From May - June 1990 issue of Multihulls Magazine

TRIFOILER By Greg Ketterman

Sheet in slowly and the boat begins to accelerate heeling less than two degrees, its getting lighter and you can hear and feel the waves hitting the bottom of the hull. Suddenly the main hull and the leeward ama are free of the water and the boat accelerates to 20 knots as the sails are once again luffing. The apparent wind just clocked forward 50 degrees. You figure the wind is gusting, but in reality you are creating your own apparent wind. You sheet the sails in and suddenly the gentle 15 knot true wind turns into 35 knots of apparent wind. The apparent wind is so strong that the mist from the windward sensor is blinding. Your goggles are absolutely necessary.
Within seconds you are across the bay and you must turn. Making a quick check to make sure there are no windsurfers, jetskis or buoys in the way, you are grateful for the perfect vision ahead. Inspite of every sailors worst fear regarding bearing away in a strong wind, you press gently with your big toe on the weather side of the steering pedals and the boat bears off quickly. The sails are immediately loaded and the boat accelerates even faster. Half way through the gibe, the foils are now pushing in the old leeward direction. The centrifugal force presses you against the side of the cockpit. The sails gently gibe over as the apparent wind stayed in your face throughout the gibe.
You are now on your new tack, accelerating toward 30 knots and the boat rolled but a few degrees. Heading TriFoiler up to 60 degrees off true wind, it continues to fly. Pushing gently with your big toe on the leeward side, the boat quickly sails through the eye of the wind on the foils and gains many boat lengths to weather. The sails fill and the craft begins to accelerate on the new tack just before the stern of the hull touches the water.
Now you bear away to about 135 degrees off true wind, effortlessly flying at over 25 knots which produces a VMG (velocity made good) to leeward that will embarrass any beach catamaran.
At high speeds the noise from the wind and the sensors slapping the water is loud, but the sensation of flying a sailboat so fast, smooth and effortlessly just off the wave tops is truly exhilarating. The steering is accurate and responsive, which gives it the ability to tack or gibe at a moments notice. A sailor's fear of heeling or capsizing is so deep rooted that it takes a while to gain confidence, but after a few high speed runs and hard gibes it easier to relax and enjoy the ride.
When the wind is steady between 10 and 15 knots you can sail back and forth without ever coming off the foils between true wind angles of 60 and 135 degrees. You can sail as fast as you dare; however, you must have the courage to sheet in. One can sail so fast that you'll think the boat is going to fly apart, but it does not. The excitement is so intense that it is hard to catch your breath, so you decide to let the sails luff. It is no use however, the boat tears along at over 20 knots with the sails luffing. Finally you head it into the wind so you can catch your breath and you realize that your toes are wrapped around the steering pedal so tight that you have developed a cramp in your foot.
If you have ever sailed an iceboat or landsailor you will think this is a description of that experience, but this is a description of the author's experience sailing TriFoiler.
Anybody who has considered high speed sailing has probably considered the idea of hydrofoils and after a few calculations he would realize that a hydrofoil sailboat should sail between two and three times the speed of the wind.
The questions that beg to be asked are: If the speed potential of a hydrofoil sailboats is so great then why are not hydrofoil sailboats more popular? And why are the existing hydrofoil sailboats so slow? This article will answer these questions and describe the development and features of TriFoiler.
A hydrofoil sailboat is analogous to flying a very unusual airplane not more than 12 inches above a very lumpy surface with the landing gear up. This is analogous because if a hydrofoil sailboat does not stay within approximately a 12 inch vertical dimension there will be dire consequences. For example, if the boat goes too low then the hull hits the water and defeat the purpose of the foils. If the windward foil comes up too high and comes out of the water, then the boat could tip over. If the leeward foil comes up to high, then the foil will ventilate and the boat will crash down. The airplane is unusual because instead of placing the engine pointing straight ahead so that the thrust vector lines up with the drag vector, the engine is 10 feet above the wings and pointed predominantly to the side. This is because the thrust of any sailboat is predominantly to the side at the center of pressure of the sail which is way up above the drag vector of the boat. And instead of a good steady thrust, the engine is spitting and sputtering as if some kid is playing with the throttle. This is because the wind is never steady. Would you want to fly in this plane? This is what a hydrofoil sailboat is like and it illustrates how complicated the design of a hydrofoil sailboat must be.
TRIFOILER FEATURES
TriFoiler is a hydrofoil trimaran with two slightly canted fully battened windsurfer style rigs mounted at each end of the single beam and incidence controlled hydrofoils to lift the hulls free of the water and keep the boat level. The pilot sits in a centrally located cockpit, controls the sails with a single main sheet and steers with his feet. Because of it's unique design, there is no need for elevator control from the cockpit.
