Windward heel

Discussion in 'Laser Talk' started by chrisfsi, Nov 6, 2006.

  1. Owyn in Barnsley

    Owyn in Barnsley New Member

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    It must be an English term, they are what makes you uniquely male in the literal sense, although I have met a few ladies that have much bigger ones than some men I know!
     
  2. Kevin Pierce

    Kevin Pierce New Member

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    Great thread...

    Since the original post was about windward heel on the downwind leg, we should note that one benefit of doing so is that it moves the sail's center of effort (CE) so that it's above the hull, pushing the hull forward, instead of beside the hull, cranking the hull to weather. Too much windward heel (downwind) takes the sail's center of effort past the centerline of the hull and makes the boat go to leeward. Hence, the neutral helm when the windward heel is optimal.

    Kevin
     
  3. computeroman2

    computeroman2 Member

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    The volume will never change, but the ratio of volume to surface area can.
    For example, measure the S.A. of a 3-3-3 unit cube, then take the 27 units the cube was made of and make one line of them and recalculate S.A. The S.A. of the cube will be 54 units while the S.A. of the line will be 108 units. Same volume, different S.A.

    anywho, when the boat is heeled on its side or bow-down, the curve of the hull has the effect of creating a more cube-like shape as opposed to a flat shape- the curve allows the same hull volume to be immersed while there is less surface area compared to a flat hull.

    I'd be curious to know why the upwind windward heel thing works.
     
  4. RobKoci

    RobKoci New Member

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    The one thing that I use as an indication that I have the foils working right with windward, upwind heel is that the tiller is about 1" to 1 1/2" to lee of the boat's centreline with NO HELM PRESSURE. No helm pressure is really important. I can let the tiller go and the boat still tracks staight with the rudder in that position. It's kinda cool cause is shivers a little like you would imagine the fin of a fish but sticks to that general position. Is it possible (this question is directed at the engineers) that the tiller is acting like the flap at the back of a airplane wing relative to the board? Because that is certainly the position it takes. If that was the case, then the board and rudder would be creating a shape similar to the shape of the sail (concave on the windward side).

    Does this make any sense?
     
  5. chrisfsi

    chrisfsi New Member

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    Will leave the answer to the engineers, but it makes sense to me. FYI, was survival conditions on Saturday - at one stage I could only see the top 1/3 of the mast of the guy in front of me due to the swells - so definitely NOT a day to try the "windward heel on the start" trick.. Also last race of the season, so I guess this is one to try next year...:(
     
  6. knot_moving

    knot_moving Member

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    well i are a engineer but i always get my concaves and convexes mixed up!
    It sounds like (assuming again that this is in relatively light winds) your healing to windward upwind is changing the balance so that you don't have to use rudder to counteract the tendency of the boat to turn head to wind.
    Because the rudder is hinged at its front edge, if you were generating any force with it, then you would feel a force in the tiller. So if you are not feeling a force, then it is not generating a force.
    ???
     
  7. RobKoci

    RobKoci New Member

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    Ah. Very good point. So then, why is the boat tracking forward even though the tiller is in an attitude off the straight line. It must mean the boat is sliding to leeward, which would not be good (not to mention not make any sense since the effect seems to be to track the boat to windward). Could it mean that there is a hydrostatic pressure pushing the boat to windward (which is the other way of saying the boat is sliding to leeward).
     
  8. computeroman2

    computeroman2 Member

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    perhaps the windward heel changes the force alignment such that the CB is at an angle similar to when you're pinching but the sail isn't pinching.
     
  9. RobKoci

    RobKoci New Member

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    I'm pretty sure the reason for the excellent windward tracking is as the Rooster CD suggests; That the hydrostatic profile around the hull when heeled to windward results in the water passing around the hull on the windward side over a greater distance than over the leeward side, thus creating a lift toward the windward side. It is the same as the arodynamic principle that creates lift on the convex side of the sail or the top side of an airplane wing.
     
  10. cabalar

    cabalar New Member

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    I wouldn't be so sure about that supposed principle of the "greater distance". There seems to be no reason why air or water particles attacking a foil simultaneously should get to the same exit point at the same time. Have a look at:

    http://amasci.com/wing/airgif2.html

    especially at figure 2 from a windtunnel: you can see that particles going along the longest path actually arrive even sooner than the ones going along the shortest path.

    So, I would look for a different explanation...

    Pedro.
     
  11. RobKoci

    RobKoci New Member

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    Hmmm. Then where does lift come from?
     
  12. RobKoci

    RobKoci New Member

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    I just read this off the Rooster website:
    The Gybing centreboard Trick:
    If you can heel the boat to windward a few degrees, remembering to sit far forward, then use positive rudder to keep the boat on its normal course. At first this rudder feels like a push, but as soon as the board begins to generate lift then the rudder becomes light and neutral, but still over to the positive direction. Effectively the boat now follows a straight course, inline with the rudder in its positive direction. This means that the rest of the boat, including the board is now turned into the wind - effectively gybing to windward. Now every dog has its day, and this trick is very useful for extra height for squeezing a boat to windward and can be used for long periods if the boat speed does not drop. However, once there is a lull in the wind or a slowing wave, the effect can be catastrophic. Perhaps then the Chris Gowers' style would gain back some ground.

