The comparison was for size, as stated, to show just how large the Viking vessel was. And it was just one of many. Svein Forkbeard (Canute’s father) spent about 20 years building barracks, training men, and laying keels to prepare for the invasion.
The Vikings, friendly merchants from the North.......
“You cut off John’s head!!!”
“That’s one of our business strategies.”
We should also keep in mind that in 1066 AD, Viking conquerors/settlers of northwestern France( AKA the Normans (Norse men)) under William essentially used this same knowledge to organize and execute the only successful cross channel invasion of the British Isles to date.
To be fair, the Saxons were a bit thin on the ground at Hastings, having just force marched down from eastern England where they met and destroyed an earlier invasion of Vikings (this time from Norway)at Stamford Bridge.
Wikipedia has a short article on the battle for the bridge and how it interplays with the Battle of Hastings 3 weeks later:
http://en.wikipedia.org/wiki/Battle_of_Stamford_Bridge