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Shipworms and ancient Mediterranean warships–a response
The International Journal of Nautical Archaeology (1997) 26.4: 345–346
Letter to the Editor Shipworms and ancient Mediterranean warships—a response The criticism of our article (IJNA 25.2: 104– 121) by John Coates (IJNA 26.1: 82–83) appears to consist of two separate points: the quantitative estimate of additional mass due to water of shipworm-infested ships and the practicability of the crew’s dragging a ship onto a beach. It would seem best to address each of these in turn. Above all, it should be noted that Coates appears to agree with our contention that a typical state of shipworm infestation will confer several tonnes of additional mass to a ship, an amount certainly sufficient to affect the acceleration, manoeuvrability, and general seaworthiness of a warship. As we have indicated in the article, it was our purpose to provide a realistic estimate of a maximum additional mass due to worm infestation. The actual amount for a given ship will be a function of several variables: degree of infestation, type of wood, age of ship, history of beaching time versus time afloat, and environmental factors. Historical accounts of the Perso–Phoenician fleet immediately before the engagement at Salamis suggest that its ships would have been near their maximum extent of being burdened with additional mass of water due to infestation. Certainly they would have suffered from this effect at Salamis considerably more than ships of the united Greek fleet, as we explained in our article. It had not been our intention to set exact values, since no real triremes have been found; a value for a given ship, depending upon the variables, might be as little as Coates’ figure of 2 to 3 tonnes. Nevertheless, we would point out (a) that Coates’ reported experiment dealt with a single sample of Douglas fir (a species not used in ancient Mediterranean ships) not currently infested with living Teredo and for which the degree of wormhole volume has not been quantitatively reported, (b) that the water immersion in Coates’ experiment was terminated at 16 days with the assumption that a 1057–2414/97/040345+02 $25.00/0 na970106
maximum of wood hydration had occurred based upon the observation that rate of increase of mass had diminished (it would have been preferable to verify that a maximum had been attained by continuing the process to observe an actual diminution of the rate of increase of mass to zero within experimental limits), (c) that there is an extensive body of data, cited in our article, that supports an estimate greater than Coates’, (d) that all wood and planking in the ship contiguous to the wood below the waterline will, to a certain extent, be available for shipworm infestation and/or its attendant effects, and (e) that the wood in the planking of an infested ship will consist of water, wood fibre, diminished air pockets, and the Teredo tube secretions, which consist of calcium-bearing materials. Although we did not include consideration of this effect in our publication, in order to present a conservative estimate, the fact that calcium-bearing materials in the shipworm tubes would have a specific gravity in excess of unity would be an additional contribution to increased mass in wood with dead and living Teredo. Since there have been reports that the modern ship Olympias has suffered from shipworm, it would be interesting to perform quantitative studies on it to assess the actual degree of infestation and its effects, although its use of different wood types and of modern, biocidal marine coatings, and modern modifications of the presumed ancient design would no doubt have affected the extent of infestation. As for the issue of pulling a ship onto a beach, we do agree that there are many variables to be considered such as slope, condition and nature of the terrain, and characteristics of the vessel. The commanders of the ships would have been experienced in selecting likely beaching sites. In the case of the Greeks, the commanders and crews may well have had firsthand knowledge of favourite sites. We would point out that the idea of an able-bodied crew ? 1997 The Nautical Archaeology Society
NAUTICAL ARCHAEOLOGY, 26.4
member dragging 100 kg, the mass of a moderately large man, a distance of several metres over an appropriate surface does indeed seem reasonable. The ability of a man to thrust 100 kg with his legs is indisputable—author AGS can do this. It would be most interesting to explore the mechanics of beaching on undeveloped beaches vis-a`-vis pulling a ship onto greased timber groundways, as suggested by Coates, at such time as archaeological or historical evidence of such constructions becomes available.
