Windward heel

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

  1. Deimos

    Deimos Member

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    However, assuming the wind is parallel to the surface of the water, the more heel (to windward or leeward), then the lower the effective surface area of the sail with regard to the wind. I think of it as max surface are of sail when boat upright, heel at 45 degrees and you lose a lot of the surface area from the perspective of the wind. You may start lifting the hull (don't know) but you will then be doing it with an effectively smaller sail (smaller to lift you and smaller to drive you).

    I would think that windward heel beneficial effects must be something to do with balancing the boat and the underwater shape rather that starting to lift the hull. If this is true then it does not necessarily mean that more is better.

    Ian
     
  2. glasky

    glasky Member

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    Glenn Bourke (3 times world champion) , in 'Championship Laser Racing', 1993, Furnhurst Books is also an advocate of 'windward heel' upwind in 'light-air'. Pictures p45 & p62 suggest however that conditions when this is applicable are certainly above that of a 'drift' but before you are two blocked (photos show blocks about 2-4 inches separated) and hiking still possible with toes under the grab rail.

    Seems to work (give good height) - on relatively flat water and relatively smooth (cooler) wind - and if your concentation holds enough so you can steer essentially with boat trim. Much harder to sustain in blusterly conditions.

    Bourke indicates he is not sure whether it is extra hydrodynamic efficiency of the foils or enhanced sail-plan angle of attack effect - but it seems to work if you can get the balance and steer by tourkeing and balancing the hull.

    Anyone know why suggestions abound that a Radial should be heeled to leeward up to 10 degrees upwind? Is it just a 'feel' thing to get back more of the traditional Laser weather helm?- have noticed also that most top Radial sailors sail very low in the groove (sometimes footing at angles that appear almost rediculously deep to a standard sail sailor in chop) but get speed and then wind up to windward.
     
  3. computeroman2

    computeroman2 Member

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    I think the angle of attack theory has some good chances. The I14's are experimenting with gybing centerboards, and the Tasar has had them (right?) since the boat was released. It probably doesn't work in heavier winds because more apparent sail area is more of a gain than a higher angle.
     
  4. glasky

    glasky Member

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    Pugwash,

    I too am a keen Windsurfer, but the pictures in Glen Bourke's book from astern when he is sailing with windward heel show a virtually vertical leech (i.e. the windward heel is just sufficient so that the leeward bend of the loaded mast is negated and the trailing edges of the sail are now pretty much vertical instead of off to leeward as they would be if the boat was flat.

    Despite the theoretical advantages of lift/lightening of the Windsurfer rig as it is inclined over the sailor to windward most racers seek to keep the rig as vertical as possible (some using extra wide booms to do this together with down pulling seat harness that vangs the sail) to increase mast-step pressure. Maybe this is because of the differential in hydraulic lift available from the water compared to that available from air and a need to get fin - if not centreboard these days - foiling hard to maintain height)

    The comments by others about sitting forward and an initial lee (possitive) helm suggest we are talking about both angle of attack of sailplan and flow around the foils. Maybe we are in effect getting a 'gybing centerboard' action and enhanced roll-over vorticey effects from the rig - the noticeable cut-out when waves or other disturbance occours suggests this kind of interaction - a bit like the transition from extreme windward railing by the lee down wind performance (or flying a hull in a catamaran downwind) and the pause/helm changes if you inadvertantly drop flat again and resume stalled luff to leech flow.

    Would be good to get a Bethwaite comment on this.
     
  5. cabalar

    cabalar New Member

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    I've measured the same upwind course between 2 buoys comparing leeward vs windward heel in stable light wind conditions. With windward heel it seemed to take around 20% less, partly because of speed, partly because I could tack much more near the buoy.

    I've also used it in a recent regatta with light wind and have no doubts now: it is clearly better. I gained a lot of advantage in each upwind leg.

    One "effect" I felt is that from time to time I didn't feel any pressure in the main sheet, so it seemed that the sail was just "sheeted" by the boom weight.
     
  6. Combatsailor

    Combatsailor New Member

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    You first have to get your boathandling down and then worry the fine points. Race a lot and find a training partner to check yourself. Go upwind/downwind in all conditions to get your boat handling down. Make yourself go out in a blow and just do upwind/downwind...it's the best way to master the Laser. Sail other classes. Particularly small tubby boats like Tech Dinghys and Interclubs. You sail them fast downwind with a lot of windward heel and, the Techs are so tippy that you will soon learn when you're in the groove. Don't get too technical and worry about the theories until you're fast/undercontrol downwind in a blow and in light air. Then you can break it down and find that 1/10 knot you need to move to the next level.
     
  7. computeroman2

    computeroman2 Member

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    combatsailor- Um....Thanks, but that's not really what we're looking for. There are some of us here that are looking for that 1/10 knot. Furthermore, the estimated 20% decrease in a timed run is really significant. In a close fleet, 20% could be the difference between first and last.

    There's a good discussion about this with boats in general on Sailing Anarchy: http://www.sailinganarchy.com/forums/index.php?showtopic=45481
    the thread basically divides it into a bunch of issues- not the rudder, possibly hull dynamics, as well as some rigs just doing better when cranked to windward.
     
