Wind Speed Ebooks Catalog
The United Kingdom is in the process of developing offshore wind farms for the generation of electricity. It appears (2003) that these developments will be clustered in the following regions Wind farms may consist of 60 or more turbine generators spaced 200m or more apart. Cables connect the individual turbines to a separate offshore substation platform, which is connected by a cable to an onshore substation. The turbines are mounted on a tower on a platform connected to a foundation. The foundation may be a single pile sunk into the sea bed, an anchored tripod, or a caisson filled with aggregate the foundations may be surrounded by riprap to protect it from wave action.
Sailors around the world (whether they use the metric system or not) measure the wind speed in units called knots nautical miles per hour. A nautical mile is equal to one minute of latitude one of the horizontal lines on a chart or globe. (We talk more about latitude in Chapter 9.) A nautical mile is 6,076 feet, or 1,852 meters, 15 percent longer than a statute (regular) mile, so 10 knots of wind equals wind blowing at 11.5 miles per hour. Or if you're used to the metric system, 10 knots equals 5.14 meters per second or 18.52 kilometers per hour. Fortunately, you have another way to judge wind speed by looking at the water. Admiral Sir Francis Beaufort of the British Navy developed Table 8-1 in 1805. He must have been an observant guy (or bored stiff on long sea voyages), and sailors benefit from his perceptions still today. He defined wind speed in terms of a single number the Beaufort Force which is the first column in Table 8-1. In some parts of the world, weather forecasters still...
Compact unit measures wind speed from 0-150 mph. Patented ultrasonic technology no moving parts Works by tracking changes to an inaudible signal inside the wind barrel. Gives current wind speed, running average, max. headwind & tailwind, windchill. Exceptional accuracy, rapid response.
Vectors are underlined their magnitudes are not. Thus, boat velocity is v and boat speed is v. The apparent wind speed is w'. The angle between two vectors is generally denoted by the vector names, so that avw is the angle between boat velocity direction and apparent wind direction. where w is the constant true wind speed, a pAw m and, as earlier, 3 mb pA. 9. Because boat speed is small compared with wind speed (v w) for realistic values of hydrodynamic drag, I can neglect terms of order v2 w2 and so obtain an analytic expression for equilibrium speed. In fig. 4.5 I assume that two different strategies are used (two different mathematical helmsmen,'' H1 and H2) for trimming the sail. H1 is used to square-riggers, and he adopts the best sail angle of attack that we determined earlier for square-riggers a 90 avw 2. H2 adopts the following form a 90 avw (1 + avw 180 ). Of course, real helmsmen don't sit down with a calculator and set sails according to such trite formulas, but H1 and H2...
Another element of apparent wind is its angle relative to both a boat and the Figure 6.5 angle at which it is sailing since any change in wind or boat speed will have an When there is an increase in true wind effect on the angle at which the wind comes into contact with the sails. For exam- speed, the apparent wind angle will ple, when there is an increase in true wind speed, the apparent wind angle will increase. be pulled more toward the direction of the true wind (Figure 6.5). In other words, the apparent wind angle will increase. As you get higher off the water there will be more wind and therefore a larger wind angle so that, for example, when the bottom third of your sails is sailing hard on the wind the top third may be sailing on a close reach. If you want the whole plane of the sail to be efficient you need to turn or twist the plane higher in the sail to account for the increase in wind speed and change in wind angle. This is the essence of twist and the reason why sails...
When looking at the start you must consider the first beat. If one side of the race course is heavily biased, due to differences in wind speed (more wind) or angle (a wind bend) or strong current difference across the race course, it may well be worth considering starting away from what you would consider the favoured end of the line (see Figure 5.3a-d) to ensure you can work the favoured side of the beat
The force of the wind increases by the square of the velocity, which means that at 14 knots, the wind force on your rigging and sails is double the load on the boat at 10 knots. And that's before you add in the effect of the waves. Sailboats and their component parts can only stand so much load before they begin to break. And as we point out earlier in this section, stronger winds make your boat and sails more difficult to handle. As the wind speed increases, anything you do to reduce the forces on the boat in strong winds can make a big difference.
The area we sail in is called the boundary layer (the wind closest to the earth's surface) it is around 600 metres above the surface (there is no strict definition). Weather maps are for the top of the layer. They differ slightly from the bottom of the layer, where we sail, due to surface friction. However, there is a definite relationship between expected wind and the isobar spacing, so this can be very useful. (Surface wind speed will be reduced by up to 25 of the gradient and backed by up to 20 degrees over the sea. Over the land, wind speed may be reduced by as much as 75 and backed by as much as 40 degrees.)
In your mind's eye, try to imagine the wind flowing across your sails. If you have telltales, those small, light pieces of yarn or fabric attached to the surface of the sail, they will flutter in the air stream, dancing to their own rhythm dictated by the set of the sail and the aspect of the boat to the breeze. When these telltales stream in unison your sails are working efficiently when they move haphazardly you know it's time to change the trim. It's a delicate dance dictated by many forces and variables, one of the most important of which is the amount of stretch in the sail. If the fabric distorts, the shape of the sail changes and its efficiency is compromised. This balance between wind speed and sail shape is at the very core of sailmaking. It starts with a yarn, or more to the point, thousands of tiny yarns that form the basis of all sails. These fibers dictate the performance of the sail. So before we can explore the wonderful world of sailmaking, we first need to know and...
