwater landslides, and unexploded bombs or mines.

The cable itself is about the thickness of a garden hose, Stowell said.

Cables are wrapped in a copper casing for electricity conduction.

“A plastic and steel sheathing is then added to waterproof the cable and help it withstand potentially adverse ocean conditions such as heavy currents, earthquakes or interference from fishing trawlers,” Stowell said.

For Facebook’s 2Africa cable, it’s using aluminium rather than copper, which it said will lower manufacturing costs and enable longer cables.

2Africa is in the process of being laid around the entire continent and is 37,000 kilometers long — only slightly shorter than the circumference of the Earth.

Once the route is mapped out and the cable is made, it’s time to load the cable onto a specialised laying vessel.

Google’s Stowell said the company uses a fleet of 50 to 55 specialised laying vessels, with capacity for up to 100 crew members. Just loading the cable onto the ship can take four weeks, she said.

Facebook said its vessels generally need a crew of 30 to 50 people.

The vessel leaves port, spooling the cable behind it. Once it gets into deeper water, it deploys an underwater plow to dig a trench along the seabed into which it lays the cable.

“The natural movement of wave action will then cover the cable once the ship moves on,” Stowell said.

“An ocean plough does not look too different from a plow a farmer might use in a field, except it is much larger – about the height of a two-story building,” Stowell said.

The plow is only used at depths of 1,000 to 1,500 meters (3281 to 4921 feet), Stowell added.

“This is where it is needed to protect the cable from potential damage from other seabed users – most frequently bottom trawling fishing vessels or ships anchors that are put down at sea in a storm,” Stowell said.

A cable is fairly safe in the deep seas and has no need for burial nor armoring, she added.

For longer cables, Stowell said Google also installs a device called an amplifier every 100 meters (328 feet) to boost the signal and keep the data moving.

“Although fibre-optic cables are made of the purest glass, over long distances the intensity of a beam of light begins to weaken,” she said.

Amplifiers help boost the light back to its original intensity.

When the laying vessel reaches its final destination it isn’t able to come close to shore.

Buoys are used to float the cable at the surface and it is guided into position by divers, jet skis, and smaller boats.

Finally, the cable is pulled up onto the beach to a ready-made trench, where it’s connected to a beach manhole, a buried container where the undersea cable is hooked up to a terrestrial cable – which in turn connects to a cable station.

These cables are able to channel a huge amount of data around every second.

Stowell said Google’s Grace Hopper cable — which was landed in the UK earlier this week — is set to funnel 340 terabytes of data per second, which would mean 17.5 million people could stream 4K videos at the same time.