Saxo's Danish History, Book 8 Part 2

"Thorkill did not refuse the task, and advised that, to meet the extraordinary fury of the sea they had to cross, strongly-made vessels should be built, fitted with many knotted cords and close-set nails, filled with great store of provision, and covered above with ox-hides to protect the inner spaces of the ships from the spray of the waves breaking in. Then they sailed off in only three galleys, each containing a hundred chosen men."

"And when these men saw that they were constrained, and could not possibly avoid the peril, they covered their ship with ox-hides, and filled it with abundant store of provision."
http://www.sacred-texts.com/neu/saxo/saxo082.htm

Does it sound like they're covering part of the ship or the whole ship? With a hundred men per ship, those would be pretty big ships to cover.

Most likely they were just stringing the hides between the rafters of the ships - that is making a cover over storred goods at the level where we would find the deck of a modern ship. In fact, given that most of the ships were a single open space with no crossing beams, it could be necessary for the men to actually use it as deck if they were as crowded as the text indicates. But there were different boats for different purposes and waters in Scandinavian back then.
Though the image that most likely comes to mind when reading this passage is that of rather slim longboats with shallow draft, one has to remember that oceangoing vessels like the boattype 'knarr' is what would have being used when sailing the rough North Atlantic. This is a much fatter and sturdier boat with much less surface to volume ratio than the more known (and copied) war ships.
For comparison look at this exhibition: http://www.vikingmagasin.dk/vikinglex/skuldelevskibene.htm
The boat the the left/foremost is a knarr and the ones to the right/background are warships as commonly known.
Reconstructions of this knarr can carry in the order of 17 tons of netcargo - as compared to the only 6 tons of the longer warship, though this incidently would haved been crewed by 80-100 men. Not exactly large and luxurious boats by our standard.
It could have been the large longboats h¨they used instead, but in either case the usual way to cover any goods carried would be stringing the hides over those at a low level rather than errecting any sort of largescale tentlike structure over the entire boat. Plus the goods had to be kept firmly in place even if the boat bucked and rolled from wavecrest and into deep throughs. If there was room for the men too, this would only have been very limited, in the form of a narrow space ontop of lashed bales of what else the ships had to carry. Those were the days of basically open boats with saltspray howling into the face of those aboard - in storms you either stayed ashore or had to ride it out at sea with plenty discomfort.

In either case Saxo Grammaticus is not necessarily the most authorative source on detail from centuries before his own time. Basically all he had to work from was oral legend and some sagas. His primary goal would have been setting the scene for events which were unfoulding in his own age, not scientific research as we know it. Nonetheless great reading at times, if only for the tales he has to tell!

I figured they must be the knarr type because of the mention of "great store of provisions", and that these were voyages of exploration. I have a couple of books on vikings and they both have these boats with half-decks fore and aft. I just wasn't clear on what was being covered, men or goods, or both.