A while back I built a Viking Longship for a cardboard boat race, with my local library. Here are some pics of the construction and the race. I'll get around to an ible eventually...
When complete it was 3 ft wide, 16 inches deep and 17 feet long, and carried four people.
I built a cardboard frame on top of a wood mold, and then glued and taped 3inch strips of card board to form the hull. Then a layer of brown paper was glued down, and a final layer of strips went on top. Seams were caulked, then the entire thing was covered with spar urethane.
Once we got the boat in the water, we discovered a big problem: 1 semi experienced and 3 inexperienced rowers don't get anywhere in a strait line. The boat was much to maneuverable for our naive rowers - we did a few 360's in the pond. We finally finished the first heat, and on the second we were doing really well... until we started filling with water. The good ship Skidbladner went under, and I the captain went down with my ship... but my life jacket got in the way. We wound up winning the Big Bertha award, longest ship finishing.
See more pics here:http://www.roundrocktexas.gov/home/index.asp?page=1413