It is such an unnecessary error as the boat builder could not have been unaware of it, so I can only presume it has been done as a result of some unknown directorial decision.
Would this bother a layman? Probably not and that is the point. A series like this is not designed to satisfy experts, it's designed for mass audience entertainment..
As for the rest of it, the production values are generally cinematic while the casting is dramatic as is often the case with such features. This leads to the usual "cast of tens" problems. Keeping the shots close and tight helps to some degree but there's not much else that can be done about that without budget breaking CGI.
The costume has the usual issues. We call it the Jabberwocky Effect. (Everyone in the past wore brown or black and was covered with s****. ) There is no reason to assume that they didn't wear colour just as much as us, it was just likely to be less bright as natural dyes tend to fade faster.
Ultimately costume departments throughout the industry suffer the same problem. Costume designers always want to put their own stamp on a production and only ever use historical sources as "inspiration" Never expect them to get it right because that would simply not be creative enough for them.
Since armour usually falls under the costume departments responsibilities this leads to some of the more outlandish creations that we see in films which are otherwise quite well propped. (13th Viking is a good example which springs to mind.) in this respect, the general scarcity of armour depicted, at least amongst the Vikings, seems quite plausible
The properties department usually works to a different ethos. For them there is more prestige in creating the right look. That doesn't always mean they get it right but it is often closer. Property managers have recently become aware of the traders and craftspeople supplying the re-enactment markets, which is an improvement but they still rely heavily on the cheaper "ethnic" suppliers which leads to a fusion of the good and the bad. Overall, while being far from "accurate" the visual effect and feel of this series is not too bad, although the obvious gas log hearth in the main longhouse does irritate me every time I see it.
Plot wise, there is an interesting blend of the mythic with the historic. The edges between the characters and their beliefs, both heathen and Christian, is distinctly blurred and that seems completely in keeping with the ancient mindset as far as we are ever able to understand it. This ambiguity is also present in much of the Nordic and English saga sources too. It is impossible to address this period of history without some reference to the shifting religious structures of Europe and Scandinavia at the time and I think they have written this quite well for a modern lay audience. Inevitably, historians, archaeologists and other enthusiasts will find plenty of things to find fault with.
A point has been made that some of the mass audience often looks upon such entertainment as being factually correct in some way, which is a fair point. This is exactly the problem that I have with the dangerous antics of Grylls in his pseudo factual "entertainment" programs.
As far as this series is concerned, I think that they have created a format that gets more right than it gets wrong. Although it does indeed concentrate upon the usual dramatic stereotypes for the sake of action, compared to most such offerings, I think it does at least hint at an agricultural back story. (Burning of the grain stores, negotiating for farm land etc.)