SPEED
The TriFoiler has a faster maximum speed than any other sailboat over a wide range of wind conditions. This Includes Dennis Connor's multi million dollar Stars & Stripes catamarans, windsurfers, trimarans and all other hydrofoil sailboats. TriFoiler recently raced at officially sanctioned speed trials in Texas where it was clocked at 25.34 knots average speed over a 500 meter course in 10-12 knots of wind (see Multihulls Jan.-Feb. 1990). Unofficially TriFoiler has sailed at an estimated 38 knots in winds gusting to 30 knots. Simply stated TriFoiler is the first practical sailboat than can routinely sail two times and possibly 2.5 time wind speed.
EFFICIENCY
The efficiency of a sailboat is the ratio of boat speed to the true wind speed and TriFoiler is incredibly efficient. Measuring the efficiency of a sailboat is very difficult, because you need to know boat speed and wind speed at the exact same time. The Lake Buchanan Speed Trials had very good equipment for measuring efficiency and TriFoiler consistently produced efficiency numbers between 2.0 - 2.3.
MANEUVERABILITY
TriFoiler can turn quicker and produce more lateral acceleration than almost any other water vehicle. With just three slender foils in the water, TriFoiler has practically no resistance to yaw in contrast to sailboats that have long slender hulls in the water. With TriFoiler's natural ability to produce lateral resistance from the struts, TriFoiler can produce very large lateral acceleration. Power boats generally do not have the ability to produce lateral force; therefore, they can not produce lateral acceleration.
In most sports (windsurfing, sports cars, skiing, motorcycles, surfing, etc.) turning is a big part of the fun, with sailing it has not been so because, frankly, on most sailboats it is boring and laborious. Typical sailboats nearly stop when they make a turn and sails need to be reset. TriFoiler will bring a whole new aspect to sailing, because it can turn at breathtaking speeds.
SIMPLICITY OF OPERATION
TriFoiler is simpler to operate than any other small sailboat, because the pilot does not need to worry about keeping the boat level or capsizing. Typically the pilot of a sailboat needs to the work the sail, the rudder and move his weight from side to side to keep the boat from heeling. With TriFoiler the hydrofoils automatically keep the boat level. Also the boat is inherently more stable because the center of effort is lower and the boat is wider. Hence the pilot of TriFoiler merely relaxes in a bucket seat, steers with his feet and adjusts the sail with a single line with his hands.
SAFETY
Even though TriFoiler will be traveling at speeds much faster than typical sailboats, it is safer than other sailboats for several reasons;
1) Typically the pilot of small performance sailboat needs to hang their weight over the side from a trapeze. Also it is not uncommon for these boats to come to stop very quickly and the people on the trapeze go swinging through the air out of control.
2) TriFoiler has no boom any where near the passenger area (Thus giving one "Peace of Mind"). All sailors are too familiar with the hazards of a fast swinging boom.
3) Capsizing is highly unlikely in TriFoiler in contrast to typical small boats.
4) Typically the passengers of small sailboats need to move all over the boat for various reasons and the boats have many hard sharp objects on them. Sudden movements can result in many scratches and bruises. On TriFoiler the passengers remain seated in the safe confines of the cockpit.
COMFORT
For a very long time it has been the desire of many designers to come up with a high performance boat where the passengers can sit in a single seat looking forward and keep dry and comfortable. In the past sailors had to choose between dry comfort or high performance. With TriFoiler a sailor can have dry warm comfort and high performance.
TRIFOILER DEVELOPMENT
The TriFoiler project has really been a life long ambition since I have experimented with models my whole life, but the real beginning happened with the success of the 1/4 scale remote control model shown in figure 1 which was built in 1980 while going to Cal Poly Pomona. I have always felt that the real achievement has been the development of a good working model. The challenge of making a model hydrofoil sailboat work is much more difficult than a full size boat. A model is more difficult because the major challenge is getting the controls to work and it is difficult to know what is actually happening on the model. The fact that the model does work is a tribute to the practicality and stability of the basic design concept.
The model displayed high performance and good stability in a variety of conditions including winds gusting to 20 knots. It was faster than a Hobie 16 with an estimated top speed over 20 mph. The model was capable of fast gibes and was in general very maneuverable.
The project got put on the back shelf as I pursued an engineering career in aerospace. Fortunately the aerospace business did not agree with me and I decided it was time to build the full size prototype. By the end of 1987 and after nine months of development the first prototype, shown in figure 2, was completed and proved to be practical, fast and fun.
Participation in the design of the Stars & Stripes catamarans and other business interests diverted our attention away from TriFoiler for about a year and half. During that time we developed the design of the second and latest prototype as shown on the cover and figure 3. Design and construction was completed in just 10 short weeks just time for the speed trial in Lake Buchanan, TX in Nov. 1989. Again the objective was primarily speed, but also I wanted the boat to be more practical. The bi plane rig has many advantages including better sail control, lower center of effort, and it allows shorter main hull with a centrally located cockpit. The new beam is wider and more aerodynamic.
