AS she looks up at the great iron hull of the ss Great Britain, children's writer Sue Purkiss would be forgiven for catching the figure of a young girl in a red coat slip past, out of the corner of her eye.

It's not that Sue has slipped into a scene from the classic 1970s movie Don't Look Now, more that she's spent a lot of time onboard this ship in her own imagination over the past few months – and Emily, the girl in the red coat, has been beside her every step of the way.

Sue's latest book – Emily's Surprising Voyage – tells the story of a young girl emigrating to Australia in the 19th century onboard Brunel's iconic ship.

"I've been around the ship half-a-dozen times over the past 30 years," explains the Cheddar-based writer. "I remember coming here in the early 1980s with my father, who was a steam engineer and so was fascinated by the ss Great Britain.

"Back then, the interior of the ship hadn't been refitted, and I struggled to get my head around where everything would be – but he was able to paint a picture in my mind of how it would have looked, because he understood exactly where the different parts of the engine would go."

But it was almost three decades later, when Sue visited the fully-refitted ship, that she had the idea of including it in a story.

"I came here with visitors, who were staying with us for a few days and had never seen the ship," Sue recalls.

"As I was walking around I read an information board about a man called Captain John Gray, who had been the captain on the Great Britain during much of her time as an emigrant ship in the 1800s – taking emigrants out on the long voyage to Australia.

"According to all contemporary accounts, it sounds like he was a wonderful character, and was very well liked. He used to go down into steerage at regular intervals throughout the day, to check the poorer passengers were all keeping healthy, and he would always encourage them to get up on to the deck to take the air and have a bit of exercise.

"His story ended tragically however. It is believed he committed suicide by jumping out of the porthole in his cabin during one of the long voyages away from home.

"While his ending didn't seem like the stuff of a children's tale, I was drawn to this figure of a kindly captain who cared for everybody onboard."

The former English teacher began her writing career 15 years ago, after taking a course in creative writing at the University of Bristol.

"I left my full-time job as a teacher at Cheddar after my daughter had a stroke at the age of seven, and needed round-the-clock care. Thankfully, she has now made a full recovery, and is training to be a teacher herself these days.

"Once it became clear that she was on the mend, I decided to sign up to the writing course – just as a hobby at first. One small part of the course was about writing for children, and for some reason, I really got into it.

"I started writing stories about ghosts and witches, and really enjoyed the freedom of it.

"Then, I eventually managed to get one of my stories published. It was called The Willow Man, and was inspired by the figure next to the M5 at Glastonbury.

"That led to a second book, an historical drama about King Alfred the Great's life in Somerset.

"I enjoyed the challenge of writing accurate but entertaining historical fiction that young people could engage with, so I wanted to do another historical piece for my next book – that's when the idea I'd had about Captain Gray came back into my mind.

"The distinctions between the first class passengers on the ss Great Britain and the steerage passengers fascinated me, so I decided to make my central characters a young girl travelling in first class, and a young boy travelling in steerage.

"My publisher, Walker Books, liked the idea and were able to find a wonderful artist, James de la Rue, to come up with the illustrations.

"I think he's done an incredible job. All too often, children's book illustrations are more like cartoons, but James' pictures are complex and wonderfully evocative – he's managed to capture the story in his drawings in exactly the way in which I'd imagined it as I was writing.

"If anything, it's brought my characters even more to life for me."

● Emily's Surprising Voyage, by Sue Purkiss, is published by Walker Books, priced £3.99.

● The Evening Post is supporting the ss Great Britain Trust's project to build an impressive new £6 million archive, the Brunel Academy. Since launching our campaign earlier this month, the people of Bristol have donated £24,058 towards the £35,000 shortfall. To make a donation, complete the form on this page and return it to the address given.