Alright, departing from my usual fantasy setting to something of a thought experiment. Let's say, for argument's sake, some Dane longboat captain in the 10th or 11th century worked out how to make a primitive compass and, while serving in the Varangian Guard, read about the shape and size of the Earth. Extremely unlikely, I know, but humor me. This hypothetical Dane would, in other words, be an extremely capable navigator and explorer.
Anyways, let's say he made his way back to Denmark and resolved to sail west past England, and discovered places like the Faroe Islands, Iceland, Greenland, and Vinland/Canada. From there, imagine that he returns to Denmark, gathers up a bunch of Danes, and makes for Vinland to set up a colony. How quickly could he sail from Denmark to Canada, without stopping? Assume he's got good weather and favorable winds, as well as a top of the line longboat for the day.
Now, for further fun, let's say this Dane established a successful colony in Newfoundland, and his son was hell-bent on outdoing his father in the exploration game. How far down the coast of North America could he conceivably make his way before he had to return to the colony for resupply?