There are the ever-surfacing tales of the ghostly outline of a sunken caravel seen off Ripiro Beach from a small aircraft after a massive tidal sand shift, then lost again; reports, too, of shipwreck timbers found along the beach that point to pre-Dutch or English vessels.
At times, Cowie found himself navigating choppy waters stirred up by "outlandish" theories presented by others in the past, and a perceived disrespect of cultural issues and lore.
He spent years putting together the pieces and probabilities, the oral histories of local Maori and Pakeha, the ancient maps. What and where is the evidence, he asks? Now a marine policy management adviser to the Abu Dhabi Government, here Cowie talks about Conquistador Puzzle Trail, launched at Dargaville in July.
"ONE EVENING in 2006, my father Mike and I were watching the New Zealand Maori rugby team play on television.
I asked him why a tall, fair-skinned and ginger-haired fellow was playing at lock.
Dad, a history and geography teacher, said that he thought it was related to some shipwrecks on New Zealand's rugged northwest coast that might be of Spanish or Portuguese origin.
And so began my Conquistador Trail.
I drove up north soon after to Dargaville, where I was born, and met a number of knowledgeable people at the local museum. What they had to tell me only deepened the mystery.
Sixteenth-century maps of New Zealand and Australia; shipwrecks; oral folklore of white voyagers coming ashore wearing armour; their massacre by natives; cannon, helmets, a ship's bell, ruins, stone crosses and other enigmatic artefacts found in the vicinity centuries later; red-haired and fair skinned Maori noted by the next wave of voyagers to New Zealand; buried treasure; pohutukawa trees on the far side of the world; lost caravels ...
Did the Portuguese and Spanish conquistadors discover New Zealand and Australia?
In my view, yes - the Portuguese most likely, on the balance of probabilities, discovered Australia and New Zealand between 1520 and 1524.
For the first time, what I like to call "conquistador puzzle pieces" are all presented in a book in a balanced way, with the key arguments for and against each puzzle piece's antiquity. Readers can make their own informed view on whether history needs to be revised.
In the past, authors writing on this subject have claimed the same puzzle pieces to fit with their theory, whether to argue Portuguese, Spanish or Chinese discovered New Zealand.
I haven't done that. Conquistador Puzzle Trail brings an objective approach and aims to cut through the swathes of smoke billowing around the subject. Each puzzle piece is presented on its own merit. If a piece doesn't fit, it doesn't fit; I have not tried to twist it to fit with the theory.
So what is the evidence? Let me start with a group of 16th-century maps called the Dieppe maps. Dieppe, in France, was where cartographers and mapmakers congregated in the 1540s, 1550s and 1560s.
There are two peculiarities of the Dieppe charts. The first is that in the place of modern-day Australia, there is a landmass called Big Java. The other is that there are a number of Portuguese placenames on Big Java, with over 120 Portuguese names on the most detailed map, the Vallard atlas of 1547.
The maps are the starting point for Iberian discovery theory, and for over 228 years researchers have put forward theories in respect of their origins. The detail on them is breathtaking.
In 1803, William Faden, Royal Geographer to King George III and also the Chart Committee of the British Admiralty, reassessed what was known of the world. On the chart of the Indian Ocean he wrote next to New Zealand: 'New Zeeland (Discovered and named by Tasman 1642 but where eastern coast was known to the Portuguese, about the year 1550).'
Similarly, in 1894, two New Zealand historians, Dr Thomas Hocken and Dr Robert McNab, theorised that further research might reveal the true story of the discovery of New Zealand: 'Doubtless before Tasman, there were voyagers who had visited New Zealand. We are justified in thinking that there are buried in the old archives of Portugal and of Spain journals [that would prove this].'
In the 20th and 21st centuries, the likes of Australian Kenneth McIntyre and, more recently, Peter Trickett have had similar views.
Simple human deduction has not changed in 228 years. A person looked at a map over two centuries ago and, seeing the similarities in the coastline to a continent, coupled with the Portuguese names, drew a conclusion on it; voila. We can do the same today.
To go a layer deeper, back in the 1970s at Fraser Island off Australia's Queensland, three scientists were investigating the geological history of sand and pumice layers. At that point on the Vallard map, dated 1547, the word pomezita appears, a Portuguese reference to pumice.
With a hand-held auger, one of the scientists struck what turned out to be a sand-encrusted lead sinker at a depth of 2.2 metres. What on earth was a lead sinker doing 2.2m into a pumice layer probably formed around 1410-1630AD? The next word on the Vallard map offers a clue - camonron, which means prawns.
Coincidence? Yeah, right. Pumice and prawns were there in the 16th century and are there today.
The sinker? Trickett hypothesised it was from a 500-year-old prawn net used by a Portuguese ship mapping that coast.
Here's the question: Would a 16th-century cartographer make up the coastlines and creatively name more than 120 places? And if they did, isn't it too much of a coincidence they guessed what the coastline may look like and knew that pumice and prawns were there?
And for what it's worth, the midpoint between the lead sinker date range of 1410-1630 is the time of the most probable discovery of the Antipodes, the voyage of Portuguese nobleman Christovão de Mendonça in 1520-24.
Have a read of Conquistador Puzzle Trail, assess each puzzle piece on its own merit and form your own view. I think you'll be as surprised as I was. And I haven't yet mentioned the Spanish ... "