Once the bow has crossed the eye of the wind, the headsail needs to be let go, but not until it is back-winded for a second or two, since the pressure will both help push the bow of the boat onto the new tack and also push the sail through the foretriangle quicker. By this time, the headsail trimmer on the new side should already have taken up the slack on his sheet so that as soon as the sail is released he can start to pull it in on his side. Be sure, however, that the sail is not sheeted on too tight, too quickly, since that will cause the boat to stall. All this time, the mainsail trimmer will be working the main, sliding the traveler across and easing the sail so that when the boat is on the new tack the mainsail will not be over trimmed and stalled as the helmsman foots off ever so slightly to build speed. Remember that until the boat is back up to speed the apparent wind speed is going to be a lot less on the new tack than it was on the old one, so be sure that the main is...
Airflow over water is always a bit turbulent, so even the steadiest conditions have little wind shifts, or changes in the wind's speed and direction. When you're sailing near shore in an offshore wind, the wild shifts in the wind speed and direction can be downright maddening (although the racers in Chicago's downtown Belmont harbor claim they can predict the wind shifts by watching the doorman open the door at the waterside hotel ). The following are some common types of wind shifts
There are several things you can do to reduce jibing loads. The first is to jibe at the point when the boat is accelerating down a wave. This reduces apparent wind, and since the force on the rig is a function of the square of the apparent wind velocity, small changes in apparent wind strength make for big changes in loading.
Heavy weather and heavy air are sailors' terms for a strong breeze. As you find out in Chapter 8, sailors measure wind velocity in units called knots and can estimate the speed of the wind by looking at the water's surface. We recommend that a beginning sailor head for home when whitecaps (foamy wave crests) become commonplace, or at about 15 knots. But for an experienced sailor (especially on a high-performance dinghy or catamaran), 15 knots of wind is when sailing gets fun.
The months from late June through November bring fierce tropical cyclones, rarely passing south of 15 degrees N.(Cabo Gracias a Dios). September and October are the most dangerous months with highest frequencies, wind speeds and forward speeds. Between these storms it is normally hot and calm except for occasionally strong thunderstorms with high winds. They do not last long and radar is useful in maneuvering to avoid them. Power yachts with long range at good speeds and operated by knowledgeable and vigilant professional captains make their best passages in the summer.
There are two more points you need to consider when it comes to draft location. First, always remember that with sail trim, any action will have a corresponding reaction, and sometimes the effect might be bad for boat speed. For example, draft-aft sails mean that the back end of the sail will have more curvature than you might like and the air flow may become separated from the sail, causing it to stall. In light or moderate winds this is not a problem. But in a near calm or as the wind rises, it may be. Second, remember that because there are different wind speeds flowing across the sail from top to bottom, the location of the maximum draft will differ from top to bottom as well. Specifically, the draft down low will be further aft than the draft up high, because the increased wind up high will drag the apparent wind angle aft, meaning that you need a fuller luff entry. You need to understand these differences, but if the sail has been designed properly you should not have to worry...
Candidly, my suggestion is that you do not try going east. The wind systems simply were not meant for that direction. But if you insist and do not want to bash into a headwind, nor rush into a cyclone, I can only suggest using the spring and autumn calms at which time it is best to motor as hard and as fast as you can.
That you can either fire the tack and do a regular takedown under the boom, or douse the spinnaker by lowering the hoop on the dousing sock. To do the latter you should bear away gently until the apparent wind angle is around 150 degrees. At this point of sail the apparent wind speed will be at its lowest, and the spinnaker will be starting to collapse from the leech first in what is called a leeward break. Usually the spinnaker collapses when the luff folds over, but if you are successful in getting the sail into the dead air behind the mainsail the spinnaker will collapse from the other side. This is caused by the confused flow of air behind the mainsail sucking the leech in toward the sail. At this point your spinnaker is as tame as a puppy and you should be able to either lower the hoop down over the sail or let the tack line go and drop the sail to the deck. Never attempt to douse the spinnaker when the wind is on the beam unless the situation on the race course gives you no...
The difference On the first crossing, the tide was flooding 1 or 2 knots to the north, running in the same direction as the wind. On the second, the tide was ebbing, opposing the wind at only a knot or so. The difference in the seas, however, was truly exponential. This difference can't be explained simply by adding the water speed to the wind speed to get the wind-overwater speed, although that does make matters worse.
The Stone Horse 23 (named after a shoal in Nantucket Sound) was designed some 75 years ago by New Englander Sam Crocker as a fine little cruising boat for two people. Although on deck she measures seven to ten inches shorter than her comps shown below, she is right in the thick of her comps' stats, except that she sleeps an honest two rather than four, if you discount the two children's quarter berths. She is cutter-rigged, giving her a wide choice of options in whatever wind speed and direction she finds herself. Her anchor can be rigged and
One of the first things you notice is the lack of heeling on a cruising cat. There's no need for constantly bracing yourself or your gear at unnatural angles. Sailing is more comfortable and less tiring which translates into greater enjoyment and safer operating conditions. Searching for a downside to level sailing, I'd say there's a lack of feedback that heeling provides the helmsman. With no appreciable heel and a reduced tendency for weather or lee helm on a cat, it's more difficult to tell when it's time to reduce sail. One must rely on boat speed and boat motion relative to the seas. Multihulls have no real ability to spill a gust of wind by heeling they typically translate excess wind energy into acceleration, which demands Cruising multihulls not only accelerate quickly, but they maintain higher average speeds than monohulls. In moderate conditions, even slower cruising catamarans sail as fast as monohulls, and attain higher top speeds in fresher conditions. Highperformance...
