More background on ships
Comments from a few other books fit well with the previous post Background on Viking Age – ships for warfare, travel, and cargo – 4 of 5
Vikings: Raiders, Traders, and Masters of the Sea by Rodney Castleden, provides more explanations of ship types, starting on page 111.
When thinking of Vikings crossing the sea, we tend to think of them using those famed longships. Those were used on raids because they were so fast and with their shallow draft could beach on the shore or go far upstream.
For long distance travel, Vikings would use a knarr, also called a hafskip. A knarr used a sail for power with the few oars being for maneuvering. A longship had both sail and many oars. A longship had low free board and a knarr or hafskip had high free board. Free board is the distance between the deck of a ship and the waterline.