Rudders - We all use them, and yet how much do we know about them? With that in mind, we had a cyber sit down with well known Bravura Yachts President Leif Beiley, to address the topic of the rudder. We learned a lot in the process - we hope you do to!

Windchaser Yachts (WCY) - "Leif, the subject of rudders...as racers we all have them, we all need them, and we all use them...on the topic of rudder design, what are main factors that go into making a rudder what it is?"

Leif Beiley - "The main function of the rudder is obviously to control the direction a boat moves. However, in a modern racing sailboat, the rudder also helps generate lift to weather while minimizing drag. Years ago, rudders were flat slabs of wood that pivoted on a stock and altered the course of a boat by resistance. Turn the rudder to starboard and drag increased on the starboard side and the boat slewed around in that direction.

As designers began to understand the that foil shapes actually generate lift we started to build rudders with foil shapes that generated side forces that were greater than the side forces generated by flat slabs. These days, rudders and keels are essentially wings that fly through the water a lot like airplane wings fly through the air. The aerodynamic difference between a rudder and an airplane wing is that airplane wings are horizontal and only have to generate lift in one direction; up, so they are asymmetrical foils. A rudder is vertical and has to generate lift in both directions so it is a symmetrical foil."

WCY - "Rudders design, has from my observations, evolved into shapes that have more depth, but less chord length -is this a response to the newer hulls they are "driving" or just increased knowledge regarding foil effeciency?"

Beiley - "The shape, or plane form of a rudder has evolved because of two factors. First, we continuously learn more about what shapes are most efficient. Second, we continuously apply advances in materials and processes to the design of rudders. We know that a rudder of higher aspect ratio, that is, more depth relative to a given chord length, is more efficient. By that we mean it has a higher lift/drag ratio. Without getting too technical, higher L/D ratios mean that a rudder can be smaller, with the same turning power as an older rudder, or it can be the same size but generate more lift. High aspect rudders generate more force so they have to be able to withstand the increased loads on the blade itself, the stock, bearings and control system as well. The use of high strength composites makes high powered rudders possible."

WCY - "Here is a question I have always wanted to ask - if you were to do a rudder re-design on a long skinny boat like the J/27 versus a wider more powerful hull shape like the Pocket Rocket 22 what would be some of the rudder design differences?"

Beiley - "There are many factors that influence the design of a rudder for a given boat. Basically a boat’s overall speed potential is a major factor. You wouldn’t spend the money and energy on an ultra high tech rudder for, say, a Catalina 30 because that boat isn’t going to go very fast anyway. But for the boats you mentioned, both could benefit from thinner, lighter rudders. The J/27 has more speed potential so it could handle a slightly thinner rudder. The 27’s old rudder is square on the bottom and a new design would have a more rounded leading edge at the bottom which reduces the size of the vortex that is created as the water swirls off the tip. The Pocket Rocket has considerably lower speed potential so the planform shape isn’t as critical, and induced drag, such as tip vortices is less of a factor than parasitic drag. Parasitic drag is the result of factors such as frontal area, surface friction and wetted surface. Induced drag is created by such things as tip vortices and foil shape."

WCY - "On the same note, what is the relationship between inboard vs. outboard rudders - As a designer what is your preference and why?"

Beiley - "Outboard rudders are simpler and easier to build. They can be made to kick up for shoal water and trailering, and they are easy to keep free of kelp. However, they are inherently less efficient because they don’t have an “endplate” at the top, and they pierce the surface of the water too. The endplate effect helps keep the water flowing straight aft, which helps prevent the rudder from cavitating, thus losing its ability to generate side force. So, for the most part, an inboard rudder is a more efficient foil. This is why you very seldom see outboard rudders on big boats, including real big catamarans like Playstation. One exception to this generality is the big singlehanded racers. If you’re the only guy on the boat, you want to be able to clear kelp off the rudder without hanging your body over the side while you’re reaching along at fifteen knots 50 miles from the coast."

WCY - "When talking about inboard rudders, suppose you were to design and build a new rudder for an older design, say a San Jaun 24 - would you expect a substantial performance difference on a such a hull shape?"

Beiley - "Well, it depends on what you consider a significant difference in performance. If you built a lighter, deeper and more efficient rudder for your San Juan 24 and then raced it against a fleet of stock 24’s you would notice your trophy shelf filling up a lot faster than before. Of course your boat may not be class legal with a high tech rudder, either. But I would say if you made no other changes you could expect a 6 to 12 second per mile improvement. On a twenty mile reach you would get there two to four minutes sooner than you would with the old rudder. That’s not a big difference, unless you’re racing."

WCY - "Many boats sailing manners are described by the "feel" they produce - can you describe some of the rudder design factors that manipulate the "feel" of the boat?"