346
Alwin G. Steinmayer, Jr. 558 Leopard Street, Berwyn, Pennsylvania 19312, USA Jean MacIntosh Turfa Department of Classical and Near Eastern Archaeology, Bryn Mawr College, 101 North Merion Avenue, Bryn Mawr, Pennsylvania 19010-2899, USA
Letter to the Editor Shipworms and ancient Mediterranean warships—a response The criticism of our article (IJNA 25.2: 104– 121) by John Coates (IJNA 26.1: 82–83) appears to consist of two separate points: the quantitative estimate of additional mass due to water of shipworm-infested ships and the practicability of the crew’s dragging a ship onto a beach. It would seem best to address each of these in turn. Above all, it should be noted that Coates appears to agree with our contention that a typical state of shipworm infestation will confer several tonnes of additional mass to a ship, an amount certainly sufficient to affect the acceleration, manoeuvrability, and general seaworthiness of a warship. As we have indicated in the article, it was our purpose to provide a realistic estimate of a maximum additional mass due to worm infestation. The actual amount for a given ship will be a function of several variables: degree of infestation, type of wood, age of ship, history of beaching time versus time afloat, and environmental factors. Historical accounts of the Perso–Phoenician fleet immediately before the engagement at Salamis suggest that its ships would have been near their maximum extent of being burdened with additional mass of water due to infestation. Certainly they would have suffered from this effect at Salamis considerably more than ships of the united Greek fleet, as we explained in our article. It had not been our intention to set exact values, since no real triremes have been found; a value for a given ship, depending upon the variables, might be as little as Coates’ figure of 2 to 3 tonnes. Nevertheless, we would point out (a) that Coates’ reported experiment dealt with a single sample of Douglas fir (a species not used in ancient Mediterranean ships) not currently infested with living Teredo and for which the degree of wormhole volume has not been quantitatively reported, (b) that the water immersion in Coates’ experiment was terminated at 16 days with the assumption that a 1057–2414/97/040345+02 $25.00/0 na970106
maximum of wood hydration had occurred based upon the observation that rate of increase of mass had diminished (it would have been preferable to verify that a maximum had been attained by continuing the process to observe an actual diminution of the rate of increase of mass to zero within experimental limits), (c) that there is an extensive body of data, cited in our article, that supports an estimate greater than Coates’, (d) that all wood and planking in the ship contiguous to the wood below the waterline will, to a certain extent, be available for shipworm infestation and/or its attendant effects, and (e) that the wood in the planking of an infested ship will consist of water, wood fibre, diminished air pockets, and the Teredo tube secretions, which consist of calcium-bearing materials. Although we did not include consideration of this effect in our publication, in order to present a conservative estimate, the fact that calcium-bearing materials in the shipworm tubes would have a specific gravity in excess of unity would be an additional contribution to increased mass in wood with dead and living Teredo. Since there have been reports that the modern ship Olympias has suffered from shipworm, it would be interesting to perform quantitative studies on it to assess the actual degree of infestation and its effects, although its use of different wood types and of modern, biocidal marine coatings, and modern modifications of the presumed ancient design would no doubt have affected the extent of infestation. As for the issue of pulling a ship onto a beach, we do agree that there are many variables to be considered such as slope, condition and nature of the terrain, and characteristics of the vessel. The commanders of the ships would have been experienced in selecting likely beaching sites. In the case of the Greeks, the commanders and crews may well have had firsthand knowledge of favourite sites. We would point out that the idea of an able-bodied crew ? 1997 The Nautical Archaeology Society
NAUTICAL ARCHAEOLOGY, 26.4
member dragging 100 kg, the mass of a moderately large man, a distance of several metres over an appropriate surface does indeed seem reasonable. The ability of a man to thrust 100 kg with his legs is indisputable—author AGS can do this. It would be most interesting to explore the mechanics of beaching on undeveloped beaches vis-a`-vis pulling a ship onto greased timber groundways, as suggested by Coates, at such time as archaeological or historical evidence of such constructions becomes available.
346
Alwin G. Steinmayer, Jr. 558 Leopard Street, Berwyn, Pennsylvania 19312, USA Jean MacIntosh Turfa Department of Classical and Near Eastern Archaeology, Bryn Mawr College, 101 North Merion Avenue, Bryn Mawr, Pennsylvania 19010-2899, USA