Friday, January 02, 2004

Estimating Gross Tonnage for English and Dutch ships I started, last night, the process of learning the AOSII Privateers Bounty (game from Akella) scenario editor. Creating ships is quite easy. I have a spreadsheet that I use to do the calculations, as I need to calculate the "Hull" and "Depth" numbers. The "Hull" is actually the burden, calculated in English units. The formula is: Burden (in tons) = LK * B * B / 188 where LK = length on the keel B = beam outside the planking. (For purists, you would write the formula as: Burden = LK * B * (B/2) / 94 The difference is that the B/2 is a nominal depth. For whatever reason, the English eliminated a true depth in hold from the calculation. Earlier tonnage calculations used a true depth. The Dutch equivalent, the (non) calculation for "lasts" actually uses the depth in the hold: Lasts = L * B * D / K L = length from stem to sternpost B = beam inside the planking D = depth in hold, measured to the deck edge, not the center of the deck. This ignores the deck camber in the calculation. K = a factor that, sadly, was not fixed. This makes this calculation not very useful. In reality, "lasts" figures were estimated, so that causes the factor to be wildly variable. Still, if you want to be able to estimate size of ships (contrary to Ab Hoving's advice), you are forced to deal with this. Generally, "lasts" are rounded, so you have figures like "300 lasts" or "150 lasts". In reality, based on known figures for the mid-17th Century, we can fairly reasonably estimate ship sizes. The best we can do are estimates, but they are not that bad: Heemskerck, Abel Tasman's ship, built in 1638 (thanks to for this information) Length: 106 feet Beam: 24 feet Hold: 9 feet Let's start by using an initial estimate for K=237 Lasts = 106 x 24 x 9 / 237 = 96.6 From this, I suspect that the right nominal lasts number is 100, so we adjust K, accordinly: Lasts = 100 = 106 x 24 x 9 / K K = 106 x 24 x 9 / 100 K = 228.96 From this, you can follow my method. Now, let's estimate the depth of hold for the Noorder-Kwartier ship, the Eenhoorn. The Eenhoorn has been called the patriarch of Dutch ships during the First Anglo-Dutch War (I believe by Dr. Elias). From the "Staet van Oorlogh te water voor den jaere 1654", we know the length and beam (125 feet and 29 feet, respectively). We also know that the ship was usually estimated as 200 lasts (I believe that a 1628 list gave a figure of 220 lasts). Again, I use an initial estimate for K = 237. 200 lasts = 125 x 29 x D / 237 D = 13 feet Revised K = 235.625 As a matter of interest, we know the Eenhoorn's armament in 1654: 7-12 pdr 13-10 pdr 4-8 pdr 2-6 pdr 2-4 pdr 2-3 pdr As you can see, the Eenhoorn was armed with "odds and ends". We might imagine that ammunition supply might have been a challenge, with so many calibers.

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