Windward heel

[chrisfsi]

Here's a question for all you engineers out there (or anyone else for that matter..). On the one hand we're told "flat is fast" - make best use of the aerodynamically (should be aquadynamically:confused: ?) efficient shape of the hull.
On the other hand, when sailing downwind in light airs, then pronounced windward heel ("reduce the wetted area") seems to be more effective. What determines the point in sailing downwind where the windward heel becomes more effective than sailing flat? Presumably when the drag effect of a flat hull (with large surface area in contact with the water) is greater than the drag effect with a reduced surface area in contact. But is this point measurable?

Also, if this works downwind, would it not in theory also work upwind? Although balancing the boat might also be next to impossible. Anyone ever tried it??

[mlemieux1978]

the main advantage to windward heel downwind is that it brings the center of effort of the sail (approx. center of the sail's area) over the boat's center of gravity (which is the centerline of the boat). this makes the sail's horsepower drive the boat in a balanced (sort of) way, with less helm input needed and the added benefit of less wetted surface.

the importance of sailing perfectly flat uphill stems from the foils. the foils which generate the lift which keeps the going upwind and not stalled sideways, operate best when the boat is flat. This is also key to the rudder's performance, because when the boat's flat, less helm input is required. Leward heel will generate weather helm, which will require you to correct, bringing the tiller "up" toward you, which you have no doubt experienced, creating drag. conversely, windward heel will generate lee helm, which does the same thing except it also makes the rudder "stall", which is even slower because the rudder is not providing lift. tink of this like the flaps on an airplane wing.

check out ed baird's book on laser sailing for the basics of this with illustrations. then try sailing without the rudder installed on a light air day as the book describes. when you can master this, your light air sailing will improve by leaps and bounds and you will be able to help steer the boat around marks with your weight placement instead of large rudder inputs.

hope this helps

[sailor327]

yeah also windward heel downwind gets the most sail area up higher where the better wind is as possible. And when it comes to going upwind, being flat also elps you track to windward better and nutralizes the helm.

[chrisfsi]

Thanks - I didn't realise the wetted area / drag issue was such a small part of the picture. I've never had the nerve to try rudderless sailing, I really must make the effort to give this a go..

[WestCoast]

in the Rooster DVD, there is one guy they show who heals to weather slightly in light/light-moderate breeze. Points the same, but it sure seems from the video that he is gaining height on the guys sailing flat.

Could be a million other things going on, but they point it out in the video.

I've tried it a few times, it's very hard to find a groove *shrug*

[chrisfsi]

This weekend past was the first time I managed to get the windward heel / by-the-lee combo working downwind, which was a great feeling; guess I'll have to focus on getting that perfected first..!

[computeroman2]

Another factor to consider is gravity. Upwind, heeling slightly to leeward allows the sail to naturally fall into its shape as opposed to strait down, which in turn puts less of the sailforce to work holding out the sail and more to driving the sail. The same thing happens when you're by the lee and heeled to windward off the wind- the heel keeps the sail out and filled.

[Georg W.F.]

I think we are talking about windward heel, not leeward heel. Nevertheless I agree with your point and in really light air this constitutes a problem for windward heel, I think.
I do not have this dvd, but how much heel are we talking about? I assume very little, since otherwise gravity would indeed pull the sail and boom to windward.
Georg

[mlemieux1978]

It has been my experience that a slight windward heel upwind is effective immediately after the start when you are trying to pinch off the guy immediately upwind of you. Never tried to sail slightly heeled to windward for a whole beat though. What part of the race does this footage appear to be from?

[RobKoci]

I for one am totally sold on windward heel to weather in light wind. You get height like you wouldn't believe. It's freaky. I sure hope everyone else gives up on it, 'cause it kicks.

I rounded 2nd at the first top mark in light air at the Masters Mids East last year because of it. No doubt in my mind you got to do it in light air. There is nothing faster. We had light wind in Toronto all summer and me an one other guy got the hang of it. In light air, we were very fast.

Going the right way in light air. Now that's another thing.

[rtdanforth]

When heeling to windward (beating, in light air), how do you avoid having the boom fall over to the windward side? It seems as though gravity would prevent the boom and sail from staying in the normal, leeward position.

[cabalar]

I for one am totally sold on windward heel to weather in light wind. You get height like you wouldn't believe. It's freaky. I sure hope everyone else gives up on it, 'cause it kicks.