    This makes sense to me. This is exactly what it feels like when I'm hooked up and going fast with windward heel.

    But don't anyone try this!! It is very hard and you won't like it!! In fact, forget this thread ever existed. Carry on with your leeward heel upwind. Please!!

    RK
     
  13. cabalar

    cabalar New Member

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    Well, I'm not an engineer, so don't trust too much in my answer. I've read several explanations: some of them stress the angle of attack, other (from fluid mechanics) mainly talk about energy lost due to turbulences.

    As far as I could understand, the angle of attack is important: it creates a strait vacuum zone behind the foil that tends to be filled quickly. When the fluid tries to fill the vacuum, it accelerates. By Bernouilli principle, more speed in the fluid means less pressure (and vice versa) so the foil is lifted by a difference of pressure on both sides of the foil.

    The shape of the foil affects to formation of turbulences. In fact, flat foils work too, although not so efficiently. A curved foil helps the fluid to get "stuck" to its surface. Anyway, in the outgoing part of the foil there will always be a formation of turbulence: this cannot be avoided.

    The best explanations I could find where at this book:

    The physics of sailing. Bryan Anderson.

    It contains some graphics of pressure measures along a sail (upwind) that show that, in fact, the pressure in the winward side of the sail is lower than the lift experimented in the leeward side.

    But this is only what I understood from what I could read. Please, if anybody has a better or more scientifically founded explanation, tell us!

    Pedro.
     
  14. cabalar

    cabalar New Member

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  15. Merrily

    Merrily Administrator Staff Member

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    Rob, of course I won't try it. I hate trying difficult new things. ;) But I read that off Cockerill's website and never understood about positive rudder. Which way are you moving the tiller?
     
  16. 49208

    49208 Tentmaker

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    When you heel to windward, the hull's asymetric shape will want to head down, giving you lee helm (opposite of the normal windward helm when you heel to leeward) . So you end up pushing the tiller down to leeward to keep the boat tracking straight
     
  17. Owyn in Barnsley

    Owyn in Barnsley New Member

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    I think the whole thing is pretty complicated, there are some major 3d fluid dynamics occuring under the hull with the foils and stuff as well. It seems pretty obvious that heeling to windward works in some situations.

    The bit in the rooster vid where Steve suggests the under water shape of the hull is like a wing neglects the fact that the footprint is pretty shallow so the biggest flow is under the hull rather than round it.

    Any how, I'd like to see some investigation into it, but as the legendary Reeves and Mortimer said " I don't know how it works but it does"
     
  18. cabalar

    cabalar New Member

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    This weekend, during a small regatta, the wind became lighter for a while and I tried windward heeling for upwind. An objective fact is that I could point higher. This was not only my feeling, but I could observe it by a simple comparison to the rest of the fleet.

    As for the speed, I had the feeling that the boat was going faster as well, but I can't tell if this was something "real". I mean, I don't know what would have happened if I had made the usual slight heeling to leeward for light wind.

    Anyway, looking at the rest of boats, the possible speed difference doesn't seem so important in the tradeoff as the possibility of pointing higher. The latter was really significative. I ended first :) among a small fleet of 6, although the truth is that I was already going first when I tried this technique.

    Ah, and I experienced a clear lee-helm. Otherwise the boat naturally beared off.

    Pedro.
     
  19. Steve_Landeau

    Steve_Landeau New Member

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    Board lift is absolutely relative to angle of attack. Airplanes with symmetrical wings cannot stay in the air with an AOA of zero. Only aerobatic planes have this type of wing (so they can fly upside down easily, relate that to a sailboat tacking with both tacks being equal) and their nose will always be up slightly, even if you don't notice (sailboats leeway).
    No sailboat sails perfectly straight as long as they have only one board that is symmetrical. Boats with a symmetrical board/keel will have some amount of leeway. This is where your AOA comes from, thus creating lift, negative pressure on the high side...etc. Both hydro and aero - dynamics work in the same manner around an airfoil, so if you know it about air, you know it about water, and vice-versa.
     
  20. pugwash

    pugwash Member

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    My pet theory - When you windsurf upwind you lean the mast into the wind a portion of the drive created from the sail is forwards at some angle off the bow. A smaller but very interesting portion of the drive is upwards - lifting the board upwards through the mast step and through your footstraps - so the more you "windward heel" the more upwards lift you create, the less weight is on the water and the faster you go.

    Could something like this be happening when you windward heel a laser sailing upwind in addition to all the nice stuff going on underwater?
     

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