The mainsail is a wing sail lengthwise divided into two parts which can be set at various angles. Reproduced with permission from Rick Tomlinson. The main lift-generating hydrofoil is working on the port side while it is in a retracted position on the starboard side.
The lift-generating foils at the end of the rudders incidentally serve also as winglets for the rudders themselves, diminishing their induced drag. The contact with water is established only via three hydrodynamic foils. Port and in front on the leeward side there is a lift-generating surface, placed where a classical centerboard would be. Its function is to lift the hull out of the water and to counteract the sail side force. The two rudders carry additional horizontal foils at their ends. Their attack angles are set for positive lift on the leeward side and for negative lift on the windward side.
The reason is that, no hull being in the water, both the heeling and the forward tilting pitching moments of the sail the centre of aerodynamic force is several meters above the water plane have to be compensated for. In a classical sailboat, the heeling and pitching moments can be met by the buoyancy of the hull.
Here everything has to be done by the forces generated by the hydrofoils. Figure 14 gives a closer look on the forward foils. On the windward side it is drawn up, and the lift-generating horizontal, slightly oblique part is seen. On the leeward side both the side force generating part and the lift-generating part of which you can see just the tip , joined by a curved intermediate piece, are effective in the water.
They can be lifted, canted tilted sideways along a lengthwise axis and rotated about a vertical axis in order to change the attack angle. We can plot aerodynamic lift against drag and thus obtain a polar diagram of total aerodynamic force. A typical example is shown in figure Making use of equations 8 and 14 we can also plot directly the lift coefficient c L against the drag coefficient c D , which is then called a Lilienthal diagram.
Sail polar diagram and boat sailing close-hauled. Tangent normal to the course sailed dashed line onto the polar diagram will give largest sail driving force F A. Lift increases steeply with attack angle, until after reaching a maximum flow separates behind the nose. At very large attack angles, the aerodynamic profile delivers its force mainly in the form of drag instead of lift.
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Although this is relevant for conventional yachts running before the wind, high-speed sailing always exploits the regime of attack angles left of the maximum. The smallest possible glide angle with a given profile is obtained by drawing a tangent to the curve from the origin.
As there is always some drag, the polar diagram does not contain the origin. The horizontal offset is increased further by additional resistance by mast, shrouds, spreaders, and the hull 'parasitic' resistance. With respect to a sailing boat, the x -axis drag of this diagram has to be oriented parallel to the apparent wind direction, We can graphically obtain the largest possible driving force component F A by laying a tangent to the polar curve normal to the direction of course.
Due to the relation. This is, in fact, what the sailor actually chooses by easing or hardening the sheet. Assuming this to be correctly done and all other rigging parameters to be optimally tuned, we can draw a polar curve for boat velocity which shows a characteristic heart shape figure Speed polar diagram for a conventional keel yacht 12 mR. True wind speeds 7, 12, 20 knots.
Common tangents reveal the most effective tacks and the effective upwind velocity VMG. For gybing downwind, the method is analogous. In this diagram, true wind comes from above negative y direction. In all sectors where the polar diagram is convex, the best course direction is that indicated by the diagram.
In all sectors where the diagram is concave, the fastest courses are determined by common tangents. Most notably this is the case for beating to windward. The best tacks for upwind sailing are given by joining the origin to the osculation points of the tangent common to the symmetric starboard and port parts of the curve.
Thus we obtain the largest velocity component in the windward direction the y component of the velocity vector , usually called velocity made good VMG. Mind that this does generally not correspond to the smallest possible angle a boat can sail to the true wind. Especially with high-speed yachts, a comparatively larger angle to the true wind direction is often favoured. This is very pronounced after a tacking maneuver when it is imperative to gain speed quickly in order to reach sufficient side force. Not only upwind, but also downwind high-speed boats show a concave velocity diagram.
Here the same principle applies: the best course directions are obtained by laying common tangents. Therefore these boats gybe downwind in successive laps. Figure 17 shows speed polar diagrams for fast boats, an 18 ft skiff and a Tornado catamaran. Grey areas show the concave regions for the 18 ft skiff. We already talked about beating upwind and gybing downwind sectors I and III. The polar diagram of the 18 footer has a pronounced 'nose' for broad reaches as a very high speed can be reached on this point of sailing with a gennaker sail.
