Viking ship tackling the wind
The civilian trade ship was called knarr.
The long ship was relatively shallow going (allowing for rapid deployment on sandy shores), sporting a rectangular sail and oars along almost its entire length. Oftenmost longships were clinker built, and waterproofed by moss drenched in tar.
Our best evidence for longship construction comes from ship-burials. It was common in Viking society for kings to be buried under a long burial mound in a ship with rich possessions. The Viking Oseberg[?] ship burial in Norway and the Anglo Saxon longship of Sutton Hoo in England are both good examples.
Longships really were long, and narrow - quite extremely so. The largest discovered longship (at Roskilde harbor) is 35m in length, and the longship from Hedeby harbour has the largest length/width proportion: 11.4 to 1.