In chapter one we derived an equation for the ratio of boat speed to true wind speed where y and are the course angles to the true and apparent wind vectors respectively. We want to be able to predict the speed of a boat on any course angle y subject to a given wind speed VT, thus we shall consider VT and y as known input variables. The quantity pA 1.19 10 3 slug ft3. The apparent wind speed VA can be expressed in terms of VB, VT and y,
Sailing boats exploit the discontinuity in fluid flow that exists at the air water interface in order to propel themselves. We may consider the water to be at rest and describe the velocity of the wind by a vector VT. The magnitude of this vector is equal to the wind speed with respect to the water and the direction of the vector coincides with the wind direction. Under the influence of the wind, the boat moves at a speed VH in a direction given by the vector B. Motion of any object through still air with a velocity B gives rise to an induced wind velocity - V0 in the opposite direction, hence the total or apparent wind velocity felt by the boat is the vector sum of the true and induced winds, that is For a given boat, these drag angles are a function not only of y, the course angle, but also of VT, the wind speed. The data given in Figs. 1-5 and 1-6 was taken for wind speeds in the 5-10 knot range. At higher wind speeds, heeling and the need to reduce sail area causes dA to increase...
As an air brake if streamlining considerations are not taken into account. Designers therefore try to restrict freeboard to the minimum necessary. Windage can greatly affect a fast catamaran's performance and the wind pressure experienced by the vessel's hulls and superstructure can be considerable. One should not forget that the force is proportional to the square of the wind speed. This means that an increase in boat speed from 5 to 10 knots will result in an aerodynamic drag that is four times more. At 15 knots of boat speed the drag is nine times more than at 5 knots
The farther downwind your destination is the more it pays to perform a series of gybes. This is especially true in winds under 15 knots true. VMG or speed made good towards your goal is an important concept to understand. It is inherently associated with Apparent Wind and your best boat speed as compared to sailing a certain course. The skipper's decision whether or not to diverge from the Rhumb Line will depend on the wind speed, the sea state and the multihull's polar diagram. Generally, in light air, multihulls will go appreciably faster if the Apparent Wind is brought forward. This means if you are sailing on a broad reach, it will pay to steer upwind and sheet in, especially if the wind is fluky and inconsistent. Heading changes do not have to be excessive. A course correction of only 10 degrees could make a substantial difference, resulting in an increase in Apparent Wind pressure and 2 knots more speed. Needless to say other parameters, such as un-navigable areas, vessel...
*The official world record for iceboat speed was set back in 1938 by John D. Buck-staff on Lake Winnebago, Wisconsin. His craft Debutante glided over the ice at 147 mph. According to Encyclopaedia Britannica, iceboats can achieve speeds ''at least four times'' the wind speed when sailing across the wind. To see how much better the Bermuda rig performs, I must bite the bullet and tackle the full equation of motion, which some of you have already seen in note 4 but which I have avoided in the text until now. In fact, by confining my attention to the equilibrium speed I avoid calculus and am left with algebra, which is easier. The results are shown in figure 4.5. Here, the approximate equilibrium angle9 for a Bermuda-rigged boat (characterized by the realistic lift and drag curve of fig. 4.4) is plotted for different wind directions, from running with the wind to close-hauling. According to my analysis, Sparrowhawk can sail to within about 20 of the wind, though she will make no headway....
Speed and direction of travel of the boat and the True Wind. True Wind is the direction and force of wind we would feel when stationary. Say you are sailing at 7 knots and experience a True Wind from 90 degrees off the starboard beam. The resulting Apparent Wind would be 12.4 knots. This would mean that you (and the sails) would be feeling 12.4 knots of wind pressure. With the same True Wind Speed however, sailing directly downwind at 7 knots, the boat would only feel 3 knots of Apparent Wind, as a large portion of Apparent Wind is cancelled out by the forward speed of the boat. In the table below, it is clear that at 45 degrees the catamaran will achieve its highest VMG at 8.5 knots. Every multihull has a different sweet spot at varying wind speeds. The boat's polar diagram and vessel heading will be decisive factors towards the choice of course to be taken.
In the Bay of Bengal wind speeds over the open sea in July are generally Force 4-6 (10-25kn) although there will be occasional days of Force 7 and possibly 8 (30-40kn). In June and August wind speeds are a little less. In the Arabian Sea wind speeds over the open sea in July are generally Force 5-7 (18-32kn) although there will often be days of Force 7-8 (30-40kn). In June and August wind speeds are a little less but still substantial and there is more than enough wind to shift you along.
We have seen in Chapter 3 that when the true wind is blowing across a moving boat, the apparent wind which results is affected not only in strength but also in direction. It always comes from forward of the true wind until the boat is on a dead run. With the wind well aft, the apparent wind speed will be less than the true wind. As it approaches a point just abaft the beam they may become similar, and as the true wind comes onto or forward of the beam, the force of the apparent wind will always exceed it.
