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Prehistoric trade between Ecuador and West Mexico: a computer simulation of coastal voyages ,
Richard T. Callaghan
The author studies prehistoric sea travel along the coast between West Mexico and Ecuador using a computer simulation incorporating the performance characteristics of sailing rafts. The model predicts that while northward voyages may have taken as little as two months, southward voyages would have entailed at least five months and may have required a strategy that took the rafts offshore for as long as a month. Keywords: West Mexico, Ecuador, trade, sailing rafts, navigation A variety of evidence shows that contact occurred between Ecuador and West Mexico (Figure 1) from 400 BC to the sixteenth century, even if such contact was not necessarily continuous. The evidence comes from metallurgy (Hosler 1988; Hosler et al. 1990), shaft tombs and mortuary offerings (Kan et al. 1989), ceramic technology and style (Piña Chan 1989:33-38), language (Swadish 1967), design motifs (Meighan 1969), ethnographic sources (West 1961), costume (Anawalt 1992), and a number of other features (Zevallos 1987), and indicates that contact occurred sporadically from 400 BC to 400 AD, and around 800 AD, 1200 AD, 1300 AD, and 1600 AD (Anawalt 1992). Computerised simulation programs have been used to investigate a number of archaeological and historical problems, including population dispersals (Levison, Ward & Webb 1973; Thorne & Raymond 1989), exploration strategies (Irwin et al. 1990), population origins (Callaghan 1999; 2003a), maritime trade and interaction (Callaghan 2001) and trans-Pacific contacts between Japan and North America (Callaghan 2003b). A computer simulation designed to answer various problems relating to prehistoric and historic voyaging is used here to investigate the difficulty of maintaining contact between Ecuador and West Mexico and to determine the level of skill necessary to make these trips safely
The simulation program used here is a much more advanced version of the one used in Callaghan 1999 and 2001. This second-generation program is based on the United States Navy Marine Climatic Atlas (US Navy 1995) and has been expanded to include all of the world’s seas and oceans with the exception of Arctic waters. The data is organised in a finer resolution of one degree Marsden squares (one degree of longitude by one degree of latitude) rather than two degree Marsden squares. In particular, this allows the effects of smaller and more variable currents to be accurately reflected in the outcomes. The advanced program also automatically shifts to the database for the following month after the month originally selected for has expired. This feature better reflects the reality of changing wind and current conditions over long voyages. A conversion to spherical co-ordinates has also been added in order to increase positional accuracy outside of the tropics. Finally, the program allows the operator to change the heading of a vessel during a voyage to reflect decisions made by the crew. This last feature is important when assessing the level of skill required to reach a selected target. In its basic operation, the program makes a random selection of direction and speed for wind and current from the Marine Climatic Atlas (US Navy 1995) database. These data are compiled from ship reports and other sources since the early nineteenth century. A course is chosen for the vessel, unless undirected drift voyages are being investigated. Performance data, calculated using either naval architecture programs or field tests, are then used to calculate the ratio of vessel velocity to true wind velocity. Wind and current forces are allowed to affect the vessel for a twenty-four hour period, and a new position for the vessel is then calculated. A new heading is chosen every twenty-four hours to move the vessel in the desired direction
Watercraft The results of extensive research conducted by Clinton Edwards (1965a, 1965b, 1969, 1978) indicate that sailing rafts, sailed canoes, and paddled canoes were likely to have been used by Ecuadorian merchants during the period under consideration. Sailing canoes, which would have been more effective than paddling over long distances, appear not to have been adopted Richard T. Callaghan in northern Ecuador until the time of Spanish contact in the early part of the sixteenth century (Edwards 1965a: 356). Unfortunately, as Edwards points out, there is little archaeological evidence that suggests a preference for any of these watercraft in any possible prehistoric trade with West Mexico. Most of the pertinent data is from ethnographic and historical sources. However, given the lengthy distances involved in this problem, over 1800 nautical miles (c. 3450 