In Chapter 16, the peach continues to gather speed and momentum. It rushes straight past the people walking up the hill to see it, and everyone begins diving left or right in order to avoid getting squashed. It rolls across fields, roads, and towns, taking down anything that is in its way. At one point it breaks through a chocolate factory, leaving two holes in the building, and chocolate flows out of the factory and into the streets. Children began swimming in the chocolate and try to eat it, but the peach just keeps rolling.
Suddenly the peach approaches the sea where James used to live, the sea that he wanted to visit the other day; there is a line of steep, famous cliffs facing the shore. The sea is described as very dangerous, and it appears that there is no hope for James and his new friends as they plummet off a cliff and into the water. The peach is submerged but then floats back to the top, sitting easily on the surface of the sea.
James, Centipede, Earthworm, Miss Spider, Ladybug, Glow-worm, and Old Green Grasshopper are recovering from the rough-and-tumble trip from the garden to the sea as Chapter 17 opens. They had been flung back and forth, and now they are tangled up with one another. They begin to sort everything out with the help of the Glow-worm's light, then start to speculate about where they could have landed. They eventually decide to go to the top of the peach and look around, a much safer alternative than going out the side entrance, since they don't know where they are. Miss Spider busies herself with weaving a ladder from the floor of the peach to the roof, and the others assist Centipede as he puts on his 42 shoes. When the shoes are on and the ladder is finished, they all climb to the roof, excited about what they might see next.
In Chapter 18, everyone is shocked to find that they are in the middle of the sea. The Earthworm proclaims that they are all finished, destined to drown, at least until James explains the peach is actually floating. Although the Old-Green-Grasshopper maintains that everything will be fine in the end, Earthworm tries to upset the others by insisting they are still in a bad situation - they have no food. James interrupts again by explaining that the entire ship is food - they can gradually eat the peach, and they will have no problem surviving for weeks and weeks without destroying the peach as a vessel. Earthworm, very flustered, now says that the problem is that there is no problem! The others joke with him that he is always looking for something to complain about.
James and the creatures all begin to eat the peach, and find that it is simply delicious. Many of them say that it is the most delicious thing they've ever tasted, and Centipede bursts into song. He details all of the delicious things that he has eaten in the course of his life, concluding that this peach is the best of them all. Everyone is joyous and content.
Everyone has just finished their meal when, at the start of Chapter 19, Centipede spots "black things" gliding through the water. Earthworm identifies these black shapes as sharks, and while the others silently agree, they are too afraid to admit it themselves. The characters try to create a false sense of security by saying they are safe if they stay atop the peach, but suddenly the sharks begin to attack the peach by eating chunks of it. Desperate, the creatures call out to James and beg him to think of a way out of the disaster.
In Chapter 20, James announces that he might have an idea of how to escape the sharks, but he is not sure if it will work - he needs string. Assuming that there is no strong onboard, he believes his plan destined to fail, but the creatures reveal that Silkworm is actually below; James just hasn't seen her yet. Both Silkworm and Miss Spider are capable of spinning as much string as James needs. He tells them more about the plan, and reveals that he is going to lure seagulls towards the peach with Earthworm, then loop strings around the seagulls' necks and tie the strings to the stem of the peach. If he can do this with hundreds of seagulls, James believes that the birds will lift the peach up into the air with the power of their wings.
The others believe that the plan is crazy, and Earthworm is appalled that he is going to be offered as bait. It takes some effort for James to get his point across, but finally at the end of the chapter he quiets his friends' doubts and explains that the Earthworm doesn't need to die (since he can easily be pulled out of danger) in order for the plan to be successful.
The power of the peach is overwhelming in this section. This gargantuan fruit tears through anything that stands in its way, flattening cars, knocking down telegraph poles, and breaking through buildings. James needed a powerful push to break away from his aunts and reclaim his happiness, and the peach carries him to freedom in the most dramatic manner possible. Dahl creates anticipation as the peach keeps moving and approaches the sea, particularly when he describes how dangerous the sea is. Dahl also takes a moment to allude to one of his other works, Charlie and the Chocolate Factory, as the peach breaks through the famous chocolate factory in a nearby town.
These chapters showcase Dahl's favorite techniques and topics in other ways. When Centipede bursts out into song, he utilizes a rhyme scheme that is found in other parts of the book as well. Every other line in the verse rhymes, with a new rhyme starting at the beginning of each verse. Centipede had sung a similarly-rhymed song before the peach was released from the tree. These songs are meant not only to advance the story but also to reveal more information about the Centipede and the other characters. Both songs come at the end of their chapters, with only one short paragraph following them before the chapter concludes.
Over the course of these five chapters, James begins to develop into something of a hero. He skillfully thought of solutions to tense situations: he reassures the creatures that the peach will not sink and alerts them to the food source at their disposal. When the sharks begin to attack, his new friends turn to him once again, dependent on his skills to save them. The faith and trust that his new friends have placed in him is refreshing and renewing for James, especially because of the constant verbal abuse and generally demeaning treatment that his aunts inflicted upon him; now, he is no longer seen as stupid and worthless, but as worthy of respect and attention.
The nurturing nature of the female characters fosters new self-confidence in James. Miss Spider and Ladybug especially are kind and encouraging. While most of the characters are insisting James's plan is ridiculous and impossible, Ladybug encourages him to continue describing his plan. Without her support, James may never have gathered the confidence necessary to propose his plan to save the peach and everyone on it from the sharks.
Throughout all of these chapters, the story reaches short climaxes where it appears that the peach and everyone on it are doomed: the giant fruit catapults over a cliff, lands in the sea, and is surrounded by sharks. In each of these instances, the Earthworm exudes negativity and argues that there is no hope. Dahl builds tension quickly in each of these instances, but every time this tension is quickly resolved, indicating that a larger climax is yet to come.