Drag coefficient with aspect ratio calculator skin#
Skin friction is based on the friction between the water and the shell. Form drag is a force proportional to the square of the boat speed that depends on a drag coefficient which incorporates area of the shell and density of water. With regards to the kinetics of a shell, three categories of retarding hydrodynamic forces act on it form drag, skin friction, and wave drag. This theory is used as the basis of the experimental analysis. Since these largely accepted ratios for planing hydro craft do not strictly apply to racing shells, it is important to define the dynamics that impact the shell.
This value can loosely be used to relate under water volume of a shell to the length and maximum beam area. With regards to long, thin displacement hulls, the prismatic coefficient tends to approach 0.7. When the speed length ratio applies, the volume of a hull can be designed under guidance of the C p to support the shells speed at a corresponding speed length ratio. The prismatic coefficient, C p, is the ratio of the volume of displaced water to the maximum area times the length of the water line. However, as stated prior, these naval architecture principles are not reliable for long, thin, displacement hulls. This would be an answer to the frequently disputed question of how shell length affects speed. If it is assumed that a racing shell applies to this principle and has a SLR of 1.3, it can be said that as water line length increases, maximum potential speed increases as well. A hull with a SLR of around 1.3 is in displacement mode, 1.3-2.5 is semi-planing, and 2.5 and above is fully planing (Sponberg 2010). This ratio applies to craft that transition from displacement to planing hulls, and is not directly applicable to a racing shell. Similarly, the effect of wind and current on the drag coefficient could be analyzed as well. This is a limitation that was implemented so as to avoid the requirement to include theoretical approximations and maintain purely experimental results. It is noted that the drag coefficient defined in this study does not seek to isolate hydrodynamic and aerodynamic drag. As such, the drag coefficient defined in this study is limited to an experimental approximation. While certain resources, such as shell and rower availability, were commodities, funding, time and environmental conditions were not. That is, the testing procedure outlined in this study can be run on a shell to obtain a preliminary drag coefficient, at which point a design change would be made to the shell, and the test would be re-run to identify how the drag coefficient was changed. The aim of this study is to define a method of testing a racing shell to determine a universal drag coefficient. It is the lack of prior research that gives this study value. Previous research, supposedly conclusive, has been conducted on large shells for the US National Team, though the details of this study have not been made public. It is noted that no other public data was found on eights. It is with great fortune that the University of Delaware Men’s Crew Team was able to be used as a resource, as data could be obtained on 8+ racing shells.
Of these studies, it is noted that none included an experimental analysis of a large shell, presumably because of the lack of availability of eight-man boats (known as an 8+).
The aims and results of these studies are taken into consideration in this project. There are a number of studies on the biomechanics of the rowing motion, but few that deal directly with the shell design (Baudouin & Hawkins 2010), (Day et al. Though there has been research conducted on racing shells in the past, the knowledge base is rather limited. Because of this principle, the sailboat with the design most similar to the racing shell is the catamaran, both of which have long, thin hull shapes.īecause of the principle differences between a racing shell and standard planing hydrocraft, specifics regarding the dynamics of a racing shell are frequently disputed. That the racing shell is a displacement hull, that is, it is supported primarily through buoyancy rather than lift, is its main deviation from standard yacht designs. While certain aspects of these basic naval architecture principles loosely apply to a racing shell, they do not explicitly define the mechanics of the shell. Some of this theory can be seen in the Theoretical Background. Much of the knowledge regarding hydro craft of such a nature surrounds Yachts and the Americas Cup. In the sport of rowing, scientific research on racing shells is limited due to the relatively small community and the lack of funding.
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