Billion-dollar ships heavy ongoing maintenance and care to perform their jobs effectively.
The accumulation of small sea creatures, plants and algae (known as epibiosis) can cause problems for the ships' structure, paintwork and overall performance.
So, it begs the question, how do the undersides of a ship get cleaned?
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Most of the time, they pull them up onto dry docks and carry out a full service. But this is very expensive. We're talking around $1.2 to $1.6 million per dry dock session.
To save money for shipping companies, it's cheaper and easier to clean the underpart while the ship remains in the water.
That's the interesting job of deep-sea divers. Not with the intention of studying cool fish and marine animals but to clean some of the most expensive ships in the world. A YouTube video by Fluctus shows just how scary the job can be.
'Divers are sent underwater to clean the gigantic superstructure and rid them [ships] of these parasites,' Fluctus explained.
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This form of 'ship husbandry' is a tough job involving 'long hours in dark and oily water beneath docks and harbours.'
Divers work alone in 'hazardous conditions under the hulls of gigantic ships.'
The job gets even more dangerous when the diver is directly beneath the ship, as a sudden tide change could cause the ship to slump and trap the diver.
But, there's more to it.
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Deeper cleaning requires a whole different type of skills and expertise.
The world of a saturation diver is a unique and scary one.
For 28 days, divers work in a chamber 15 to 20 feet long that's pressurised to match the surrounding water depths.
'The chamber is equipped with two bunks on the tops, two bunks below and a small pathway in between,' Fluctus described. 'The divers can live in these chambers for up to 28 days breathing in a mixture of helium and oxygen the entire time.'
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Fluctus said: 'Saturation diving is like a mission trip undersea.'
It's carried out by teams of two to three people cleaning in shifts for 'up to six hours at a time' swapping in and out with other divers.
To avoid any fatalities or serious incidents, the entire process is controlled using robots.
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'The use of remotely operated vehicles or ROVs eliminated the problems of human inability to survive underwater,' Fluctus added.
The ROVs are fitted with different tools and controlled from 'the safety of a vessel or ship deck.'
People are amazed at the complexity of the job and the bravery of those willing to work at such depths.
'These divers are incredibly skilled and are heroes to be willing to do such precarious work,' one user commented.
'Saturation diver must be the closest job to astronaut,' another user compared.
Whilst another pointed out that the job is 'Dangerous but satisfying work'.