  8. knot_moving

    knot_moving Member

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    Doesn't seem to work well with waves. We were sailing in pretty light winds Sunday - maybe 5-8 kts. Didn't seem to ever have to hike out very hard. But there were waves from the earlier 15kt winds.
    Windward heel didn't seem to help me point any higher in these conditions and I seemed to maybe even lose a little boatspeed.
     
  9. Yiannis

    Yiannis New Member

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    Hi chaps,

    having watched Steve Cockerill's DVD quite a few times I can tell you that he doesn't explain things very well. As you are about to understand what he is trying to say, he will say something lese that will confuse you completely. Sometimes you need to pause the DVD and think what he said.

    Anyway, I will try to explain how me and a couple of guys understood it.

    Heeling to windward will make the boat bear away (leeward). So, you turn your rudder to leeward to counter act the "turning". Somehow the heeled hull and the rudderblade get into a balanced state so the tiller is light. You don't feel any resistance on it. This means that the rudder blade goes straight and acts as the centreboard. The boats centreline is not pointing to the direction you are going but slightly to windward. This means that your centreboard is pointing to windward. So water is "hitting" your centreboard from the leeward side (more presure) while it creates a point of lower pressure on the windward side. This pushes your centreboard and consequently the boat to windward.

    He says that it's quite tricky to get the balance right and I have to admit that although I have tried to do it, I haven't succeeded. On the other hand I have been sailing only for 9 months (so I am still a newborn when it comes to sailing) and I lack experience. I need to improve my boat handling, before I get to this level.
     
  10. cabalar

    cabalar New Member

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    Mmmm, I think that this is not a particular feature of being heeled to windward. In fact, as explained in "The Physics of Sailing" (by Bryon Anderson: it includes a nice diagram of water flow) the centreboard always works like that in an upwind course. That is, the bow points slightly to windward w.r.t the real direction (that is, your boat is slightly shifted sideways to leeward). This means that a centreboard has an angle of attack causing a lift force to windward.

    But perhaps the keypoint has to do with the rudder. As you point out, heeling to windward makes the boat to bear off and causes an initial lee-helm. In principle, this is bad, as heading up with the rudder would act as a brake. But curiously, after a while, once you get a bit of speed, the tension in the rudder disappears. It may be the case that the angle of attack of the rudder in that position creates a lift force to leeward (and a bit upwards) in the rear part of the boat, which together with the centreboard lifting to windward, makes a pair of forces helping to point higher.

    In my experience it seems that the whole effect is a bit sensitive and a kind of forces balance must be reached. I've also experienced that waves destroy the effect, what I think supports this hypothesis based on lift forces on foils.

    Pedro.
     
  11. cbyc_radial_sailor

    cbyc_radial_sailor New Member

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    I heard somewhere that in an optimist, 15 degrees of heel downwind is optimal. I am not sure about the lasers, but I am sure it is around that.
     
  12. Roadie

    Roadie Member

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    I have seen the DVD and the wind is strong enough to hold the boom up. The wind is 'light' by our hardcore standards but its not really that light in reality. It works well, I have tried it but it doesn't really work in wind that is lighter than would allow to be just about hiking. It relies on good flow over the foils so you can get extra lift if you stick at it for a while, it's not going to work if there's no decent flow over the foils.
     
  13. oztayls

    oztayls Member

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    I too have experienced the added lift from heeling the Laser to windward going upwind in a light breeze and flat water. The tiller is definitely off centre and to leeward and vibrates slightly. What I think is happening is that heeling to windward increases the angle of attack of the main foil, ie. the daggerboard. The Laser has a very fat daggerboard and a long chord which is lengthened further because it is raked backward quite a long way. Aerodynamicists will know that a fat wing, ie. one with a large thickness to chord ratio, can still allow flow to be attached on the suction side at larger angles of attack than thin foils. (The downside is higher drag, but as the Laser is a "slow" boat, the foil is one of the thicker kinds, probably a NACA 0012 or maybe even up to 0015. I have not measured it, but it's fat!)

    When sailing flat, the Laser's normal angle of attack for the daggerboard is about 2.5-3.0 degrees due to the normal leeway. (All sailboats have a certain amount of leeway when sailing upwind. Skiffs that plane upwind make much less leeway than a Laser) At normal leeway, the Laser's rudder is therefore not in the path of the daggerboard's turbulence. However, when heeled to windward and with the dagger foil at an increased angle of attack of probably 3.5-4.0 degrees, the rudder foil comes into the path of the daggerboard's turbulence. When this happens, the flow over the rudder is more turbulent and it loses lift. This turbulence and decrease in rudder lift might explain the vibration we feel and the phenomenon where the rudder is pointed to the leeward side (the tiller is 2-3cm past the centreline on the leeward side) while the boat is tracking straight. In a stronger breeze and with faster boat speed, this situation would be a real performance killer, but while in this "groove" the Laser can live with reduced rudder efficiency and exhibit this quirk and "climb" to windward from the enormous lift generated by its enormous dagger foil.

    Well, that's what I think is happening anyway...;)
     
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  14. Roadie

    Roadie Member

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