Extensive use of CAD (Computer Aided Design) greatly improved the boat by facilitating the design and construction. CAD application included performance modeling using our own VPP (velocity prediction program), computer drafting, computer lofting and Finite Elements Analysis. Also many spread sheets are used to keep track of weight, cost and miscellaneous stress calculations. Construction was made easier by using the plotter with a lofting and drafting program to plot full size drawings and use the drawing as a template to cut out the part.
The main hull is glass foam sandwich and the amas are basic surfboard construction. The main beam and compression strut are uni directional carbon fiber over foam and the foils are unidirectional carbon fiber over wood. Anchor Reinforcements supplied all of the unidirectional carbon fiber. The boat is very light primarily because the structural advantages of the design. Some small parts of the boat are very highly stressed, but compared to typical beach catamarans there are not as many large loads in large parts; therefore, it is considerably easier to make the boat relatively light. Also it is not necessary to provide as much buoyancy to prevent pitch poling since the foils do the lifting when the wind is blowing; therefore, the boat is smaller and lighter.
HYDROFOIL SAILBOATS IN GENERAL
Hydrofoil boats can be categorized into two categories; 1) Incidence controlled hydrofoils and 2) surface piercing hydrofoils. The difference lies in the way the boat maintains the proper altitude above the water surface. A surface piercing hydrofoil boat maintains proper height by varying the amount of foil submerged. The boat raises up as the speed increases and reduces the amount of foil submerged and therefore the lift. The boat finds equilibrium at the proper altitude. An incidence controlled hydrofoil sailboat has a mechanism that controls the angle of attack of the foil to maintain the proper altitude. It is generally believed that surface piercing is simpler, but incidence control is more efficient. In reality, it is the method that works with fewer problems that is simpler.
From the beginning it was felt that incidence control was better suited for a sailboat even though most of the existing hydrofoil sailboats were of the surface piercing type. There are many advantages of the incidence controlled foils; however, the most important is what I call the DLA (dynamic leveling affect). This is the increase in righting moment or stability due to the ability of the windward foil to pull down. The DLA has little affect on the low wind performance, but it essentially makes the top speed of the boat limited to the strength of the boat. Conventional boats with a finite amount of righting moment can only extract so much power from the wind, but with the DLA, the righting moment is virtually unlimited.
Intuitively many people think that the added drag of the windward foil plus the increased induced drag of the leeward foil would offset the gain in righting moment, but calculations show and practice proves otherwise. The dynamic leveling affect not only produces a dramatic increase in top speed, but is also responsible for all the other key features that this stability provides.
The other major advantage of the incidence controlled foils is they are less affected by the waves and other surface affects. Drag and losses associated with the surface are the major reason incidence controlled foils are more efficient.
All hydrofoil sailboats have problems with ventilation; however, surface piercing foils have larger problems, because the foils are piercing the surface at a smaller dihedral angle which makes it easier to ventilate.
LATEST DEVELOPMENTS
We have been working for over a year with a large RV product manufacture and I hope that a consumer version will be available soon.
Very shortly I will be in direct competition with Russell Long for the world speed records. Russell is a very successful professional sailor (12 meters & Ultimate 30's) and has bought a TriFoiler for the purpose of assaulting world speed records under sail. We welcome the competition and I am excited to see the sport of speed sailing gaining popularity.
Officially sanctioned speed trials are going to be organized during the summer of 1990 somewhere on the west coast. If the Gods favor us with good winds, we hope to set new speed records.
CONCLUSION
TriFoiler uses a new hydrofoil concept (patent pending) to create a boat with a number of unique features. With these new standards for speed, efficiency, maneuverability, comfort, simplicity of operation, and safety, the possibilities are many.
Just a few of the possibilities would be the introduction of the first production hydrofoil, increased interest in speed sailing and a new professional sailing circuit for hydrofoils.
I imagine a race similar to the slalom races for windsurfers would be very successful as a professional circuit. This circuit would have many advantages over existing circuits. For example, a slalom race would take advantage of the boats ability to gibe and would be very exciting for the participants and spectators. Racing around a pair of buoys in a figure eight would be simpler to understand on TV. Viewing from a spectator area would be much easier. Campaigning a TriFoiler would be much cheaper than an Ultimate 30 or Formula 40.
ABOUT THE AUTHOR
Greg Ketterman is a 31 year old mechanical engineer and naval architect from Long Beach, CA. He graduated from Cal Poly Pomona with Bachelor of Science Degree in Mechanical Engineering. Greg grew up sailing and racing Hobie Cats and experimenting with model multihulls and hydrofoils. He became an avid windsurfer in 1982 and lived on Mauii for 10 weeks to get his fill of windsurfing. He helped with the design of the Stars & Stripes catamarans and helped Gino Morrelli with the design of the Morrelli Formula 40's. He has designs for human powered hydrofoils and other sailboats using this hydrofoil concept including course racers and an asymmetric (starboard tack only) hydrofoil boat designed strictly for speed.