I have often been fastenated about economic history and its impact on social history. It is my understanding that logs and lumbering in Northern Europe may offer one further logical explaination for not only the Henry Sinclair voyage, but also the importance of the Sinclair family in Northern Scotland. One has to appreciate the demand for logs and lumber from heating to building prior to 1700 for heat, building and perhaps most uniquely for transportation and ship building.
It was this demand for sizeable logs in ship building that became critical. By 1200 the massive long trees used for the keels and ribs of vessels were no longer plentiful. This was obvious all through Northern Europe including Norway. One has to keep in mind that wood vessels have a lifespan in the water and to make anything of the length and size of what was required was not easy unless the major beams were carved from one piece of wood. Joindering was not done with rivets obviously. Now recalling that it takes centuries to grow a tree of this length and dimention and the demand for this critical lumber in construction of everything of any size, then one then has to appreciate that searching for such large trees such as oaks became a critical activity for all the Northern European nations. Now the location of the trees of this size also was an issue. If they existed in the interior access and moving them was deterrent to harvesting them for ship building on the coast.
Now if one looks at a map of northern Europe and looks for the area for old growth forest in say 1200-1500 one has to do a lot of looking. Certainly in the North where trees were a but smaller by natural geography. One looks at Northern Scotland, Norway, Sweden the coast of Finland, Denmark, and then all the way across to Greenland then Labrador and Newfoundland trees of the length required for Viking keels were simply not plentiful. Go south to the Maritimes and to New England and surprise one had such resources again in abundance. In fact the lumber of the New World kept the Navy's of Europe going until 1850 and built the largest fleets for America with the properties of long masts and spars and keels and ribs. Henry's voyage to the new world may have been motivated by a number of mythical and otherwise logical quests, but as Admiral of Scotland, and as an Earl of Norway one of the chief occupations of concern was simply where to find the natural resources to keep rebuilding the ships in use. Again this is one of the simple and obvious explainations for adventure of any sort and while not as glamorous as other explainations, it is simple economic and geographical history. Niven might add this to his list of explainations for the voyage but I presume he has done so.