The copy on this website selling Viking Halloween costumes sounds like it was plucked from a middle school paper on the Vikings, and liberally sprinkled with the word "fierce."
They used Longboats which allowed them to cross open seas or sail up shallow rivers to expand their conquests. Known to be highly skilled sailors the Vikings used Longboats which had both sails and oars.
Uh huh. OK, aside from the redundancy and the terrible rhetoric, how is this supposed to make me want to buy a viking costume? It isn't like any of them come with sails and oars.
Maybe I'm supposed to think, "Hmmmm, I want to go as a seafaring barbarian for Halloween this year, but I cannot choose between one who prefers oars or one who prefers sails. Wait! Look at that! The vikings used both? You had me at 'longboats!'"
So, just remember, if you're not certain who to be for Halloween, "Dress up and be Cnut the Great who was possibly the greatest Viking King who has been nicknamed the Emperor of the North."