Be very uncomfortable because of the confused swell generated by the trade wind systems meeting at that point. It is therefore recommended to try and stay with the NE trades north of the equator and only cross it in longitude 29 W or 30 W. A more westerly crossing point is not advisable if making for Salvador because of the risk of headwinds south of the equator. See also AT10 and AT15.
Next, in unstable conditions and or with the mean wind speed above 20-knots, we stay with a single or twin jibs. As the wind angle goes more towards a broad reach from a run, we can carry the spinnaker in a bit less wind at the lower end of the wind speed spectrum. However, because of stability and control limitations, as the wind goes forward the top wind speed in which we carry the chute comes down too. We are happiest using the spinnaker between 8- and 16-knots of true wind speed on a broad reach.
A modern boat swept by seas coming at the bow tends to pivot on its center of lateral resistance, sometimes known as the center of lateral plane (CLP) or the center of lateral area (CLA). This underwater center tends to be aft of amidships, and the pivoting motion is augmented by the windage of the forward-placed rig and especially the bulk of a roller-furling headsail. A rolled-up headsail with a luff measurement of 45 feet and an average diameter of 5 inches has an area of almost 20 square feet. These two forces impart a turning motion to push the bow sideways to the wind. Remember, the force on a given area increases with the square of the wind velocity as the wind speed picks up.
The best way to sail from one hemisphere to the other has preoccupied mariners ever since early explorers discovered the zone of calms that separates the trade wind systems of the two oceans. 'The well known equatorial embarrassments' is how Alexander George Findlay refers to the doldrums in his Memoir of the Northern Atlantic Ocean published last century, a comprehensive book in which he tries to bring together all that was known at the time about the wind systems of the North Atlantic. The best strategy for tackling the doldrums is discussed in great detail, because fast passages across the equator were still of utmost importance to the masters of sailing ships linking Europe and North America with the rest of the world before the opening of the two great canals and the proliferation of powered vessels.
Stubbornly try to follow the direct route between two points. This is the reason why it is so important to understand the prevailing wind systems of the world, which dictate most of the cruising routes described in the following pages. 'It has been well observed that the wind systems of our globe naturally govern the tracks of ships crossing the oceans, the trade winds carrying them from East to West within the tropics, while anti-trade or passage winds Winds and Currents of the World i Prevailing wind systems January to March Winds and Currents of the World i Prevailing wind systems January to March 2. PREVAILING WIND SYSTEMS JANUARY TO MARCH f Prevailing wind systems April to June 3. PREVAILING WIND SYSTEMS APRIL TO JUNE Prevailing wind systems July to September Prevailing wind systems July to September 5. PREVAILING WIND SYSTEMS OCTOBER TO DECEMBER Prevailing wind systems October to December Prevailing wind systems October to December In many areas these systems are distorted by...
Planning an offshore voyage is not a simple matter because many factors have to be taken into consideration. The most important factor to be considered is the safety of the vessel and its crew, therefore it is crucial to ensure that the route will avoid areas of known dangers and also that as much as possible of the sailing will be done during favourable seasons. A large proportion of the cruising routes described in this book are in the tropics, which is where world voyagers spend much of their time. However, many tropical areas are only safe for six or seven months of the year, the remaining months being liable to tropical storms. In the following pages I shall try to give some examples of typical world cruises that can be done with maximum safety. The various circumnavigations described are all westabout to take maximum advantage of the prevailing wind systems and to sail as much as possible under trade wind conditions. Because much of the time will be spent in the tropics, the...
The appeal and challenge of sailing arises, in part, from the enormous variation of conditions that occur as the wind speed varies from calm to a gale. A typical sailboat's speed is comparable to the wind speed, so calms produce bored and frustrated sailors, while a really strong wind results in panic. A knot is the historical nautical speed unit. In the old days (perhaps all the way back to the Netherlands in the 1500s), a series of knots were tied on a rope, separated by about 15 m. (A meter is a little more than a yard.) The number of knots paid out to a fixed point in the water in about 30 s gave the boat's speed, U, in knots. Wind speeds, W, are also often quoted in knots. A qualitative characterization of wind speed is the Beaufort scale, developed around 1800. This scale places wind speeds into about a dozen categories. A modern refinement of the Beaufort scale relates the Beaufort numbers, B, to the wind speed, W The Beaufort number B 5 is called Fresh Breeze. Many small boat...
Wind is wind, so whether it is true wind or apparent wind it still has the same effect of an air mass hitting a boat's rig at a given wind speed. Therefore, if a boat goes faster it gets more wind. Lightweight skiffs tend to sail fastest on a run by sailing as fast as possible. This creates more wind (air mass hitting the boat) and the effect is better velocity made good (actual speed towards the next mark).
This is probably the single most important feature of any sail. The chord depth, also called the camber or draft, is determined by running an imaginary line or chord from the luff of a sail to the leech (Figure 6.1), and then measuring the distance from this line to the deepest part of the sail. The chord-depth ratio, often expressed as a percentage, refers to the ratio between the length of the chord and the depth of the sail. Because sails taper toward the head, it is important for the draft of the sail to be expressed in terms of a ratio rather than a measurement. A depth of 18 inches in the body of the sail could be seven inches toward the head and still have the same chord-depth ratio. Note that chord depth can be adjusted by the way you set your sails and that there is no one chord depth that is perfect for all conditions. Rather there is a chord depth that is right for a given set of conditions taking into account wind speed, wind direction, wave heights, the kind of boat you...
