When Sophie Hardcastle survived sexual violence at the hands of a friend at the age of 23, the first person she told asked her: “Why didn’t you just scream?”

“For a while, I felt quite destroyed by it,” says the Australian artist, novelist and former competitive surfer. Three years later, the traumatic experience forms the central premise of Hardcastle’s new novel Below Deck. It is a story built on the screams of women.

The book is narrated by Olivia, a smart but lonely university grad in her early 20s, who finds herself entranced by the sea when she goes on a sailing trip with two older friends, the wise and always kind Maggie and Mac. Four years down the track – and, spoilers ahead, halfway through the book – Oli is paid to help deliver a yacht from Nouméa to Auckland, and is the only woman in an all-male crew. Below deck, she is raped – and when she tells a fellow worker, he doesn’t believe her. “If you didn’t want it, why didn’t you just scream?” he asks.

“Women have always been considered bad luck at sea,” says Hardcastle, 26, who is now based in the UK, where she was a Provost’s scholar at the University of Oxford. “When stuff goes wrong on a boat it goes really wrong really quickly.” Indeed, a central tenent of Below Deck is the advice given by a friend of Hardcastle’s mother. “You have to know who you are going to sea with and trust them with your life,” she had said, “because no one can hear you scream.”

That rings true for Oli. Not only is she raped, but when she is physically injured in an accident the crew refuse to turn back. And later, when she gets her period early, bleeding over the shared bunk, the men turf her out in a dinghy and drag her behind the boat like a rabid dog.

Raised on the northern beaches of Sydney, Hardcastle published her first book in 2015: Running Like China, a memoir of living with bipolar disorder. Her second, the young adult novel Breathing Under Water, set in a fictional sleepy Australian surf town, came out a year later.

Much of Below Deck was written during Hardcastle’s time at Oxford studying English literature, and it is steeped in literary references as a result. Most symbolic is her nod towards the myth of Medusa, who is raped in the goddess Athena’s temple by Poseidon, the god of the seas. To punish her for violating her sacrosanct space, Athena transforms Medusa into a monster with snake-infested hair.

“It’s one of the very early stories of slut-shaming or victim-blaming,” says Hardcastle. The scene of Oli being banished to the dingy is in a chapter titled Medusa, in a section titled Sea Monsters. The boat Oli is raped on is called Poseidon.

Consent, too, is a key theme. At the age of 16, Hardcastle “had an experience where I was unconscious and woke up to something. That was very clear-cut to me; it was very easy to say that was wrong.” At the age of 23, however, Hardcastle voluntarily visited her friend’s room and “participated in some of it, but also said no to some of it … I wondered if that disqualified any claim for it to be sexual violence?”

As she writes in an essay for the Griffith Review: “I pushed him off me. I pulled up my pants again. And again. And again. I wrote a message so clear, and still I felt him ignore it, turn the page. So then, how do I answer this question: why didn’t you just scream?”

Oli, too, pushes her rapist off her and pulls up her trousers over and again. Yet, when it becomes clear what is happening, she begins to moan – as if mimicking the sounds of pleasure will make it better somehow, or at least make her feel she is in control. It doesn’t. Oli, who like Hardcastle has synesthesia, experiences the world through colour. “The sound of no,” Hardcastle writes, “is sick yellow”.

For Hardcastle there should be no shades of grey when it comes to rape. It is black and white, right or wrong. She insists now: “This idea of a grey area exonerates perpetrators of sexual violence because it allows them to slip into this watery place where the boundaries aren’t clear.”

There is some catharsis for Oli towards the end of the book, when she tells a group of supportive women what happened, naming it as rape. She also, finally, screams: “I scream the way tectonic plates tear apart on the ocean floor, silt and sand and cracked rock … I roar.”

That scream for Oli matters. Hardcastle believes that even if women “don’t scream in the way that the damsel in distress screams in movies, we do scream deep down. I like this idea that sound travels in waves and is rippling out through the sea and eventually all these stories will hit the surface.”

Hardcastle remains wary about naming her former friend, lest it “destroy their lives,” she says. “It is interesting how I could write this book but still be so scared and thinking about how to protect this person.”

In a way, then, Below Deck is Hardcastle’s own scream. “Any sort of sexual abuse takes you out of yourself and you no longer have control of your body and have agency,” she says. “I weirdly feel I got my story back through writing fiction. That is enough for me.”

• Below Deck is out now through Allen & Unwin