When Danes invaded Anglo-Saxon England they used longships. These ships seemed to have one deck with no living quarters. The journey from Denmark and other Nordic nations to England must have lasted some time. Did these warriors simply live together on the deck without shelter from the elements?
I answered a similar question here before. But the basic answer is:
It's not far at all from Norway/the other Scandinavian countries to Britain. You can sail from say Bergen to London in about four or five days, and that wouldn't be a direct route for the Viking invasions anyhow; they were landing in the northeastern part of what's now England, though they certainly raided along the coast and into the Irish Sea.
We're not entirely sure if they raided only using longships, or sailed in that type of ship most of the time. We honestly don't know much about Viking ships archaeologically; we have the Gokstad ship, and Oseberg ship, and the Skuldelev wrecks (which aren't longships). The Gokstad and Oseberg ships are very close both geographically and temporally, so they may or may not be representative of what ships were like at the time.
We know from sources like the Anglo-Saxon Chronicle that there were several different ship types in northern waters. But the records we have of this are fragmentary. From that answer:
The thing is, though, that we don't know how exactly they looked, and there were at least three different shipbuilding traditions at work in the North Sea. We know this because the Anglo-Saxon Chronicle says that "King Alfred had long ships built to oppose the [Danish] warships [lang scipu ongen ða aescas]. They were almost twice as long as the others. Some had 60 oars, some more. They were both swifter and steadier and also higher than the others. They were built neither on the Frisian nor the Danish pattern, but as it seemed to him himself that they could be useful." (Quoted in Rodger, Safeguard of the Seas pp. 15).
(As a sidenote: It's quite possible that "him himself" literally means that Alfred designed these himself; he was both a carpenter or at least familiar with carpentry and a seafarer.)
So the author(s) of the ASC were aware of at least three different shipbuilding traditions going on around England (the ships Alfred had built, the Frisian and the Danish ships). The Danish ships were probably warships, the Frisian ships were probably traders, and the English ships were built to counter the Danish ships. If they were in fact 30-room ships (with 60 oars) they would have been quite large for the time, with probably 2-3 times the crew of a 20-room ship.