Cylinders of around 0.1 m diameter with different roughness heights. The height is given as a percentage of the diameter. It may be seen that at 11 m s the drag is reduced by 50 if the roughness height is 0.5 of the diameter. The more narrow wake also disturbs the sail much less, so there is a double gain. Unfortunately, the optimum roughness height varies with the wind velocity, but a height of 1 covers most of the interesting velocities quite well. Note that it is the apparent wind that is of interest.
This is a time for the sail trimmers to be planning and anticipating the first few legs of the race. Might there be a need for an outboard lead on the genoa Is the breeze building Will the crew have to throw in a reef What are the settings for luff and outhaul tensions Check your notes and make sure that the sails are set up for perfect trim the moment the start gun fires. Ask the navigator what the apparent wind speed and angle will be once you get around the top mark and think about what spinnaker you will need. If you can anticipate changes before they hit you, you will be much better prepared to deal with them. Keep your sails powered up outhaul off, lead forward, and so on if the helmsman needs the power, but remember that it's more important to have the sails trimmed perfectly when the start gun fires rather than in the pre-start maneuvers. The helmsman is going to need all the power and speed he can get to place the boat exactly where he wants it when the gun goes off and it's...
The following morning, 0400 hours, and we are approaching Point Saint George just north of California's Crescent City. It is the end of my watch, and I am thinking about our potential sub-three day passage down the 1050 mile coast line. As if he has just read my mind Aeolus turns off his wind machine. So much for a record passage.
Wind generators Wind generators work well when they are in a predictable upright position. The high apparent wind speed of a multihull also improves their performance. The windage and weight of wind generators reduces their popularity on racing multihulls and at high speeds they also produce a moderate noise.
You may think that zero twist has the most power, but that's rarely the case, because of a phenomenon related to friction. At and near the water's surface, friction noticeably slows the true wind as the wind rubs against the water and waves. Moving up toward the top of the mast, the true wind speed increases. This vertical variation in true wind speed causes a situation of great interest to sailors the apparent wind felt at the bottom of the sails is farther forward (more from the bow) than the apparent
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In any given wind speed, if a boat is accelerating, the lift forces that are moving the boat forward must be greater than the drag forces that are holding it back (Figure 15.8). These forces apply to both the sails moving through air and the underwater appendages, i.e., the rudder and keel moving through water. The proportion of lift to drag is fundamental to a boat's performance and should always be remembered when trimming sails or balancing a boat for optimal performance. The late Bruce Banks, founder of Banks Sails, once wrote, Only sails drive the boat forward, everything else is holding it back. It's a sentence well worth remembering if you are looking for performance.
Trimming and shaping sails, and seeing the resulting gains in performance, is one of the more rewarding aspects of our sport. But with the wrong cordage, a sail will forever change its shape with changes in wind speed. When the sail changes shape, you lose power. If you've recently upgraded your sail inventory, but neglected to upgrade your sheets as well, you're selling yourself short match your ropes to your sail material and the power in the wind will be turned directly into boatspeed.
One of the most spectacular forms of sailing, called flying the hull, is available to catamaran sailors. It takes place when the upwind hull is actually raised off the water by the heeling force on the sails. If allowed to go too far, flying can result in a capsizing, and you've got a long way to fall from the upwind side of a cat. But kept under control by steering slightly into the wind to luff the sails (or away from the wind to reduce the apparent wind speed) and hiking out on the windward side, it's an effective tactic for balancing a catamaran. (Hiking out is hanging off the high side of a sailboat when it heels to help keep the hull upright through moving the center of gravity to windward. Hiking straps across the trampoline secure your feet so you don't fall overboard.)
Strategy will vary a lot from class to class and depend upon the wind's strength. For example, in marginal planing conditions (for a particular class) wind speed may be the most important factor. On a shifty day, being on the right tack may be the most important thing. However, if the wind speed and current speed are similar, current will be the deciding factor if there is a difference in water flow across the race course (especially for the slower boats or those which lose a lot of speed tacking). Wind speed across course Wind speed across course
Experience with ultralight displacement boats (ULDBs) of all sizes has shown that the speed potential of these flyers is just too great to be effectively entrusted to windvane steering. Every change in wind speed aboard such responsive boats produces a change in boatspeed which, in turn, changes the apparent wind angle. The acceleration and deceleration of the boat through puffs and lulls causes the apparent wind angle to move forward or aft. A windvane gear steering to a particular set wind angle would as a result have to head up or bear away every time the wind speed changed in order to maintain the set angle.
The rake of the mast is usually available through the class association. Remember, with all these rig set-ups you need to 'get your head out of the boat'. If conditions gradually change (the water becomes flatter, the wind speed increases, wave length increases, etc.) you need to adjust your rig If you are using different sails you will need to set up the mast differently. The sailing characteristics of a full sail on a floppy mast are very different from flat sails on a stiff mast. If the conditions are constantly changing, you need to be constantly changing the rig so that it is optimised for the conditions. If the conditions are constant, set your rig as best you can and then leave it, so you can concentrate on other things. When conditions are constantly changing you need a set-up which is easy to sail (in other words, it is easy to point, foot and make the boat go fast in a range of wind speeds).