Beiley - "The feel of helm is very dependent on the rudder. But it’s also dependent on how much weather helm or lee helm the boat generates. This is referred to as the “balance” of a boat. Boats with a lot of weather helm require a lot of side force from the rudder to stay on course. You’ve seen boats with a lot of weather helm: The helmsman is constantly tugging on the tiller, and the boat tends to round up in a puff. Boats that are well balanced require less side force from the rudder and so are easier to steer. Weather helm is determined by comparing the longitudinal center of lateral resistance of the hull with the location of the center of effort in the rig. In my own designs I try to balance a boat so that upwind it carries about three to five degrees of rudder angle so the leeward side of the rudder is roughly parallel with the centerline of the boat. This allows the rudder to generate maximum lift with minimum drag. If the boat is configured this way I think you get the most benefit from the keel and the rudder acting together to lift the boat to weather. And it results in the best “feel” in the helm.

The amount of balance in the rudder is important to the helmsman because if it has no balance, the helmsperson must use his arm strength to overcome all of the turning moment generated by the boat’s weather helm. If the rudder has too much balance, the helm will always feel light and mushy. Rudders with about 10 percent of the area of the blade forward of the rudder stock usually have about the right amount of balance."

WCY - "Construction - Bravura Yachts is doing a fair number of custom rudders these days - how is a modern day rudder built and with what type of materials?"

Beiley - "For a custom rudder, the first thing I do is analyze the boat and its existing rudder to determine what the potential is for improving its performance as well as to determine what changes we have to make to the boat itself to accommodate the new rudder. The next step is to design the rudder blade, solve for the loads we can expect the rudder stock and steering system to see, and design the stock. We build most of our own rudder stocks out of carbon fiber and epoxy but occasionally we have them built for us out of stainless steel or titanium, depending on the situation. For the blade I first design its planform, basically the side view, then design or select a foil section for it.

To get the blade and stock together we laminate structural foam such as CoreCell around the rudder stock, then fair it down to the correct foil shape and planform using computer generated templates. After the shaping is finished we laminate the outer skin on. This is usually carbon/epoxy composite, vacuum bagged into place. After all of the laminating is completed, the rudder is post-cured in an oven at about 130 degrees F. When it has come out of the post-cure cycle it is ready for final fairing, fitting of bearings, and then paint."

WCY - "Price - Let's say a Santa Cruz 27 owner approached Bravura Yachts to design and build a new rudder - what would they expect to pay and what would they get in return?"

Beiley - "Well, we probably wouldn’t do a custom rudder for a Santa Cruz 27 unless the owner was certain that he was not interested in racing the boat as a one-design. But there are lots of boats in that size range that can benefit greatly from rudder upgrades. Since we have several molds for high performance rudders the first thing I do is check to see if one of them would be a good fit. Often we can modify a rudder from one of our molds. If that’s possible it saves the client a substantial chunk of money.

The cost of a carbon epoxy rudder with a carbon fiber rudder stock from one of our molds ranges from around $2,000.00 to $5,000.00 depending on size and extent of modifications, if necessary. If we have to build it as a custom one-off rudder the prices start at around $3,000.00. Our carbon rudders are perfectly faired and ready for bottom paint when we ship them. They usually weigh 50 or 60 percent less than a standard rudder, and they are generally deeper, thinner and of a shape that is geared for maximum performance.

For rudders on most production boats, cost and ease of manufacturing is a high priority, so production builders don’t use carbon and epoxy or fair them to the standards we use. A general rule of thumb is that a state of the art rudder will increase a boat’s upwind speed six to 12 seconds per mile, a bit more on downwind legs."

WCY - "Based on the above, how do you actually calculate roughly, the profile, dimensions, and laminate schedule for such a rudder?"

Beiley - "Both the plan form and the foil sections of our rudders are the result of the considerable research and development we’ve done for my own designs and for other custom racers. The rudder stocks are engineered using the American Bureau of Shipping (ABS) Rules for Building and Classing Offshore Yachts as a starting point. Laminate schedules are derived from our in-house engineering of the loads. Our empirical data indicates that a highly efficient rudder can have ten to fifteen percent less surface area than a typical old-style rudder. This is usually manifested in shorter chord lengths, thinner foils and, as I mentioned, deeper blades."

WCY - "The future - where do you see rudders going over the next five years? Any major changes ? Will profile be more of an issue or is it more technology and construction that will be pushed?."

Beiley - "Developments in basic rudder shapes are continuing, but I think they have reached a state of refinement in which the changes we’ll see in the near future will be incremental and evolutionary rather than radical. However, one area that shows promise is the use of wings and endplates on rudders. You maybe surprised by some of the next generation of America’s Cup boats. I can’t say much more on that subject, except to look for some innovation there. Of course materials and processes will continue to advance. As the technology filters down to them, I would look for more production builders to incorporate carbon/epoxy technology in their rudders. Here in our shop we continue to improve our methods and materials as well as our designs. With each new rudder we add a little to our database and learn a bit more about what works and what doesn’t. This kind of development is a lot of fun to do, and helps us stay a step or two ahead of the competition."

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