The American beat generation author Jack Kerouac is said to have spent just eight days on active service in the US merchant marines on board the SS Dorchester in 1942; but his short stay furnished him with notes for his first novel and, after nearly 70 years, it has now been published for the first time.

The 158-page The Sea is my Brother, a tale of two young men serving on a voyage from Boston to Greenland, has been known about for some time, but is being described by Penguin, its publisher, as "a unique insight into the young Kerouac and the formation of his genius".

The author himself apparently noted: "It's a crock [of shit] as literature."

Literary critics appeared inclined to agree with the author that the text, although showing signs of Kerouac's future style, is raw and juvenile, as well it might be, given that he was 20 when he wrote it.

The literary critic Stuart Evers said: "It is not a great work of literature. It would never be published today if it wasn't by Kerouac, but it is fascinating as an insight into him as a writer … He was just jotting down ideas that he would explore with much more gusto in his later work. There is no real narrative, not much happens, but there are flashes of his later work."

Dawn Ward, the book's editor, said the novel shows a side of Kerouac not normally seen in his books. The manuscript was discovered in Kerouac's archive by his brother-in-law.

Ward said: "It was referred to briefly in letters, but nothing that led anyone to believe that there was this really large volume ... This book is really quite important as it shows how Jack developed his writing process."

The novel joins a growing canon of Kerouac's published works, though it seems unlikely that he ever bothered to lug the manuscript round to publishers, as he did in the 1950s while trying to sell the work for which he is best remembered, On the Road.

Even that book, famously written on a continuous scroll of paper, which brought him celebrity when it was finally published in 1957, was issued in an unexpurgated edition only four years ago and another early work, And The Hippos Were Boiled in Their Tanks, written with William S Burroughs in 1945, only saw the light of day in 2008.

Kerouac described The Sea is My Brother as being about "a man's simple revolt from society as it is, with the inequalities, frustration and self-inflicted agonies", which certainly makes it sound like an archetypal adolescent novel. He noted down such prototype characters as "the vanishing American, the big free by [sic], the American indian, the last of the pioneers, the last of the hoboes".

The book's chief protagonist, Wesley Martin, is, like the author, a college dropout, who he wrote, "loved the sea with a strange, lonely love, the sea is his brother and sentences. He goes down." By contrast, another character, Everhart, "escapes society for the sea but finds the sea a place of terrible loneliness".

The two spend the book arguing, drinking and contemplating isolation, which looks pretty much as though they mirror Kerouac's own life.

After many years mingling with and befriending other writers of the beat generation, such as Burroughs, Allen Ginsberg and Gary Snyder, and much time unsuccessfully trying to interest publishers in his work, he found himself disoriented by the fame On the Road brought him.

He became unbalanced by critics such as Truman Capote, who said of his much-honed, stream of consciousness writing style: "That's not writing, it's typing." Kerouac drank himself to death at the age of 47 in 1969, leaving behind a small oeuvre of semi-autobiographical novels and a host of devotees.

Paul Giles, professor of English at Sydney University, told the Australian network the ABC: "The Sea is My Brother will fit with the sort of American literary tradition of sea narratives, going back to Moby Dick and Richard Henry Dana and others. I think it's definitely worthwhile [but] I suspect the sales will be more to academics rather than popular audiences.

"I think Kerouac has taken on a kind of eminence gris aspect rather like Ginsberg and JD Salinger, and people who were once thought of as rebellious and counter-cultural and are now seen as very much part of the institutional formation of American culture after the second world war."

Review

The publication of On the Road in 1957 made Jack Kerouac an instant literary icon – an ironic fate for a writer so desperate to be seen as iconoclastic. He was even more desperate to be seen as a literary genius, but Truman Capote spoke for many when he said On the Road was not writing, just typing.

Now comes Kerouac's first novel, The Sea is My Brother, written when he was 20. That it never found a publisher during his lifetime is not hard to understand. When he was older and wiser Kerouac called this effort "a crock". But that hasn't stopped Penguin from padding it out and touting it as "a unique insight into the young Kerouac and the formation of his genius".

Sadly it would take another 15 years and colossal amounts of Benzedrine for the genius to emerge; there's certainly none here. The writing should be entered in a bad prose competition. For instance, people in this book never speak: they offer, reassure, ask, explain, shrill, inform, continue, confess, urge, sing, greet, smile and yawn.

It tells the aimless story of two young men who get drunk and join the merchant marine. One of them has been teaching literature; he provides Kerouac's excuse for adolescent philosophising, embryonic rhapsodies to America and strained efforts at literary exaltation – what Kerouac would later call "beatification" (the source of the nickname he gave his Generation) – as well as literary allusions for borrowed gravitas, helpfully explained by an editor who seems even more callow than the writer.

The reader who survives this is rewarded with unfinished juvenilia, including a journal that wonders, as countless unreadable journals have before and since, whether some eminent bearded "professor may even look upon my puerile efforts" as remarkable and valuable treasures of American contemporary youth. Puerile, yes. Treasures, no.

Sarah Churchwell