The very first sailing physics topic that I need to convey to you is the idea of apparent wind velocity. This notion is absolutely fundamental for an understanding of sailing vessel movement. Fortunately, it is a simple idea and one that already will be very familiar to those of you who sail. I will state the case, nevertheless, because we will require the concept very soon when seeking to understand how wind provides drive for square-riggers. Even if you are thoroughly at home with apparent wind, there may be something for you to learn in this section, and it will serve to tell you about my notation. and in what direction it is moving. So, in figure 2.2a the arrows represent wind velocity, whereas the arrow lengths represent wind speed. The angle between boat velocity, v, and true wind velocity, w, is avw. (Throughout the book I will denote vector quantities like velocity with underlining.) The wind velocity felt by the moving boat is not w but rather w W v the boat moves through the...
For all boats there is a certain wind speed beyond which the full-sized sails need to be reduced in area if the boat is to be kept sailing efficiently. There are no firm guidelines which can be given to help you decide when to reduce sail it is a decision for the skipper to make on the basis of the type of boat, the experience of the crew and the conditions. The only advice which can be usefully given is that the boat should be sailing with no undue strain on any part of it. If it becomes clear that the boat is overcanvassed for the conditions, the sail area must be reduced. The headsail area can be reduced either by changing to a smaller sail or by reefing, but the mainsail can only be reduced by reeling unless the conditions are very rough when a trysail can
Think about how the boat 'feels' you need to be constantly pushing the boat up to gain extra speed. As soon as you are not increasing the pace by coming up further, then keep that height. As the wind speed increases and decreases the optimum angle can change significantly. Also remember that as hull speed increases, so does apparent wind, meaning you need to sheet in more (and, of course, sheet out when the speed comes off and apparent wind reduces). You may find when the boat is at full pace you can bear away slightly without losing speed. Do this to maximise VMG (velocity made good, or simply the speed for getting close to the next mark).
In moderate conditions, tacking is straightforward. The traveler must be centered and the vessel must be sailing as close-hauled as possible. It is surprising how often one sees sailors trying to tack a multihull from a reach. This frequently fails, especially when the winds are light and the sea is choppy. In light air you should put the helm down smoothly and sail through the turn. The lower the wind speed, the more essential it is to be sailing upwind at full speed, just before turning through the wind. In very light conditions and or in lumpy seas, it might be necessary to sail an acceleration curve starting with a reach, and sheeting in to close hauled as one is gaining speed. Depending on windage and sea state it might be helpful to briefly backwind the jib, before sheeting in on the new heading. This will assist the bows in turning through the wind. Key to a successful tack is the skill of quickly sheeting in the jib on the new heading. If the boat feels like it is going to...
Turn to windward at 6 knots, the apparent wind speed would rise to something in the order of 45 knots. Because wind force increases as the square of its velocity, the force on the sails - from such an airstream - is virtually double. Alarming surprises await those who ignore this rule.
Docking under sail alone is no easy matter and your movements will have to be very carefully judged. If you are practicing, pick a day with medium strength winds and keep the engine running in case you get into difficulty. The success of the operation depends on your ability to handle the boat under sail at slow speeds, as well as having an efficient crew who can respond quickly to instructions. The wind shadow effect from harbor walls, buildings and other boats will affect wind speed and direction. This might easily wreck an otherwise perfectly planned approach and any good skipper
It is important to know the sideways drift rate in different wind speeds and the drift angle. Almost all single-stick sailboats drift with their bows angled to leeward 30- to 40-degrees. This angle is reduced if you get rid of roller-furling headsails. Sideways drift will vary with wind velocity, the wind gradient (how much more wind their is aloft than at water level) and with any waves that may exist.
The movements of individual depressions do not conform to a tight stereotype. However, by studying averages over a period of years it is possible to draw some general conclusions. In its first day or two of life, the vertical development of a depression is comparatively modest and is unlikely to penetrate the jet stream wind systems of the upper atmosphere. Because it is not interfering with these, the young 'low' will tend to move along their general direction, which more often than not is northeasterly. As it matures, the system extends its influence higher and higher until it is distorting the upper winds. It will probably then slow down and may turn from its straight track usually, but not always, to the left. Ultimately, as we shall see, the circulatory mechanism stalls and decays.
The mainsail also creates somewhat of a slot effect at the very end of the head-sail where the air is squeezed between the leech and the lee of the main. This is not the large slot effect that earlier studies pointed to because the circulation around both sails negates each other to some degree. But the wind does still speed up as much as 30 percent. In fact, studies have shown that the air coming off both sides of the headsail has an increased velocity and the Kutta Condition is met not at the free-stream speed, i.e., the speed of the external flow, but at a faster speed, again providing even more lift to the overall sailplan. Now isn't that interesting Who would have thought that the mainsail not only provides some lift of its own, but also makes the headsail more efficient by allowing the jib to operate in its own area of increased wind speed without the danger of violating the Kutta Condition
To sum it up, reefing depends on the force of the wind, the sea state, point of sail and the capabilities of vessel and crew. Above all, remaining humble and respectful of the elements will make you a better sailor. Following wind speed benchmarks will assist in determining when to reef which sail. Sustained Apparent Wind Speed
Wind speed, and true wind angle on the left side. I then put current set and drift, depth, course over ground, and speed over ground in the center. Tactical functions are on the right time to layline, time to waypoint, distance to waypoint, and TWD or TD (True Wind Direction) Angle of the wind relative to the surface of the water TWS or TS (True Wind Speed) Velocity of the wind relative to the surface of the water TWA or TA (True Wind Angle) Angle of the wind relative to the centerline of the boat AWS or AS (Apparent Wind Speed) Windspeed measure by the boat's anemometer AWA or AA (Apparent Wind Angle) Wind angle measure by the boat's anemometer Vs (Velocity) Boatspeed
A trolling generator means that when you're sailing at 5 knots you'll be generating enough electricity to run lights, ham radio, sat nav and possibly refrigeration, though not all at the same time, wind generators require more attention and can't be left unattended. Source for the Redwing Downwind Marine, 2819 Canon, San Diego, CA 92106, 619-224-2733. Additional source Hamilton Ferris, Box 126, Ashland, MA 01721, 508-881-4602.
