Comparison of modern keel types for sailing yachts

Have you ever reflected over the different types of bulbs chosen for yacht keels? Today there is no general agreement on which bulb type is preferred for different types of yachts and very little scientific investigation has been done in this area. SSPA and Chalmers have carried out a study, where the hydrodynamic performance of different types of bulb keels were systematically evaluated. A paper is published in the International Journal of Small Craft Technology (IJSCT), a RINA Publication.

Have you ever visited a boat show or a boat yard at winter and reflected over the different types of bulbs chosen for the yacht keels. There is no general agreement today on which bulb type is preferred for different types of yachts and very little scientific investigation has been carried out for bulb keels for production yachts. Most of the scientific investigations for keels that has been carried out has been related to racing yachts such as America’s Cup and Volvo Ocean Race. In order to shed some light on the subject, Chalmers University of Technology and SSPA carried out a study, where the hydrodynamic performance of different types of bulb keels were systematically evaluated. 

Four different keels were evaluated (3 bulb keels and one standard fin keel as reference) in a wind tunnel and further studied in a velocity prediction program (VPP). Two different scenarios were investigated in the VPP; new design and keel retrofitting. The selection of the shape and weight of the bulb for a sailing yacht keel should be carried out at an early phase of the design of the yacht. This is so, since the righting moment from the keel will influence the choice of rig and sails. In case the yacht already is built/designed and the keel is retrofitted, the sail and rig is already set and thereby the whole yacht is not as optimised as if it was designed from the beginning.

The results shows that the differences between the bulb keels are small, but the keel with a bulb integrated with the fin is slightly slower than the keels with more distinct bulbs, in either L- or T-configuration. These are very close in retrofit, but the T-configuration has a slight advantage in the new design scenario.

About the paper

The paper; “Comparison of Modern Keel Types for Sailing Yachts”, published in RINA, Vol 159, Part B2, International Journal of Small Craft Technology, Jul-Dec 2017. Co-authored by Kasper Ljungqvist, and Christian Finnsgård, SSPA. Michael Orych, FLOWTECH International and Lars Larsson, Chalmers University of Technology. The paper and the detailed results are available at www.rina.org.uk/IJSCT

Illustrations

Four different keels was evaluated. Three bulb keels and one standard fin keel as reference. Illustration: SSPA

The paper; “Comparison of Modern Keel Types for Sailing Yachts” was published in RINA, Vol 159, Part B2, International Journal of Small Craft Technology.