When we move and the wind also moves the total wind we feel is the apparent wind. Slight changes in true wind speed affect boat speed, and in turn, the apparent wind speed and direction, which can easily mask a small but important shift in the true wind direction.
The popular analogy is that of riding a bike.
We have seen cases where the masthead instruments are affected by updrafts from the sails, which is why some race boats use a rather large arm holding the instruments a good distance off of the masthead. As you might guess the other kind of wind, apparent, is the wind that is generated by our movement in combination with the true wind.
Iceboats, which have very little resistance between hull and ice, are very good at making their own wind and will often sail two to four times faster than the true wind.
It is the green triangle that you plot, i. By Staff What is the difference between true and apparent wind, and does it matter? When you're moving along and point to where the apparent wind is coming from, the real true wind will be coming from further towards the back of the boat.
So the sailor sheets in for the new wind angle and picks up more speed, further increasing the apparent wind and moving it even farther forward. As the boat points off the wind, lateral force and the forces required to resist it become less important.
But on light, fast boats-think multihulls and planing dinghies-it's a different story. Once you are being set off course and COG does not equal H, then the standard formulas for computing true wind from apparent will not work properly, because we measure the wind direction relative to H, but our actual motion is in direction of COG.
There is clearly logic in this terminology, and it drives home the point that we should think on these differences. Our actual use of compass directions in navigation does indeed complicate things a bit, but that can be sorted out later as it is not really related to the subject at hand.
It is the wind we feel when we are outside at rest and not moving. You just substitute SOG for the S that is in the equations or plotting routines. As the boat sails further from the wind, the apparent wind becomes smaller and the lateral component becomes less; boat speed is highest on the beam reach.
All sailing craft reach a constant forward velocity VB for a given true wind velocity VT and point of sail. Below is a sample computation of an extreme case of strong current showing how different the true wind results are if the COG-H difference is not accounted for.
Downwind, certain high-performance sailing craft can reach the destination more quickly by following a zig-zag route on a series of broad reaches.
The important thing to realize here, however, is that as you travel faster the apparent wind not only increases in speed but it also changes the angle of the wind.
That all works fine in those cases, and there are numerous resources online, such as the one included in what we call the NIMA Nav Calculators, which is a free download at www. He proposes to call this wind the Water Wind, as opposed to True Wind which as shown above is not correctand then do away with the term True Wind and call that Ground Wind.
It seems safer to get the answer from x-y coordinates, and so we present these formulas, written in a way that can go directly into a spreadsheet or calculator. The only time there is no apparent wind is when we are at rest and only feeling the effects of the true wind.
Symmetric spinnaker while running downwind, primarily generating drag. In big waves, you often expect the speed to be different on opposite tacks, but if the speed sensors and sail trim are working properly, the true wind should be the same on each tack or gybe.
In order to act like an airfoil, the sail on a sailboat is sheeted further out as the course is further off the wind. Ben Ellison has pointed out www. Ice boats and land yachts minimize lateral motion with sidewise resistance from their blades or wheels.
We know the true wind is 10 knots and, since we will be moving forward we will be producing 5 knots of wind ourselves. The spreadsheet format that computes everything will make it easier to experiment with various interactions of sailing and current to see how this affects the final outcome.
This is similar to a boat. On a boat this can be easily demonstrated and felt by first sailing upwind, and then bearing off to a downwind course. So we sail to the apparent wind, and not to the true wind. However, it is likely simpler to plot it with actual bearings, rather than as a relative plot using COG as Forces on sails depend on wind speed and direction and the speed and direction of the craft.
We see the combined effects of the true wind and our boat's motion forward. Depending on the alignment of the sail with the apparent wind angle of attacklift or drag may be the predominant propulsive component.
So there is a limit on just how fast a boat can go relative to the wind.
Thus, you can no longer simply work with apparent wind angle AWA ; you have to switch to using apparent wind direction AWD and solve the vectors relative to COG, as shown in the sketch opposite.
If we do not figure this properly, we can miss an important shift.Dec 16, · Captain John with 25+ years of experience shows you the no-nonsense cruising skills you need for safer sailing worldwide. Visit his website at bistroriviere.com That's apparent wind - it's what your hand feels out of the window and on a boat it's what the sails feel.
If you stop the car, the apparent wind goes back to be the same as the true wind. The true wind stays the same regardless of your speed. Slight changes in true wind speed affect boat speed, and in turn, the apparent wind speed and direction, which can easily mask a small but important shift in the true wind direction.
To help practically illustrate these points, let’s bring in some shorthand. This produces the apparent wind, what we actually feel while sailing on the boat. Boats always sail in the apparent wind. Here, note the apparent wind is stronger than the true wind (the arrow is longer) and is coming from further towards the bow.
Apr 03, · The faster the boat sails into the wind, the more the apparent wind speed increases and the more it feels like it is coming from the front of the boat. As a general rule of thumb then, when sailing the true wind is about 15 degrees more towards the back of the boat.
apparent wind Steve Colgate. Apparent wind is a very simple concept that continues to mystify many people who have been sailing for years. It is the combination of two winds: the one derived by the boat moving through the air and the wind produced by nature—the true wind. which would only be the case at different points of sailing if the.Download