Engineering analysis of 19th century British merchant ships

Abstract

Previous analysis of the evolution of 19th Century British merchant ships has been primarily qualitative. This research aims to develop a method to quantitatively analyse historic ship performance and to challenge present conceptions of ship design in the 19th Century. Literature indicates that this was a period of change, with the transformation from wooden sailing ships to steel steam ships. A parametric study of existing hull data demonstrates the potential to carry out a diachronic study of changes to ship design and performance. However, there is insufficient data to draw conclusions on performance factors such as ship speed. This is countered by the creation of a new dataset, based on a velocity prediction program (VPP) designed to calculate the sailing performance of historic ships. With few examples of these vessels remaining, the VPP must work with minimal input data. Regression-based methods used in initial ship design have therefore been identified and validated using CFD, forming the basis of the VPP. The input data comes from lines plans and builder’s half models from maritime museums around Britain. With the correct methodology, a large amount of information can be extracted from these sources. Tests show that 3D scanning of half models can be used to create a lines plan, which can be converted into digital models. This allows a new set of hull data to be generated. Where available, sail plans are used to calculate sail areas, with regression lines to provide estimates where there is no sail plan. Weights and centres are estimated in a similar way based on survey reports. 61 British ships from throughout the 19th Century were digitised. The parameters extracted are used to generate a set of speeds under different conditions using the VPP. A second parametric analysis was carried out with the new data, enabling narratives to be visualised where it was previously impossible. This shows that advances in performance were driven by hull form, and the historic understanding of hydrodynamics and its impact on design may be traced. Comprehension of the evolution of these ships has also been challenged. Tonnage laws are often credited with causing changes to hull form and performance, but the data indicates that any effect they had was more gradual and less than previously suggested. The same appears to be true for the repeal of the Navigation Acts, as British ships had been gradually improving prior to this. The view of different ship types is also questioned. The dataset indicates that East Indiamen, often treated as obsolete, were capable of reaching speeds equal to some ships of the 1850s. It is also shown that average windjammers had greater capacity and upwind sailing performance than clippers. The understanding of the evolution of 19th Century British merchant ships has been advanced by the creation of a new methodology for determining the performance of historic ships. Along with the generation of a new dataset, this provides a fresh view of a topic that has been extensively commented on qualitatively and can now be analysed quantitatively.

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