DIFFERENT WIND SPEEDS Ultimately, the difference comes down to a contrast in power and wind speed. In other words, there are lots of things that airplane wings can do that sails cannot do, simply because of the power supplied by an airplane's engine and the speed of the air flow over the top and bottom of the wing. Made of thin pieces of fabric or membranes, the pressure differentials generated according to the classical theory of sail dynamics would never be enough to carry a sailboat through the water. In order for a sail to function there needs to be something more.
Generally, the spinnaker and gennaker are the two types of sails which are utilized for downwind or reaching conditions. Which sail to choose will depend on your intended course, wind speed and sea state. Both types can be very powerful so they should be treated with respect, especially when one is sailing short-handed. The ability to furl them at any time is imperative. Wind Speed, which brings the Apparent Wind to zero and causes the headsail or spinnaker to temporarily collapse. A spinnaker in that situation may wrap itself around the headstay. If it wraps tightly, you may need to gybe the mainsail to allow it to release itself. When freed, gybe back to your original course. You can help prevent spinnaker wrap by temporarily over-sheeting until the Apparent Wind picks up again. Repeated surfing and cavitation of rudders might indicate that you have too much sail up for the wind and sea conditions.
If you want to get the best performance out of your boat you will have to consider ways of increasing the driving force of the sails and reducing the drag caused by the hull and standing rigging. For all boats, there is an optimum wind speed at which the heeling force of the sails is just balanced by the crew's maximum righting power, when sailing upwind. Because upwind sailing tests the efficiency of the rig, you tune your boat for best performance on that point of sailing. However, you have to make the decision before sailing about what strength of wind you are likely to encounter. You must then increase the driving force of the sails for winds below the optimum and reduce, in general, the heeling force for wind speeds above it.
Usually daggerboard catamarans have a higher aspect ratio and are deeper than equivalent length monohulls since daggerboards are retractable and have no draft considerations. It is not surprising to see that in wind speeds starting at around 10 knots, a well-designed and sailed daggerboard cat will often outpoint and outpace a performance monohull. Even well-sailed keel catamarans often arrive earlier at an upwind destination compared to heavy monohulls. The few degrees they sacrifice of their ability to point to windward is often made up for by their higher speed and VMG (Velocity Made Good). This performance difference increases proportionally to the wind speed and is very noticeable in F4 conditions and beyond. Keels offer advantages - they do not need to be operated at all. They do their work silently, making one less thing to break. On the other hand, people who have never sailed with daggerboards think their operation is complicated. In fact, they are as easy to use as outhauls...
On any course save dead downwind, the speed of a sailing boat with respect to the true wind speed is determined by J, the angle between the velocity vector of the boat and the apparent wind vector. The smaller , the faster the boat. The course theorem Eq. (1-5) shows us that can be thought of as the sum of two angles, the aerodynamic and hydrodynamic drag angles, which in turn depend on the lift-to-drag ratio of the above water and below water parts of the boat respectively. The problem to be solved in designing a fast sailing boat is just the problem of maximizing these lift-to-drag ratios for all conditions of sailing in a manner consistent with seaworthiness of the boat and the necessary comforts for the crew.
The Velocity Prediction Program (VPP), mentioned earlier, may also be regarded as a module of the CAD system. As explained above, this program computes the speed, heel angle and leeway angle at all wind speeds and directions of interest, based on a set of dimensions for the hull, keel, rudder and sails. The very simple performance estimator, based on a few main parameters and used in the first iteration of the design spiral, may also be a module of the system.
Wind velocity could determine crossing times, and ice, the length of the navigation season but those were not the only significant effects of these two climatic factors. Although head winds would force a vessel to bear, or zigzag, thereby lengthening the distance, exceptionally strong winds were just as detrimental, if not more. Galeforce winds and the storms usually accompanying them were probably the greatest fear of transAtlantic crews and passengers of the day. When gales struck, the crew had to reduce the sail area to withstand the buffeting. Winds and waves made handling difficult and sometimes carried equipment overboard. Such a situation was described by Captain Joseph Huault of the schooner Aimable in 1755
The higher the wind velocity, the more you should downhaul. 2. The higher the wind velocity, the more you should downhaul. True. In higher wind the boat will fly a hull too high, the windward hull should be just kissing the water. As the wind increases, first single then double trap. If you still can't hold the boat down, increase the downhaul, which will cause the top of the main sail to twist off and reduce the force lifting the hull. This will allow you to remain sheeted and retain power and shape in the bottom of the sail. Spilling the top slightly reduces power, but significantly reduces the heeling effect of the top of the sail. 4. On a sloop rig the outhaul should be tight all the time when beating. True. You need a flat sail for sailing up wind, but just how flat depends on wind velocity. The higher the wind the flatter the sail in light winds a slightly fuller sail is required and thus the outhaul should not be pulled as tight.
