Windward heel

[knot_moving]

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?
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.
???

[RobKoci]

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).

[computeroman2]

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.

[RobKoci]

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.

[cabalar]

...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.

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.

[RobKoci]

Hmmm. Then where does lift come from?

[RobKoci]

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

[cabalar]

Hmmm. Then where does lift come from?

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.

[cabalar]

A remark about lift force (sorry, I know this should perhaps become a different thread): I've found a pair of good sites with lots of explanations and disregarding incorrect theories

http://en.wikipedia.org/wiki/Lift_force
http://www.av8n.com/how/

Pedro.

[Merrily]

I just read this off the Rooster website:
, 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.

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

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?

[49208]

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?

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

[Owyn in Barnsley]

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"

[cabalar]

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.

[Steve_Landeau]

Hmmm. Then where does lift come from?

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.

[pugwash]

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?

[Deimos]

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.


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

[glasky]

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.

[computeroman2]

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.

[glasky]

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.

[cabalar]

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.

[Combatsailor]

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.

[computeroman2]

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.

[knot_moving]

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.

[Yiannis]

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?

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.

[cabalar]

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.


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.