Countryistan is a large island nation approximately 3,000 kilometers from the nearest landmass.
The government of Countryistan is secretly planning on committing genocide and ethnic cleansing against a portion of its population in about a decade.
A powerful billionaire/member of the ruling party who's secretly sympathetic to said portion of the population, and who knows what's going to happen, happens to own an oil company which owns an ultra-large crude carrier - a huge ship designed to transport enormous quantities of unrefined crude oil.
Said ULCC is currently in a high-quality shipyard specially-built to accommodate it. It is intended to leave within a year or two on a shakedown cruise to a nearby country; however, the billionaire and the higher echelons of their company are constantly sabotaging it in order to cause enough of a delay for it to be retrofitted.
Said billionaire wants to turn said ULCC into a transport, fill it with the people most likely to be murdered by the government, and then send it on its 3,000-kilometer cruise. Once it and its passengers arrive in a safer place, it simply won't come back - or, maybe it will, minus its passengers, and it'll just keep going back and forth until the plot gets found out.
This billionaire and their company have the resources to keep government inspectors away from the ship - they own a good portion of the country's shipbuilding industry, but have little power otherwise due to deliberate factionalism within the ruling party. They can do many things covertly, however; money talks.
For the purposes of this question, the ship is the Seawise Giant. It has the following characteristics:
- Full load displacement: 657,019 metric tons (646,642 long tons)
- Capacity: 4.1 million barrels of oil (574,000 metric tons of oil, or somewhere between 604,211 and 820,000 cubic meters of oil)
- Length: 458.45 m (1,504.10 ft)
- Beam: 68.6 m (225.07 ft)
- Draft: 24.611 m (80.74 ft)
- Depth: 29.8 m (97.77 ft)
- Speed: 16.5 knots (30.6 km/h; 19.0 mph)
Additionally, it is nuclear-powered, with a reactor/turbine combination that puts out as much horsepower as the real-life Seawise Giant's engines. In-universe, this is seen as perfectly normal and not suspicious. It does not require refueling within the timespan of this question.
How do we modify this ship to carry the maximum number of people possible, taking into account the following conditions?
The ship has to look the same on the outside as it would if it were unmodified - both above and below the waterline. There can be no extra structures on the deck, no holes in the hull, and nothing, visually speaking, that gives away the fact that the ship is full of refugees, or, for that matter, invites any form of suspicion.
The ship has to displace roughly the same amount as it would if it were empty and unaltered, because, if it rides too low or too high in the water, it'd be suspicious-looking. A small margin of error is acceptable here.
The ship has to move as quickly as it would if it were empty and unaltered, since if it was moving slowly, it'd draw suspicion (and also require more supplies for the refugees). This means 16.5 knots, bar a small amount that could be explained away as engine trouble.
Anything that does not change the outside appearance of the ship, its displacement, or its speed is fair game. For instance, the guts of the ship can be pulled out and replaced with their weight in people and supplies for said people, and blocks of concrete or steel can be put on board in order to add enough weight to make it settle in the water correctly.
People should not die en-route, other than by accident or things they were already going to die of. If someone dies of cancer, that's fine. If someone dies of dehydration, it's not. It will take 98-ish hours for this thing to get from Point A to Point B, and probably another 12 on either end for loading and unloading. No simply packing people in like sardines; there has to be enough room to sit down, enough below-the-deck restrooms for people to use the bathroom, adequate ventilation, food for about 5 days, etc. It does not need to be comfortable, though; it just needs people to not die/go insane long enough for it to arrive on-target.
Your budget for modifications is equivalent to $20 billion in present-day dollars.. The ship itself, the nuclear reactor, shipyard, provisions, operating costs, and the like are all accounted for; this budget is only for modifications. The shipyard facilities are top-of-the-line.
To reiterate, the nuclear reactor and the subsequent lack of exhaust are seen as perfectly normal, and not suspicious.
The ship is already fully built. It will need excessive reconfiguring in order to serve its purpose.
You have 9 years to get these modifications finished. I believe this is reasonable, considering that Seawise Giant was built within 5 years.
Getting these people on board isn't a problem. The billionaire and the company just pretend to be killing the people, they disappear (in reality, via the ship) and the government doesn't figure it out.
Getting these people off the ship isn't a problem either. The billionaire and their company have set this up in advance.
Assume Earth-standard conditions - for instance, approximately 9.8 m/s^2 of gravity, 101.325 kPa air pressure at sea level, human-breathable atmosphere, seas made of water, etc. Additionally, assume a modern-day tech level.
I will add more to/edit these requirements if someone points out a glaring absence in/flaw with them.
And don't you tell me that anything less than 8,000 can fit on it once it's retrofitted; the world's largest cruise ship can fit more than that, it's smaller than this thing, and its design prioritizes comfort over efficiency.