The primary goal of sail optimization is to increase the lift (for a good drive force component) and reduce the drag (stability must be maintained during the process). Sail optimization is a repetitive job. This is because, like wings, the drive force of the sail in up-wind sailing depends on the apparent wind vector (direction and magnitude), the planform (area & aspect ratio), the camber (flat or curved cross sections), the gap between the fore and main sails, the mast and other parameters (such as height above the deck, hull shape, etc.).
Stallion 3D Simulation of flat thin sails. The graphs shows pressure.
A good design does not simply mean infinite aspect ratio to reduce tip vortices (tip vortices increase drag as seen in above picture). The heeling moment will be too big (unless, of course, you have this installed on your boat). Large camber or deeper sails can increase the drive force, however, stability and drag from supporting underwater devices (keel and rudder) can erode this advantage. To obtain the optimal (or best we can do at the moment) specifications for a particular sail, we must test our design iterations against a number of possible sailing conditions.
Stallion 3D Simulation of cambered thin sails.
Stallion 3D Simulation of cambered thin sails with a larger angle between jib and main sail.
No sail optimization study is complete without the consideration of the underwater systems (keel, rudders and other appendages). Like sails, keels and rudders are wings and also behave as wings. The goal to provide stability and lateral resistance can result in drag (induced and profile). Also, an efficient keel for up-wind sailing can be terrible otherwise. In short, sail and keel/rudder analysis are coupled and equal partners in sailboat optimization.
Stallion 3D simulation of a keel and bulb.
In the area of aerodynamics conceptual design, a lot of nautical mileage can be quickly covered with a tool that has a built-in set of realistic physical assumptions, automatic grid generation and cost effective and readily available computing platform. Stallion 3D can be deployed on an ordinary Windows PC, run in multiple directories to take advantage of multi-core processing and efficiently and accurately analyze the most difficult models.
Graph shows surface speed in m/s.
More information can be found at http://www.hanleyinnovations.com/stallion3d.html. The cost of a 3-months lease of Stallion 3D is $895.
Thanks for reading.
Do not hesitate to email or call me at (352) 240-3658 if you have any questions.