The history channel had a show called the Big Build tonight where
they built a small viking longboat using spoke shaves and hand planers etc.
Good show, i could relate with all of the build.

It was interesting, that they used wool soaked in pine tar to fill the gaps between planks and stated it would last the life of the boat is as good if not better than caulk.

Also..they used pine tar to coat the bare planks.