Practical Aspects of Canting Keel Design, Construction and Analysis

Abstract

In the last decade canting keels have moved from the exotic to the mainstream in offshore racing yacht design. Now classes from Minis to Maxis are designed with canting keels, but several recent high profile failures in the Vendee Globe and Sydney Hobart have brought designers back to the drawing board to have a closer look at the design and construction methods involved for both the keel fin and the actuation system. Although rules are now beginning to appear for stability criteria and safety in the event of actuation failure, there are not as yet any general structural guidelines beyond the ABS Guide for Offshore Racing Yachts. Aimed at more conventional yachts they can never hope to take into account the complicated loadings on canting keels. Estimates of hydrodynamic loads, slamming loads, grounding loads and loads from the ever increasing danger of hitting unidentified floating objects must be made. Then tools such as FEA are invaluable in the analysis of a structures response. Choices of material and construction are based on the type of yacht and racing it will be required to do as well as restrictions in some class rules such as the Volvo Open 70. Optimisation of sailing characteristics, weight, safety and operation are all taken into account. Once built and fitted, the work is not over as keels are routinely checked for structural integrity before and after major events even before their estimated fatigue mileage is complete. Owen Clarke Design has been associated with canting keel design for many years, during which time there has inevitably been an evolution in techniques and many learning experiences. The aim of this work is to pull together our experience in design, construction and analysis into a reference that others may benefit from and add to, in order to improve safety and reliability of canting keel design.