The Vikings are back

Not the movie, but a crew who have reconstructed a longship and intend to sail it from Denmark to Ireland. The ship is called the Sea Stallion and it will be launched tomorrow. The Sea Stallion has an attractive website which you can use, among other things, for following its progress.

Question: Vikings could be either merchants or pirates, and usually both. This applies to just about every sailor of ancient or medieval times. Very little "Law of the Sea" back then. Is there a good book about this?

Image: The Sea Stallion's first launching, 2004.