Here (above) is a photo showing part of a page from an original copy of the Greenland/Vinland Saga.
Here (above) is a map showing where L'Anse aux Meadows. Comparing the distance of sailing back to Norway with sailing down the coast of what would eventually become the USA makes Vikings in New Hampshire seem possible.
The boat-types used by the Norse were quite varied, depending on what the ship was intended for, but they were generally characterized as being slender and flexible boats, with symmetrical ends and with a true keel. They were clinker built, which is the overlapping of planks riveted together. This design was extremely versatile and allowed the Vikings to travel far from their Scandinavian homeland, to Iceland, the Faroe Islands, Greenland, Newfoundland, the Mediterranean, the Black Sea and Africa.
In my opinion a successful Viking journey to the seacoast of New Hampshire is not farfetched at all. So long as the travelers had fair weather, provisions, and crew enough to handle the job efficiently there is no reason to believe that it was not possible. For now it’s just theory but who knows maybe someday a bit of archaeological proof will surface which will officially place the Vikings in New Hampshire.