Their specialty is DC power and die-sel injectors. They can test, diagnose, charge and sell batteries, dispose of your old ones, and check out your charging systems. They repair alternators and chargers as well as DC motors and wind generators. Solar panels are also available, as well as monitoring instruments. They will tackle any kind of electrical job on a yacht and you can also walk in for good advice, and buy many electrical fittings. If you need your injectors tested, they can do it on the spot.
On a soft luff, typically flown from a bowsprit. They are sheeted to a block way aft on the outside rail and, depending on the wind speed and sea state, can be flown from a range of 45 to 170 degrees of apparent wind angles. Unlike the genoa and Solent, they cannot be reefed. Usually they employ a Spectra luff and need careful attention when it is time to take them in. Similar to reefing a multihull's mainsail in stormy conditions, and in exact contrast to our instincts, multihulls should have the wind aft of the beam when furling them. This will reduce the pressure and apparent wind, and make the operation manageable.
The Flettner rotor* was developed in the 1920s as a radically different way to propel boats and ships via wind power. A vessel propelled by this strange mechanism is shown in figure A.14. It looks more like a giant floating candlestick than a boat. The idea is that the vertical column, which has a roughened surface, rotates and carries air with it as a result of the Coanda effect. Here, we have another example of Galilean relativity it doesn't matter if the air moves and the airfoil surface is stationary, or if the air is stationary and the airfoil moves. All that the Coanda effect requires is relative movement between air and airfoil. In fact, in our frame of reference both air and airfoil are moving the air moves at the wind speed, and the rotor moves at a controllable rotation rate.
In Fig 5.1 the apparent wind direction is marked by a fat arrow. This is not the true wind direction, since the wind felt onboard the yacht is influenced by its speed through the air. Fig 5.2 illustrates the relations between the true and apparent wind speeds and directions, the so-called velocity triangle. Note that the wind created by the yacht speed (which must be used when adding the wind vectors) is opposite to the arrow-shown as yacht speed in the figure.
Spinning, create bands of low pressure at the equator and mid-latitudes, with bands of higher pressure at the poles and subtropics. These pressure bands produce stable wind systems over the oceans, which are disrupted by temperature changes over land. The spinning Earth makes northern hemisphere winds incline to the right and southern hemisphere winds incline to the left.
You might choose to buy a published yacht log book, with entries for all sorts of information, or you may prefer to make up your own from a stiff-backed exercise book ruled off into columns. Professional yachts should have no difficulty in keeping a comprehensive log book. After all, they have plenty of crew and in the event of an inquiry into some incident on board, all manner of information may be required. Aboard a large yacht operating under the MCA Code of Practice, therefore, columns should be drawn up for Zone Time, Log, Distance Run and, perhaps, Distance to destination. In addition, Course Steered, Log Speed, GPS Speed, Lat Long, True and Apparent Wind Speed and Direction, Sea State, Weather and Barometer. These are a suggested minimum. If no dedicated engine log is being run, Engine Hours and Fuel Remaining columns may also be needed. Following all this hard data come the Remarks. One double page spread per day is a sensible layout, with the date and voyage details at the...
If the wind strength is rapidly fluctuating or changing direction reef as you would for the maximum wind speed in the gusts. When overpowered in a gust the correct action is to bear away and ease the sheets. Never luff up as this increases the apparent wind speed. By bearing away you effectively reduce the apparent wind and ease the pressure on the sails. As soon as the gust passes it's time to reef.
Generally, you want a fuller sail in light conditions when sailing through choppy seas on a heavy boat. Wind speed, sea state and boat weight will be the most important parameters when looking to power up. Consequently, the opposite is true when sailing in flat water in stronger winds with a light boat. All three factors, or a combination thereof, should dictate the degree of fullness the main and jib should have. Of course, outhaul, halyard, Cunningham, traveler and sheets will have the greatest cumulative effect, yet batten tension will contribute its share. The more the battens are under compression, the more they will bow and the deeper the chord of the sail will
With regard to rule No. 1, momentum has a lot to do with sail trim. Therefore, if you have an old-fashioned, long-keel, heavy, sea-kindly yacht, you can rely on inertia to keep you moving through the water once you have been able to get it up to speed. Subtle differences in wind speed and sail adjustment have little effect, and you do not need to be trimming constantly. On the other hand, a light, responsive, fin-keel boat will not be able to keep up speed if the wind drops or if it hits a wave and slows down. Those kinds of boats require a lot of changing gears to keep them moving well, and these gear changes are the result of the way you power up and depower your sails.
Since the speed of sailing craft is dependent on wind speed, there will often be conditions of relatively low boat speed (below displacement Froude number of 2). So it was recommended that a prototype design would have a retractable hydrofoil system which could be engaged in suitable conditions (sufficient boat speed).
Renewable Energy 101
Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.