Climate change campaigner Greta Thunberg will set sail today from Plymouth to attend the UN Climate Action Summit in New York.
The 16-year-old is making the journey to America without using a plane and, alongside her father, will join two crew members on a racing yacht.
The journey will take around two weeks.
Greta has spent the last two days training on board.
"I am not at all worried about my safety because I know this is a very safe boat and the crew and sailors are very experienced," Greta said.
"I feel a bit sea sick and it's not going to be comfortable but that I can live with."
The Malizia II yacht will allow Greta to make a zero-carbon Atlantic crossing. It has two hydro generators which are lowered into the water to generate electricity as well as solar panels on deck.
But for all the technology, there will be no home comforts on board.
There is no shower, no heating and no toilet.
:: Listen to the Daily podcast on Apple Podcasts , Google Podcasts , Spotify , Spreaker
"We will have to do it in a bucket - but that's fine," Greta said, adding that the group would pour boiled water into freeze-fried food bags for their meals.
"That is quite good - I don't need fancy food," she said.
The yacht will be skippered by Boris Herrmann from Germany - who has sailed three times round the world, once non-stop.
He will take a southern route through the Atlantic and try to avoid storms but he admitted Greta and her father will experience highs and lows.
He told Sky News: "The life on the boat depend on the wind and the sea conditions so I hope very much for them and for me that we have some beautiful moments of sailing but very sure we will also have some tough moments - they know about that and think they are pretty well prepared already mentally for this challenge."
"I have split feelings - at the same time excited in a positive way, at the same time a little bit anxious," he said.
"This is unheard of, this has never been done, completely inexperienced people sailing on a race yacht across the Atlantic - it has never happened before so we don't know how it's going to be."
Greta Thunberg started the #FridaysforFuture movement which has inspired children around the world to go on strike from school on Friday to raise awareness of climate change.
The journey to America is another chance for her to push her message: "Why not act as soon as possible?
"Because if we act now we still have everything in our own hands.
"If we wait much more then we could pass several tipping points that we can't go back from."
Greta will attend climate change demonstrations before joining the UN Climate Action Summit on the 23 September.
She will then make her way to Chile for the COP25 Summit in Santiago in December.
During the summit she will tell politicians: "Teenagers and children - it is not our responsibility.
"What we are doing now is we demand you take your responsibility and do something. Our job is to demand solutions not provide solutions. We are demanding a solution not providing them."