In sector II this means that e. Note that the downwind effective velocity VMG is greater than the true wind speed. Speed polar diagrams for an 18 ft skiff and a Tornado catamaran. Grey: Concave sectors details: see text. At present we experience a sailing speed explosion on water The m speed record of reads Although this achievement required a very special setting the runs were made in a narrow canal , speeds in excess of 40 knots have been reached at the recent America's Cup regatta with foiling catamarans. True wind speed, in contrast to a long-held popular belief, is not to a limiting barrier to boat speed, which is borne out by present-day sailing performance: you can sail upwind with an effective VMG several times the true wind speed, and you can out-sail downwind a balloon drifting with the wind.
Although the basic physics of high-speed sailing has been known for at least a century, this evolution could only take place as extremely light-weight and strong materials have become available, mostly compounds of epoxy resin and carbon or aramid fibres. At the same time computational fluid dynamics [ 13 ] and wind tunnel tests have greatly refined hydro-aerodynamic know-how. It is an ironic twist of history that nowadays when sailing ships as freight transporters are a thing of the past, sailing technique in the realm of sports has been improved to an unprecedented degree.
If we want to sail at high speed, we must reduce aerodynamic and hydrodynamic glide angles, which is equivalent to achieving high lift to drag ratios. Provided one can build efficient wing sails and underwater profiles, the main problem remaining is wave drag. A classical sailing yacht displaces as much water as it weighs and builds up considerable wave mountains, reaching a barrier to further acceleration at hull speed. In a first step, this barrier was overcome when light-weight boats were constructed that were able to plane easily.
Thus they could enter a state where part of their weight was carried by hydrodynamic lift and the wave drag was considerably reduced. The second step is foiling : the whole weight of the boat is carried by hydrodynamic lift. It goes without saying that a boat sailing on two to three 'stilts' is difficult to stabilise and control. Even in this respect, great progress is being made, and more user-friendly foiling boats are beginning to enter the market [ 14 ]. The edition of the America's Cup, the oldest and most renowned sailing competition, brought with it a paradigm change in speed and media coverage.
For the first time foiling catamarans were employed, and the unfolding drama of the race was brought to the TV spectator in hitherto unseen detail, showing current speeds, expected positions at crossings, VMG, wind shifts, positions with respect to the mark etc. This was partly done also in earlier editions of the America's cup. Thus sailing became a spectator sport.
What is more, the improvements in speed, strength to weight ratio, and sophisticated aerodynamics yield many spin-offs for the common yachtsman, and we can confidently expect that many of the features which almost seem out of science fiction today will become commonplace. Further reading on sailing physics: apart from the author's book [ 2 ], which is available in German only, the works by Larsson, Eliasson and Orych [ 11 ] Anderson [ 15 ] rather concise , Garrett [ 16 ], Kimball [ 17 ] and Fossati [ 18 ] are recommended. We designate vector entities by the term 'velocity' and speak of 'speed' if absolute values are meant.
For simplicity, for the time being we understand all forces to be parallel to the surface of the water. According to a well-known theorem of classical mechanics, any distribution of forces working on a rigid body can be replaced by one couple and a resultant force. Streamlines are the field lines of the velocity field in fluid flow. The tangent vector to a streamline is always parallel to the instantaneous local velocity vector. The following explanation is accepted knowledge and can be found for instance in [ 3 ].
The reasoning presented here can be found in more detail in textbooks on hydrodynamics, e. A derivation can be found in [ 10 ]. Actual hull speed, defined as the speed at which wave drag increases sharply, however depends on the shape of the hull, so that some boats may be driven well beyond the speed given by equation Google Scholar.
Author e-mails. Introduction Driving a ship by the force of the wind is an ancient technique harking back to the very beginnings of human civilisation. Zoom In Zoom Out Reset image size. The second popular explanation correctly invokes Bernoulli's theorem:. Apparent wind: Wind as perceived in the reference frame of the moving boat. Beam reach: Point of sailing with the true wind at right angle to the course. Beat to beat : A boat is beating if it moves in a zigzag fashion towards a target which cannot be reached directly or which can be reached faster this way.
Also: one of the zigzag laps. Bow: The forward end of a boat. Centerboard: Like the keel, a vertical plate in the centerline of the boat put into the water in order to generate hydrodynamic side force and thus prevent excessive leeway. Close-hauled: A boat is close-hauled if it sails with a small angle to the wind so that the largest velocity component to windward can be obtained. Ease to ease : To ease a sheet means to release part of it in the direction of the pull, so that the attack angle of the sail will be reduced.
Gennaker Large downwind sail hybrid of a spinnaker and a genoa mostly set on a bowsprit pole extending from the bow. Gybe or jibe : Maneuver to change the side from which the boat receives the wind by turning the stern through the wind. Harden to harden : To harden a sheet means to pull it tighter so that the attack angle of the sail will be increased.
