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Author : Michael Orych
Results 1 - 2 of 2
Sailing Yacht Transom Sterns - A Systematic CFD Investigation
The question adressed in this project is whether modern hull lines with wide, box-shaped transoms, that seem
to originate from extreme racing machines, are also beneficial for modern performance cruisers from a hydrodynamic
performance point of view. A new 41 ft (12.3 m) hull was designed as an average of contemporary performance hulls in
the 40 ft segment. The aft part of the hull was stretched stepwise and cut at constant length overall in order to
systematically increase the transom size. Six hull variations with box shaped transoms were created in this way. To
investigate the influence of the transom shape, the six hull variants were redesigned with a more rounded transom. The
resistance was calculated for all twelve hulls in the upright and heeled conditions at Froude numbers 0.35 and 0.60. The
computations were carried out using a Reynolds-Averaged Navier-Stokes (RANS) solver with a Volume of Fluid (VOF)
representation of the free surface. The solver was validated against several hulls in the Delft Systematic Yacht Hull
Series (DSYHS). Very different optima are found for the low and high speed cases. In an upwind-downwind race the
round transoms performed best for the three fastest transom sizes. The fastest hull around the course has an immersed
transom area to midship area ratio of 0.16 and it has a rounded shape. It is 1.9 % faster than a more box like transom.
Overall the round transoms are faster around the race course.
Hydrodynamic Aspects of Transom Stern Optimization
In this work an explanation for an optimum transom size is proposed which takes into account the hull shape between the midship and the transom. A systematic stern modification is performed to study the influence of the shape of waterlines and buttocks on the resistance components. The aft body of a hull is designed in a way that gives a possibility to separate the effects of waterline and buttock curvature and to study their effect on the flow. The Froude numbers are chosen to provide information for wetted- as well as dry-transom conditions. To evaluate the performance of the hulls the SHIPFLOW steady state Reynolds Averaged Navier-Stokes (RANS) code with a Volume of Fluid (VOF) surface capturing method is used in combination with the k-ω SST turbulence model. The code was first thoroughly validated for a transom stern hull. The paper focuses on hydrodynamic and hydrostatic resistance components of the transom and of the rest of the hull. Physical explanations are given for the effects of the aft body hull lines. The transom size, waterline curvature and rocker effects are analysed. The results show that the optimum transom size depends on the balance between the hydrostatic and hydrodynamic force components and the explanation for this is also given.
