Rudder Design "We have just finished the Cape2Rio race and had some very hard days running. We are all in agreement that without your rudder we would not have won this event!" - Owner, Carkeek 47, Black Pearl. Owen Clarke Design are specialists in the design, analysis and engineering of sailing racing and cruising yacht rudders and foils. We extend this service to owners and sailboat designers, both for new boat, as well as troubleshooting and repair during the refit of existing yachts. Our smallest rudders to date have been on a 6.5m mini Transat and the largest on a 35m twin rudder superyacht project for which we were contracted as consultants. OC act as consultant engineers, as well as experts in trouble shooting steering control and balance issues, of which many we find we are able to remedy without complete blade or rudder replacement. All our rudders and foils are designed using 3D software with sections customised for each project from our extensive library of CFD developed shapes. Output to specialist manufacturers and boatbuilders is in the form of IGES files. OC can help reduce construction costs by adapting our deliverables to suit their manufacturing process; be that hand or CNC mould making, steel or carbon stock, male formers or female moulds for composite blade and/or stock. For owners that have had problems with their current rudders that can be resolved with a new blade, we are in some cases able to check their current stock complies with ISO requirements, review bearing loads and then redesign a new blade around their existing stock. In addition to spade rudders, OC have experience in transom hung, lifting, kick up and skeg/semi balanced rudder design. Engineering is undertaken in-house for composite or metal stocks to whichever relevant standard, ABS, ISO and where required in conjunction with certification organisations, typically, but not limited to GL and IMCI. Deliverables are in the form of 2D CAD files, material lists and when required manufacturing guidelines. For metal rudder posts we advise on and adapt our engineering to locally available grades of stainless steel and aluminium. For composite carbon rudders OC adapt the characteristics of the post layup to the manufacturing processes available: manual impregnation, pre-preg, vacuum or auto-clave consolidated. When required we are also able to apply our accumulated knowledge in failure cases where expert consultancy is required to resolve disagreements between third parties, insurers, etc. OC are also one of the world’s most experienced designers of high speed/high Froude number rudders for multihulls and monohulls. Our first racing trimaran was launched in 1988 and our first twin rudder monohull in 1993. We currently have over forty different two rudder monohull designs on the water, as well as having towing tank tested almost twenty different twin rudder hull models and run thousands of CFD solutions for this appendage type. Consequently, OC apply this knowledge both on our own new designs but also make it available to other owners and designers. Our experience, both theory and practical gives us an almost unique insight into geometry and balance problems in this complex and often mis-understood area of yacht design, allowing us to either avoid or troubleshoot the mistakes of others. This image is an example of a common phenomenon we have seen and been approached to solve in recent years. This is the aft section of a racing yacht, scanned in the boatyard with a laser and then transformed into a hull file. The yacht was designed with twin rudders with stocks exiting the hull at the green circle X. The horizontal plane cutting through the new rudder is the at rest waterline. The yacht exhibited control issues including broaching coming out of gybes and when tight reaching. In this grand prix sailboat, all four of the most commons design faults we come across were present in the same case. OC’s recommendation was to revert to a single rudder for which the hull was clearly most suited. This was deemed to be unacceptable by the owner and so we reverted to a compromise solution illustrated here, with two new rudders. |