Heel: Sideways tilt of a boat. Also: to heel over : to tilt sideways. Keel: Besides being a construction element in a boat's hull also a vertical extension of the hull, mostly in the form of a hydrofoil fin keel , with ballast attached to its lower end. Leeway: A sideways drifting motion of a boat due to the aerodynamic side force. Pitch to pitch : Movement of a boat about a transverse axis, for instance when dipping the bow.
Plane to plane : A boat is planing if it moves at a speed greater than hull speed, receiving hydrodynamic lift so that it displaces less water than it weighs. Rig: Sails and the complete construction supporting them like mast, boom, standing rigging. Rudder: Immersed blade by which a boat is steered. Running: Sailing with the wind from abaft: before the wind.
Sheet: A rope serving to control sail as to its position relative to the wind direction. In the terminus 'vortex sheet' the word 'sheet' is however used in its commonly known meaning, i. Spinnaker: A balloon-like sail set on reaches and running. Stern: The rear part of a boat. Tack to tack : Maneuver to change the side from which the boat receives the wind by turning the bow through the wind.
Also: the laps of course between tacking maneuvers. True wind: Wind as perceived in a reference frame where the water is at rest. Deep water means that water depth markedly exceeds the wavelength. Babinsky H How do wings work? Prandtl L Gesammelte Abhandlungen 3 Bde. Berlin: Springer in German Google Scholar.
Cross R Effects of turbulence on the drag force of a golf ball Eur. A boat is beating if it moves in a zigzag fashion towards a target which cannot be reached directly or which can be reached faster this way. Like the keel, a vertical plate in the centerline of the boat put into the water in order to generate hydrodynamic side force and thus prevent excessive leeway.
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A boat is close-hauled if it sails with a small angle to the wind so that the largest velocity component to windward can be obtained. To ease a sheet means to release part of it in the direction of the pull, so that the attack angle of the sail will be reduced. Large downwind sail hybrid of a spinnaker and a genoa mostly set on a bowsprit pole extending from the bow.
Maneuver to change the side from which the boat receives the wind by turning the stern through the wind. To harden a sheet means to pull it tighter so that the attack angle of the sail will be increased. Besides being a construction element in a boat's hull also a vertical extension of the hull, mostly in the form of a hydrofoil fin keel , with ballast attached to its lower end.
Movement of a boat about a transverse axis, for instance when dipping the bow.
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A boat is planing if it moves at a speed greater than hull speed, receiving hydrodynamic lift so that it displaces less water than it weighs. Joelle was great — she made me feel like I could do it and she took more time with me to go over things when I needed it. She instilled great confidence and I felt really comfortable with her.
I am so glad that she was our teacher, thanks Joelle! Tucker wrote: Had so much fun! Never thought I could enjoy a vacation this much but I was wrong! Jane wrote: We came to class with no prior sailing experience and left with 3 certifications, a new vocabulary and a new friend. What a wonderful experience for our family of 3 to learn and cruise together! I highly recommend Fast Track to Bareboat Cruising! Tim wrote: Excellent experience. This week has created an unforgettable memory for me and my family.
This experience has changed my life. Cheyenne was excellent. Very patient, we were completely new to sailing and in a week we felt very comfortable with all aspects. Down in the BVI right now and we just finished our weekend course and are now, on our foot catamaran and getting ready to head out tomorrow for a week of sailing. So far, it has been absolutely amazing and has exceeded everything I could have hoped for. My wife and I had an unbelievable experience learning to sail with Offshore.
We both had zero prior experience.
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Both of our instructors had decades of sailing and instructing knowledge. They imparted both competence and confidence on the water. We look forward to chartering a catamaran in the Mediterranean next year and ultimately living aboard our own boat someday. We would both high recommend Offshore to anyone. I understand that there is still a lot to learn, but I will be confident enough to start chartering a boat now.
Cheyenne was a pleasure to work with, clam and confident and very knowledgeable. I was very apprehensive coming into the course. The knowledge of the instructors, materials and practical experience took away my anxiety and made me feel like a sailor! Both instructors were excellent! Very respectful, encouraging and excellent knowledge. Excellent all around! The combination of the South Seas Island resort activities that kept my children busy and happy while my wife and I were able to focus on the class.
Patrick was a great instructor. He had just the right balance of knowledge, patience and firm corrections when needed. He gave me a great deal of confidence and I. My overall experience was excellent. Cheyenne was incredibly patient. The boat was well provisioned and I had so much fun. I was nervous about leaving and coming back to the dock, but I am much more comfortable now.