That looks promising. I usually have big problems to point high when going upwind in light air (probably due to my weight). However, I have the same doubt raised by Georg (sorry, I don't have Rooster DVD) for heeling the boat to windward in those conditions:

wouldn't the boom fall down to windward, positioning the sail in a wrong way with respect to the wind?

Or is it perhaps that you manage to hold the boom "up" with your hand at the same time?

If this is the case, I guess that you must be in an extremely uncomfortable position, although I wouldn't worry about it if you really gain some height!

Pedro.

[TimClark]

You don't heel the boat to weather to the point at which the boom would fall over to windward. You have a small amount of heel, not even enough to have the windward rail in the water(too much wetted surface area), I have gotten it to work only a few times, its really tricky. Once you finally do it, you will know its happening.

[Owyn in Barnsley]

You don't do it when it's that light! I've seen the video and had some trouble getting my head round why it occurs, I don't think Steve's explanation is quite right. I'm doing engineering at uni at the mo, I think there is every chance it has nothing to do with hydrodynamics and something to do with the rig. the only way you can get more lift off the foils is to increase their angle of attack, this would require pointing higher while making leeway (which wouldn't happen, the lift stops leeway) also something would have to happen with the rig to enable it to point higher. So I'm not sure why it happens but I know that it does, it could just be that keeping the boat uber flat is where it is at.

[mlemieux1978]

Everyone keeps talking about wetted surface. the volume of the boat that is submerged is not going to change as a basic rule of bouyancy. It stands to reason that the wetted surface may actually be more since to stay afloat, the hull will actually be drawing more when you heel it over.

as far as the phenomena being a function of the rig, I believe its because of the unstayed mast. Like a freedom unstayed rig, the top of the mast will naturally fall off to leeward. Maybe heeling to windward counteracts that while going upwind and makes it more efficient.

[Owyn in Barnsley]

I was thinking it could be about getting the tip of the mast further over to the centreline of the boat, not over the side deck like if the boats flat.

As far as wetted area goes, total drag is made up of a combination of viscous and inertial forces, i.e. the stickiness of the water and water being moved out of the way (also lower pressure behind a body, doesn't really happen if you don't keep dunking the transom)

At lower speeds skin friction dominates which is why it is good to sink the front end in light winds (you get a lower area to volume ratio in the water) at higher speeds the inertial forces dominate, hence you try and get the boat to move less water by sitting it on top of it (planing)

[chrisfsi]

Ah-ha - I thought there had to be an engineering answer! Viscous and inertial forces was clearly what I was thinking off;) .... Now I know the real answer is get out and sail more, and it will all come naturally, but as I'm stuck in the office at the moment, I'm kind of interested if the point at which inertial forces start having greater effect than viscous forces (ie, when flat starts getting more effective than heel, if I'm understanding this right..) is determinable? Or am I just getting TOO nerdy???

Windward heel at the start of the beat in light winds sounds very interesting - sorry Rob, you may have let the cat out of the bag! Now you'll see hordes of boats at the weekend desperately trying this out, and all the non-TLF sailers wondering just what the heck is going on!

And it's HYDRO-dynamics, not aqua-dynamics - think I'm getting my Greek and Latin roots mixed up - silly me - happens all the time... :D

[Owyn in Barnsley]

Well if you really must know, the flow transition from laminar to turbulent occurs at a Reynolds number of around 2000, a little bit less than this is where the inertial forces start to dominate. but in reality I get rid of windward heel on the run when it all starts getting a bit lairy, even then I'd use a bit to try and neutralise the helm, all depends on how big your cobblers are!

[chrisfsi]

Thanks - of course, Reynolds 2000, how could I have forgotten..........:eek:

Think it's time I got back to seat-of-the-pants stuff and just practiced more! But will definitely try a bit of windward heel at the start to see what effect it has...

[Merrily]

all depends on how big your cobblers are!

What are cobblers? Just a gut instinct that I don't have any. :rolleyes:

[Owyn in Barnsley]

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!

[Kevin Pierce]

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

[computeroman2]

Everyone keeps talking about wetted surface. the volume of the boat that is submerged is not going to change as a basic rule of bouyancy. It stands to reason that the wetted surface may actually be more since to stay afloat, the hull will actually be drawing more when you heel it over.

as far as the phenomena being a function of the rig, I believe its because of the unstayed mast. Like a freedom unstayed rig, the top of the mast will naturally fall off to leeward. Maybe heeling to windward counteracts that while going upwind and makes it more efficient.


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.

[RobKoci]

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?

[chrisfsi]

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...:(