For the majority of landlubbers, the fact that the world’s oceans are clogging up with the detritus of a rampant consumer society can easily be ignored. For most, the watery expanses beyond our coastlines might just as well be another planet.

Not so for the crews of the fleet of high-speed ocean racing yachts currently competing in the Volvo Ocean Race around the world, which spend up to three weeks at a time at sea racing day and night. For them the effects of ocean littering are all too obvious.

British double Olympic silver medallist Ian Walker skippers the Abu Dhabi Ocean Racing team and is competing in his third race around the world. In more than 100,000 miles of ocean racing, Walker says he hasn’t hit anything major – yet. It may be just a matter of time – on a high-speed training run across the Atlantic this summer Walker and his crew narrowly missed hitting a household fridge-freezer bobbing in the middle of the ocean.

“We passed within a boatlength of it,” Walker remembers. “Fortunately we saw it. It could easily have put a hole in our boat.”

As incongruous as having to dodge a fridge-freezer mid-ocean might seem, Walker says that encounters with manmade waste afloat on the ocean happen all too often.

“The most common things we see are plastic bottles and fishing debris like buoys and rope, but I remember sailing near the Philippines in the South China Sea and we had to weave our way through a whole lot of cut logs – just like someone had emptied a trailer-load in the sea.”

Like all good mariners, the sailors keep a watch for objects floating in their path during the day. “Wherever we are, we see plenty of plastic bottles bobbing by – with and without tops,” says New Zealander Daryl Wislang. “Generally they are completely encrusted with barnacles, which gives you some idea of how long they have already been around.”

Once darkness falls, all the sailors can do is hope they don’t run into anything as they charge along at more than 30 knots (35mph). At those speeds a collision with a log or a fridge-freezer would almost certainly cause catastrophic damage to the hull, keel and rudders – at best putting the crew out of the race and at worst endangering their lives.

“It’s my biggest fear,” Walker confesses. “There’s nothing you can do except keep your eyes open during the day and keep the watertight doors closed in the bow at night in case the worst happens.”

The two most debris-ridden sea areas Walker has raced through are the coastline of Vietnam and the Malacca Straits between Indonesia and Malaysia. “In addition to fishing nets and domestic waste, you have to deal with plenty of natural debris, too – floating islands of trees and reeds are a common sight.”

Despite stories of seafarers encountering remote mid-ocean “islands of trash”, Walker says he has never seen anything like that and describes the open oceans he has sailed as “very, very clean. But things deteriorate dramatically as you approach land,” he adds. “It is only by sailing in the clean ocean that you realise how dirty the water is near land.”

Walker says the most dramatic example of coastal pollution he has witnessed was during the 2008-09 Volvo Ocean Race on the leg from Qingdao, China, to Rio de Janeiro in Brazil (the controversial choice as the venue for the Rio 2016 Olympic sailing regatta). “We were about 50 miles out when the water suddenly changed colour from blue to brown. Straightaway you could smell the pollution. I would never swim in the sea there.”

Although some ocean debris falls or gets thrown from cargo ships or is left behind by fishing vessels, by far the greatest proportion originates on land and finds its way out to sea by a deliberate act. “It is never good to see the negative effect that we humans have on our planet. I am always shocked when I walk on the beach at home in the UK at how much rubbish there is, particularly after a big storm,” he says. “In all cases I think the polluter must be forced to pay, whether it is sewage, shipping containers or other rubbish. Authorities need to stop treating the oceans as a rubbish dump and start treasuring them for what they are – one of mankind’s finest natural assets.”

Justin Chisholm is communications officer for Abu Dhabi Ocean Racing. Follow the race at volvooceanrace.com