Cheyenne is a fantastic instructor. He is incredibly patient and knowledgeable. He provided us with all of the information we needed. It is clear he has a passion for sailing and enjoys passing his experience and knowledge. Great experience learning to sail and basic cruising. It was fun. Second course with Offshore Sailing School and both experiences have been great, fun with lots of learning. Instructor very courteous and patient. Extremely patient with docking procedures and anchoring. Well done. Combination of books, instruction and practical experience reinforced the skills.
Hunter was beyond fantastic — like having an extremely knowledgeable and patient friend show you how to sail. Extremely levelheaded and cool under pressure, patient and knowledgeable about sailing and the onboard systems. This course was exactly what I expected and wanted; a good refresher on Basic Keelboat. Fast Track to Live aboard Cruising has given me the knowledge and humility to handle my new boat. Our instructor, Hunter Botto, was exceptional! Clear, concise, patient. Thoroughly knowledgeable; practical and theory. Wonderful to spend time with. Enthusiastic and patient.
Made it effortless learning. My wife and I were at different sailing experience levels. We wanted to take the Fast Track to Cruising course together and we were not sure what to expect. We were pleasantly surprised with the entire program. Our instructors, Joelle and Mike, were excellent and Katie in the office make sure everything was well coordinated. We were also surprised to meet Doris and Steve Colgate and the personal interest they took in our experience.
Joelle and Mike were awesome! Very patient and really took interest in our success. Both also went out of their way to make sure everyone was comfortable and safe. I wanted to write to thank you for all you did in setting up my trip. It ended up being a wonderful experience aboard the big catamaran. My instructor, Amanda, was extremely professional in all her teaching and guidance, and made the trip very pleasurable. She was very instructive and patient, and did a great job in giving me confidence to sail. I have now booked my first charter to take my family and friends to BVI this May.
My hat is off to all those people in your organization who have put together such a phenomenal program. It is no wonder you claim to be the 1 Sailing School in the World! Paul wrote: Overall a most enjoyable experience made all the more relaxing and fun with Brian. He created an atmosphere of calm and peaceful so as to lay the groundwork for the most learning possible. Brian is an excellent instructor, clear, concise, patient, engaging, knowledgeable and a pleasure to be around.
He is a credit to your school and as good as it gets for learning to sail. It was so enjoyable to learn so much and have so much fun doing it. Brian is a professional, knowledgeable instructor. His personality for this environment was perfect, with a warm and patient attitude. Both of my instructors, Brian in the photo with me on the Colgate, and Dutch on the live-aboard portion of my course, were excellent. They were calm, patient, and full of sailing wisdom that they imparted all throughout the experience so that the ideas being conveyed were always clear, relevant to the task at hand and became second nature by the end of the 8 days.
Fantastic experience. Hercules was a recreational Tardis. With the cabins below, and a deck and a cockpit up top, there was plenty of space for a family of five to spread out with books and iPods. And swimming in sea the colour of a Hockney pool. The snorkelling was wonderful, though there are far fewer fish than I remember as a teenager.
Every island told a story.
The Ionian sits at a crossroads where the sea routes along the Adriatic meet the east-west highway through the Gulf of Corinth. Romans and Corinthians, Venetians and French have all occupied the islands over the past 2, years, while the archipelago was variously mugged by Vandals and Goths, Saracens and Normans. In the s, the islands suffered an unhappy spell as a British Protectorate. In an earthquake killed people in the Ionian Islands and flattened most of the buildings on Kefalonia and Zakynthos. The history of the Ionian Islands is written in invisible ink; on the surface, you catch but the faintest traces.
In all, we sailed to eight islands. Uninhabited Atokos we visited one lunchtime, anchoring for a swim beneath precipitous cliffs. Inside, a gritty spiral staircase climbed to a parapet with views across the straits to Ithaca. Behind the lighthouse simmered the ruins of a Norman church. One night after an aborted attempt to find shelter in a full-to-bursting harbour on Kastos, we motored through the setting sun to neighbouring Kalamos, where Jack knew a beach protected from the wind by mountains.
Just in case the anchor dragged, I slept in the cockpit, drifting off to sleep as the masthead light played tag with the Milky Way. Throughout the voyage, the sailing was alternately sublime and exhilarating. Most mornings the breeze was soporific or absent while afternoons could blow up to about force five. And every day there were Odysseus moments aplenty, the currents of history tugging at the tiller as Hercules bounded across the blue Ionian under two bowed sails.
To reach Palairos, we took trains from London to Venice raileurope. A more direct route is a flight to Preveza airport. Airlines flying there from the UK include flythomascook. I booked our holiday with Nautilus Yachting ; nautilusyachting. The prices are for the whole yacht on flotilla regardless of the number of people on board within reason.