Upwind Theory

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Upwind sailing can be a real challenge, and is an aspect of sailing that takes a lot of practice and patience to develop.

Some may initially find it a little difficult to grasp the concept of upwind sailing, but with the aid of vectors indicating the forces applied the process can be explained a little easier.

Upwind Theory – the forces on a boat

As in the diagram below, when wind enters the sail, it is forced to curve around the belly of the sail. This curve in the sail can be represented by a force (call it wind force ‘w’) acting at 90° to the sail. This force ‘w’ is made up of 2 components – 1 acting sideways on the boat (call it ‘s’), and another pushing the boat forwards (call it ‘f’). By using a fin, we minimize the amount of sideways slippage, and maximize forward motion.

Forces on a boat when sailing upwind

Forces on a boat when sailing upwind

You can see that the more you pull the sail in and sail upwind, the smaller angle ‘a’ will become, which will result in a smaller force ‘f’. The smaller the forward force ‘f’ pushing the boat, the slower the boat goes. Conversely, the more you bear away and let the sail out (up until the point before it starts to flap in the breeze), the greater the force ‘f’, and the faster the boat can potentially go.

The fin acts in a similar fashion to the tires on a car. They both minimize sideways movement and allow easy forward movement. For example, if you push a car on an angle, it will resist moving diagonally, and instead will only move in a forward direction.

Diagonal force pushing a car forwards

Diagonal force pushing a car forwards

For this reason, the fin should be all the way down to minimize sideways slippage.

For more tips on how to get more out of your upwind sailing, check out this video with self-coaching tips from British Sailor Penny Clark who competed in the 2008 Summer Olympics…

https://www.youtube.com/watch?v=ulXTIOiNJ40

 

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6 Comments

  1. Craig Tidball on June 7, 2014 at 9:10 pm

    I’m a newbie and having trouble with the paragraph under the diagram regarding forces on a boat. It may be a matter of terms but seems to me that when you “let the sail out” (to the point it flaps in the breeze) that you would not go faster but slower. When you let the sail out aren’t you causing it to not “harvest the wind”? Can you get me on the right track here?

    • admin on June 9, 2014 at 5:58 pm

      Hi Craig
      Thanks for your question.
      In relation to where it says “let the sail out”, I am just trying to point out that the more hard on the wind or upwind you are sailing, the less forward force you have propelling you forward. As you bare away (and “let the sail out”), you increase the force forward and can potentially go faster.
      It’s a little difficult to explain. I have changed the wording on the site slightly to try and make it a bit clearer.
      Hope that helps.
      cheers
      Brendan

      • James on August 27, 2016 at 6:21 am

        When I beat upwind in my laser radial, I consistently cannot point as high as other lasers. Centreboard is down. Mainsheet in. My kicker is tight, outhaul too. Why can I not point as high?

        • Admin on September 6, 2016 at 5:07 pm

          Hi James
          Thanks for your question. There are quite a few things that can affect the upwind sailing angle on your laser.
          It may be that you are overpowered, so have to ease the traveler, which can affect your hight.
          You didn’t mention the cunningham. You may need to pull it on a bit to flatten out the sail. But don’t use too much.
          Another thought may be that, since you say that you can’t point as high as others, this may not be a bad thing. If they are all overpowered, and heeling more, they will naturally point higher, but since they are not keeping the boat flat, they will also be sailing slower. When you heel the boat, you will point higher, but to keep the boat from rounding up, you have to pull away, which adds drag and slows down the boat. Keeping the boat flat is best.
          Another reason why you may not be pointing as high is because you may be in dirty air. This disturbed air approaches at a slightly worse angle, meaning you won’t be able to point your laser as high.
          If you have an old sail, it may just be that it sags and you can’t get the best shape out of it to point well.
          If all else fails, have a chat with some of the folks that you know can sail at a higher angle than you and compare settings, and even have a match race (while not racing) to see exactly how they have their sails set and to compare angles.
          Hope that help a little.
          cheers
          Brendan

  2. Dave on July 16, 2017 at 7:50 pm

    I sailed for years without really understanding this. Thanks for doing this website, it’s getting clearer now…do you have to have the boat at 45 degress to the wind and then adjust the sail angle? Does it depend which direction you want to go in the first place? Should I read a lot of books until the penny drops and then go out and practice by myself until it becomes instinctive?

    • Admin on July 17, 2017 at 11:20 am

      Hi Dave
      Thanks for your comments and I am glad that you have found the website useful.
      When sailing upwind, you should be able to point higher than 45°. However, if you are sailing at 45° (which I would call a reach), you can start to bring the boat up into the wind more, and as you are doing this, pull on the mainsheet at the same time. If you have the mainsail fully on, and the sail starts to depower or it starts to luff (where the front of the sail loses shape because it is not catching any wind), then come away a little until the sail fills.
      If the wind is consistent, and depending on your ability, you may be able to try to have the mainsail fully on, and then instead of adjusting the sail angle by letting the sail in and out, you adjust the boat angle by steering with the tiller and your body weight to keep the optimum angle to the breeze. You want to try to keep the telltales flowing.
      I’m not sure what you mean by “Does it depend which direction you want to go in the first place.” When you are racing, you want to try to sail in wind that is not disturbed by other boats that are around you (generally upwind of you – you do not want to be in their disturbed air). Another thing to consider is that the wind is always swinging – sometimes not be much (maybe by ~5°), other times it swings a lot (eg. 30° or more). If you are sailing to an upwind mark, and the wind swings so that it points your dinghy away from the mark (called a “knock”), then it is often a good idea to tack (the other tack will lift you up to the mark. This is called a “lift”). This minimizes the distance you have to sail. You want to try to sail as many lifts as possible to take advantage of sailing the minimum distance around the course.
      It’s always a good idea to read up and talk to people to try to increase your understanding as much as possible. However, there are a lot of people with different opinions, so it’s always good to take that information and to try it out for yourself and build your own opinions of what works and what doesn’t. Nothing beats experience on the water – you can read as much as you like, but without real experience on the water sailing, it won’t become instinctive and you won’t learn the feel of the boat, the wind, and the water.
      Well done on wanting to learn more. Hope this helps a little.
      All the best
      Brendan

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