Writing a fantasy series does lead one down some intersting research paths. Today, as I was writing, I had to stop and figure out how my main characters would decide how big of a ship they needed. This led me to learn this interesting fact.
King Edward, I of England was the first to place a tax on ships. At that time, it was calculated on each “tun” of imported wine (a tun being 252 gallons and weighing about 2,240 pounds or just over 1,000 kilograms in today’s measurement). In those days, the carrying capacity of a ship was based on “tonnage”, calculated by multiplying the length of the ship by the beam (width) and then multiplying the result by the depth. The resulting number was then divided by 100 to calculate the area available for cargo, known as the tonnage.
This held sway until 1678 when a new method was introduced by shipbuilders on the Thames River. This calculation, which is too complex to write here, assumed that the cargo capacity was actually only 3/5’s of its displacement.
This new formula and various derivatives held sway until the coming of steamships in the mid-1800s.
Now, I have to get back to work. I have a tun of work to do (or is that ton)?
Paul Bennett, Writer of Epic Fantasy Stories.