The unknowable expanse of the oceans has become a little more familiar after Blue Planet II. Now it is set to become more familiar still to tourists with enough cash to spare.

The BBC series is the most-watched show of 2017, with 14.1 million viewers tuning in for unseen wonders like cannibalistic Humboldt squid, methane belching from the ocean floor and an underwater lake of brine. Scenes like these are beyond the view of anyone except TV crews, scientists and explorers – but not for much longer. Submarine tourism is riding a wave of interest that is likely to swell as the series continues.

Bubble-shaped submarines like the ones used in Blue Planet II are the new must-have accessory for high-end cruise liners around the world. The first large deep-diving tourist submarine will go into service in Vietnam in 2019, and next year a luxury submarine will start running tours to the bottom of the Atlantic to see the Titanic.

One of the companies investing in submarines is Scenic, which is equipping its newest cruise ship, the Eclipse, with two six-seater subs for its launch next year. The 226-berth vessel will begin operations in the Mediterranean, then make its way to the Arctic, according to brand manager Nichola Absalom.

“The fact we can take people to the Arctic and Antarctic means people can see the whales and the polar bears and penguins in their natural environment,” Absalom said. The Eclipse’s submarines will reach depths of about 200m – the edge of the mesopelagic zone, the oceans’ twilight zone where not enough light penetrates the water to support plant life. Other tour operators have their sights set much deeper, on the bathypelagic or midnight zone.

Elizabeth Ellis, the founder of Blue Marble Private, a luxury travel company in London, has been working with the US firm OceanGate Expeditions to build a nine-berth submarine that will sail from Newfoundland to reach the wreck of the Titanic, about 3,800 metres (12,500 ft) below sea level. The tours start next year, with two already sold out and more planned for 2019, although with tickets priced at more than $100,000 it’s not for everyone.

“When you have a submarine that can go to those depths, the possibilities are endless,” Ellis said. “The Titanic is obviously an iconic site, but as Blue Planet showed there are many other places, hydro-thermals for example. We are on the cusp of something extraordinary.”

The number of cruise ships with submarines has been growing steadily over the past two years. The Malaysian company Genting has four ships equipped with submarines made by the Dutch company U-Boat Worx, which has five more in production.

Other cruise ship and superyacht subs are made by Triton, based in Vero Beach, Florida, which also built the submarines used by the BBC. Triton’s co-founder, Patrick Lahey, is one of the pioneers of the new bubble subs. Aston Martin recently announced a tie-up with Triton to produce a $4m submarine for the super-rich as the ultimate super-yacht accessory.

“Ten years ago I was going round yacht shows and people would laugh at me: ‘Here’s the guy who wants to put a submarine on your yacht’. Now the yacht manufacturers are coming to us,” Lahey said. “Shows like Blue Planet are capturing the imagination the same way that Jacques Cousteau captured mine.” Lahey watched the French underwater explorer’s American TV documentaries in the 1970s and was inspired to become a commercial diver.

One of the Triton submersibles used in the filming of Blue Planet II. Photograph: Luis Lamar

He worked for a Canadian company, Atlantis Submarines, which began running submarine tours in the 1980s in the Caribbean, Hawaii and Guam. These vessels could go only slightly deeper than scuba divers – up to about 40m. “There are now a number of vessels that are extremely capable of much deeper diving.” Triton is building a new 24-seater submarine for a Vietnamese company, which will operate in depths of 100m. The smaller leisure subs will go down more than 300m.

Key to the growth of leisure and tourist submarines is acrylic engineering.. “There’s nothing quite as exciting as a transparent pressure boundary,” Lahey said, referring to the clear acrylic domes seen in the Blue Planet II subs which are 30cm thick. “The ability to manufacture them, to make them bigger and better, has really made a difference.”

Submarines are a more convenient way for people to see the ocean depths than scuba diving, Lahey said, because they are pressurised at about one atmosphere. It means passengers can go straight back up the surface and step out of the vessel. Scuba divers typically go no deeper than 30m and must ascend gradually to avoid decompression sickness, known as “the bends”.

The other improvement fuelling the growth of submarines is batteries, according to Eric Hasselman of U-Boat Worx, who pointed out that basic submarine technology had not changed conceptually since a Dutchman called Cornelis Drebbel managed to take a submarine down the Thames in 1620, burning saltpetre to create oxygen.

“What’s changed is battery technology,” Hasselman said. “With the same volume and weight we have 10 times more battery power now. It means our submarines can go 18 hours without recharging.”Is there a risk that growing numbers of submarine tourists might inadvertently spoil the marine environment? Both the Marine Conservation Society and the Blue Marine Foundation believe that submariners should create a code of conduct, rather like surface tour operators who visit the UK’s main sea wildlife spots. “They have to sign up to a code of conduct agreeing that they won’t chase after animals and keep a safe distance so as not to disturb them,” Richard Harrington, of the MCS, said.

Hasselman believes the risk of environmental damage is low: “All submarines apart from military ones are battery-powered, so there’s no pollution. Fish are not scared of submarines and big mammals come close to observe what has come into their territory. Although hopefully one day there will be enough submarines that we need a traffic light system.”