km) in a straight line, and given that sailing rafts are safer, more comfortable, and capable of carrying larger cargoes than dugout canoes (Doran 1978; Edwards 1969: 8), they were chosen for this voyaging simulation. Zevallos (1987: 17-25) argues the balsa sailing raft is of indigenous Ecuadorian invention and that it was in use for trade to the north and south by Valdivia times (c. 3000 BC). Sailing rafts appear to have had a distribution from the Sechura Coast of Peru to the Manabí coast of Ecuador, and possibly as far north as Cabo de Galera (Edwards 1969:4). Both the sails used on these rafts at the time of European contact and the dagger boards used to steer them are clearly of aboriginal design, one foreign to Europeans (Edwards 1965b: 66-81). These dagger boards are positioned between the logs of the balsa raft and are raised or lowered in order to steer the craft and balance the sail (see Estrada 1988; Baleato 1988). The size of the rafts varies considerably, from small fishing craft capable of being used as “lighters” carrying cargo of up to half a ton between vessels and shore, to large merchant craft carrying 60 to 70 tons of cargo. Historic records show these craft sailing from Guayaquil to Lima in the south and from the same point to Panama in the north. These are distances of over 600 nautical miles (1100 km). The southward voyage to Lima reportedly took two months. This would have been the more difficult of the two voyages, as the rafts would have been sailing against both wind and current no matter what the time of year. Prehistoric pottery recovered in the Galápagos Islands has been identified as being 90 per cent originating on the Ecuadorian coast (Holm 1988: 184-185). The Galápagos Islands are 522 nautical miles (840 km) from the South American coast well out of sight of land, suggesting some knowledge of oceanic navigational methods. Modern replicas of balsa sailing rafts have sailed from Ecuador to within 400 nautical miles of Australia (Estrada 1988: 347).
However, the origin of the sailing rafts used in northern Peru and Ecuador is the subject of some controversy. Their distribution in the Americas is very restricted, while sailing rafts with very similar attributes, such as steering mechanisms and other features, are widespread in south-east Asia, and south-east China (McGrail 2001: 264, 294 and 351). Many scholars believe that the sailing raft was introduced to South America from Asia, a point of interest that has less impact on this research than does the striking similarity in the design and the operational features of the sailing rafts used in Ecuador and those used by Taiwanese fishermen. Doran (1978) constructed a replica of the Taiwanese sailing raft and calculated its sailing performance for varying angles to the wind (Figure 2). Given the close similarity of the South American and Taiwanese craft, the sailing performance figures for Doran’s replica have been used here
Thirty voyages were simulated using this strategy. The shortest durations necessitated a departure between February and April. Voyagers could stay inshore as far as Guatemala, reaching it in about 65 days. From there, a short, week-long trip out to sea brought them back to land near the current location of San Salvador. It was possible to stay inshore for another week before heading out to sea just north of Fonseca. Vessels had to sail southward for about 260 nautical miles (480 km) and then east for 300 nautical miles (450 km) making landfall at the Nicoya Peninsula after about thirty days. From there, coastal sailing was possible to the Azuero Peninsula, which could be reached in roughly three weeks. A final, two-week excursion into the open sea would bring the voyagers home to the Manabí coast. The necessity of sailing out to sea, beyond any possibility of sighting land, suggests some form of oceanic navigational method was known to Ecuadorian voyagers rather than a total reliance on visual pilotage. This is also suggested by archaeological recoveries from the Galápagos Islands (Holm 1988). Northward sailing is thus a relatively easy task, while southward sailing is a lengthy endeavour requiring considerable navigational skills. Given the difficulty of the return trip, the main trade item sought must have been very valuable. Ecuadorian traders supplied Spondylus shells to the huge market south of their lands (Norton 1988). Spondylus was used for ritual purposes and this item was highly valued and considered essential. The mollusc does not occur in the colder waters to the south, and its distribution in areas north of Ecuador is sporadic. It is found in the area around Jalisco. These lengthy expeditions (on the order of a year and a half in duration) probably only took place when Ecuadorian and other nearby sources were depleted