Marine Technology - October 2007 - Page#90

<BODY> <span id="lblContents">added on top of the rocks to smooth the surface where the cargo was to be laid). The cargo aboard this Nau consisted mainly of pepper, weighing between 3,000 and 5,000 quintais (1 quintal equals 58.75 kg), as indicated by Castro (2005a). Costa (1997) indicates some cargo weights for ships returning from India, and 4,500 quintais (265 t) is a usual cargo weight for ships of this size. The available volume in the hold above the ballast can be found to be 606 m3 and, taking into account that the pepper density can be estimated to be 0.5 kg/dm3, the volume required for the 4,500 quintais is 530 m3. This indicates that the estimated cargo of pepper could be carried entirely in the lower hold, which is according to the loading scheme described by Falc?o (1607). The center of gravity of the pepper can be estimated to be located 19.6 m forward of the aft perpendicular and 2.83 m above the baseline. These results indicate that the lines plan derived from the archeological remains and contemporary shipbuilding treatises is plausible, given that the estimated ballast and cargo can indeed be accommodated inside the hold, as prescribed in Falc?o (1607). Table 4 Center of sailing areas Sail Mizzen sail Main sail Main topsail Fore sail Fore topsail Spritsail Total Zg center of mass Area (m2) 226 325 557 332 225 124 1,789 Zg (m) 22.3 35.0 19.0 19.0 32.4 20.3 24.0 5. Estimation of the loading conditions The analysis of the floatability and stability of any ship requires knowledge of both the ship's geometry and the ship's mass and center of gravity. The estimation of these properties for an early 17th century ship, whose geometry and constructive details are not known accurately, represents a major task and one bound to yield a result with some uncertainty. Furthermore, as usual, a considerable number of loading conditions are possible. In this study, the loading condition at the departure from India for the return voyage was selected because the ships tended to be severely overloaded, and this appears to have caused a considerable number of losses around the turn of the 16th to 17th centuries, especially in the area of the Cape of Good Hope. The arrival condition is also considered since it is of interest to evaluate the ship's stability at the moment of the accident. The weight of the ship has been subdivided in a number of components: hull, masts and yards, sails, rigging (shrouds, etc.), anchors and ship's boats, artillery, ballast, cargo, crew, soldiers, passengers, and supplies. The hull of the ship, shown in Fig. 8, has been estimated to weigh 398 t according to the hull structure description given by Castro (2001). An extensive list of components, comprising the hull planking, decks, and structure, was identified together with their individual weights and positions of the center of gravity. The various types of wood employed in the different structural elements were also considered. The hull's center of gravity has been estimated to be located 18.0 m forward of the aft perpendicular and 5.9 m above the baseline. The weight of the masts and yards has been estimated by Castro (2005b) at around 26 t by calculating the volumes of wood involved in each component and considering the specific weight of the wood to be 0.52 t/m3. Taking into account the dimensions given in Fig. 9, the center of gravity of the mast and yards can be estimated to be located 20.25 m forward of the aft perpendicular and 19.45 m above the baseline. The weight of the sails, corresponding to the sail plan shown in Fig. 10, was calculated by taking the total area of the sails (1,789 m2) and multiplying it by 1.0 kg/m2, resulting thus into 1.8 t. The areas and centers of mass of the various sails are shown in Table 4. The sail plan of Fig. 10 has the center of gravity located 22.5 m forward of the aft perpendicular and 24.0 m above the baseline. Furthermore, two sets of sails were considered to be carried onboard, resulting in a total weight of 3.6 t. OCTOBER 2007 The rigging of the ship was estimated to weigh 5 t, as a rough estimate. The location of its center of gravity is obviously very difficult to find, so it was assumed that it is located at the same location as the center of gravity of the sails. The anchors carried by a ship of this type are, according to the documents presented by Domingues (2004), four anchors weighing 17 quintais each and four anchors weighing 16 quintais each, with a total weight of 7.8 t. The corresponding anchor lines weighed approximately 10.2 t. Both these weights were usually carried inside the forecastle and were assumed to be located at 36.5 m from the aft perpendicular and 9.5 m above the baseline. The ship also carried two small boats called batel and esquife weighing around 10 t. These were assumed to be located at the center of the main deck, between the two castles, 24.0 m from the aft perpendicular and 8.5 m above the baseline. The artillery carried in this ship is not known, but Domingues (2004) presents several documents detailing the artillery carried by the Nau type of ship, which is given in Table 5. The artillery was subdivided into 21 heavy weapons and 16 light weapons, with a total estimated weight of 34.9 t. Ships of the galleon type were generally better armed, but Nossa Senhora dos M?rtires was a merchant ship. The ammunitions for these weapons can be estimated to weigh 3 t, and the gunpowder carried onboard weighed approximately 0.5 t. The 21 large guns, one of which is shown in Fig. 12, were located in the main deck, with the aggregated center of gravity located at 20.0 m forward and 6.90 m above the keel, while the lighter guns were carried in the main and upper decks, 20.0 m forward and 9.5 m above the baseline. Castro (2001) estimates that this ship could carry a crew of 150 men and 230 soldiers. Furthermore, 75 passengers could also be onboard. Each men of the crew or soldier could have weighed 60 kg and carried baggage weighing 20 kg. The passengers could have carried 100 kg each and weighed the same as the crewmembers. The total weight of the crew, soldiers, and passengers (plus their baggage) was then 42.4 t. The passengers made the voyage in the poop deck, quarterdeck and some of their baggage in the main deck. The center of gravity of the passengers and their baggage can be estimated to be located 8.0 m forward and 9.3 m above the baseline. The crew and their baggage were located in the lower Table 5 Artillery of a 600 toneis Nau Type 1 camelo 12 esperas 8 pedreiros 10 falc?es 6 ber?os Total Weight (quintais) 30.0 25.0 13.0 7.5 1.8 519.8 Zg (m) 6.9 6.9 6.9 9.5 9.5 --? center of mass Note: One quintal is equivalent to 58.75 kg. Zg MARINE TECHNOLOGY 261</span> <br /> <br /> <a href="http://www.digitalwavepublishing.com/" title="Digital Magazine">Digital Wave Publishing</a> </BODY>