Every age rewrites history to its own liking

I'm reading "The Isles, a History" by Norman Davis. He is something of a fruitcake, and spends a lot of words discussing how the mean old English oppressed the noble "Celtic" races, Welsh, Scots, and Irish, going right back to the beginnings of history. But he has some modern myths to propagate as well as serving as a scourge of the Sassenach.
Davis is discussing the Vikings and their impact on England. Which was considerable, at its high point the "Danelaw" covered half the country. There is the interesting question of why the Viking appeared so suddenly out of nowhere. They first struck the monastery of Lindisfarne in 793. Prior to 793 nobody in England had heard of them. Davis says,
"The central puzzle... is to know why, after an age of passive isolation...The answer obviously has something to do with a serious ecological imbalance....Historians refer to changes in climate..."
How PC of Davis, it's all due to global warming, Viking cook fires added to the CO2 level in the atmosphere. Yeah, Right.
More likely, the Viking shipwrights didn't learn how to build a ship seaworthy enough to cross the North Sea until 793. Heh, there is a first time for everything. There is a lot of art in building a sailing vessel that can reach across the wind and beat up into the wind. You need enough keel to keep the ship from sliding sideways under the press of sail. You need a sail that can be trimmed in to fore and aft, and you need the mast placed just right. Too far forward and the force of the wind pushes the ship's bow down wind overpowering the rudder. The far aft, and the opposite happens. The Vikings built the hull from long planks (strakes) and they overlapped the planks and riveted them together. This sophisticated construction ( we call it monocoque today) gave an immensely strong and light hull, but required a lot of hand made iron rivets and a set of really big clamps to force the planks tightly together so they could be riveted.
We have a few ship finds from before the Viking age, (Sutton Hoo for instance) and it is clear that these vessels were pure rowboats, no keel, no mast or mast step. They might have been good enough to cross the English Channel in nice summer weather, but crossing the North Sea is much harder.
As late as 1066, Duke William's invasion fleet had to wait months for a south wind to carry them to England. Translation, the Duke's hastily built ships (we can see them abuilding in the Bayeux Tapistry) were only fit to run before the wind. Tubs like that would never hack it in a North Sea storm.