Heeling Explained
- Thread starter Don Guillette
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I am not a mechanical engineer, but I have always assumed that the air foil effect happens with air which expands and therefore creat a lower pressure when flowing over the air foil.
With water being incompressible and stay as liquid until cavitation occurs, is the air foil affect still there?
Can some one please confirm or correct me on the basic assumptions for the Bernulli effect?
With the keel having a symmetrical shape on both sides, there is no uneven lift when vertical but may have a lift due to angle of attack when heeling. If so, the lift is actually in the same orientation as the heeling moment created by the sail.
The main drag has to come from the rudder though for doing all the work in offsetting weather helm.
Oliver.
With water being incompressible and stay as liquid until cavitation occurs, is the air foil affect still there?
Can some one please confirm or correct me on the basic assumptions for the Bernulli effect?
With the keel having a symmetrical shape on both sides, there is no uneven lift when vertical but may have a lift due to angle of attack when heeling. If so, the lift is actually in the same orientation as the heeling moment created by the sail.
The main drag has to come from the rudder though for doing all the work in offsetting weather helm.
Oliver.
This is incorrect. Lower pressure is generated by conservation of mass, energy and momentum as the path of air and/or water is curved around the foil. This is desribed by the Euler equations outlined previously in the thread.
Yes, the lift generated does not require the fluid to be compressible. Therefore the foil effect is still present for incompressible fluids such as water.
Although the Bernoulli equation is widely believed to govern the generation of lift, it in fact does not. It describes the change in pressure along a streamline (that is, along the direction of flow) not perpendicular to it. Therefore it can not describe lift, since lift is generated in a direction perpendicular to flow. The Euler equations outlined previously describe the change in pressure across (perpendicular) to a streamline. The Bernoulli equation does in fact describe the operation of pitot tubes in aircraft. Note that pitot tubes are oriented along the streamline (that is, in the directino of flow).
The angle of attack is generated by leeway in the boat. The rudder (assuming a couple of degrees of weather helm) also generates an airfoil effect in the opposite direction of heeling. Up to a point, both of these will counteract heeling. However with enough leeway the keel can actually serve to trip up the boat and increase heeling. In high winds, I can reduce the heel angle on my boat by pulling up the centerboard. (My boat has a shoal keel/centerboard arrangement, so my centerboard is not weighted and pulling it up does not negatively affect stability). When I do this, the boat sits more upright, but I pick up a bit of leeway.
A few degrees of weather helm actually helps the keel function as an airfoil. Beyond a few degrees it will stall out and become a major source of drag.
Hope this helps!
Entirely WRONG, and was the core of the Wright Brothers early experiments and was documented (I believe) within their patent application.
1. If the air stream 'speeded up' on the leeside and yet both 'particles' arrived at the 'same time' it would only because that the air is 'compressible' ... and for the sake of aerodynamics at normal atmosphere pressures and less than supersonic speed, air in accordance to aerodynamics is essentially INCOMPRESSIBLE. At atmospheric pressure, the leeside flow arrives at the leech LATER than the 'windward side' becauae there is MUCH MORE flow on the leeside.
1a. The confusion is what one 'senses' when near a foil that is operating is because on the WINDWARD side of the foil there is a '(vector) component' of the air flow that's GOING FORWARD along the windward side which causes the upwash way out in front of the sail/foil, and there is MORE 'rearward' flowing air on the leeside .... because the relative motion of the windward side of the wing/foil is moving forward ... and is 'pushing' air forward. Way out in front of the oncoming boat/sails,etc., the air then 'gets out of the way of the oncoming' windward side and FORWARD (vector component) windward flow and crosses the 'stagnation point' to the LEESIDE. Because one automatically senses the sum reduction of flow (forward motion or air subtracted from the rearward motion along the windward side one 'perceives' or 'senses' that the leeside flow is somehow 'faster' and the windwards side 'slower' ... but it really isnt FASTER or slower, there is just MORE (amount) flowing on or TO the leewards side, AND the leeside flow 'may' arrive at the 'leech' much later than the vectorial result of the windward side flow !!!!!!!!!
All that is necessary for 'aerodynamic flow' is that
A. the speed of leeside flow is equal to the speed of the windward side flow AS it EXITS the sail/foil at the leech - called "kuta condition" (consider this to be the FIRST LAW of aerodynamics of wings/sails) ---- get those leech tales flowing 'straight back'!!!!!!!;
B. that there is an 'upwash' (air getting out of the way, waaaaay out in front of the oncoming windward side).
C. the flow across the sail(s) is attached, not separating nor developing 'destructive turbulence'.
D. there is a quite large 'rotor' or circulating vortex of air (starting vortice) 'following' the foil/sail/wing (balancing the 'upwash' that is waaaay out in front of the foil).
E. A sail generates 'lift' ONLY because the air has 'viscosity' (direct energy 'transfer' -by friction- of the winds motion TO the sail/wing/foil), no viscosity or 'fluid friction', NO 'lift' - simple!!!!!!
The Wright Brothers had is Correct ....... and MILLIONS of high school 'science' teachers have had it WRONG since the time of the Wright Brothers (USA is more than 50th out of 196 nations in world ranking of math and science of its highschool students - VERY strong HINT here).
Question? If the USA highschool science class 'stuff' was correct .... wouldnt one expect the flow through the 'slot' between jib and main to be at a higher velocity than the flow on the leeside of the jib and weather side of the main? ..... Actually, The flow in the 'slot' is SLOWER (sometimes approaching ZERO flow velocity) because the forward flow on the WINDWARD side of the jib is CANCELLING the aft flow on the leeward side of the main ..... dont believe it, then take your hand held anemometer and measure it !!!!!!!!! record your observations, then deduct the speed of the boat ---- windward side flow has a FORWARD flowing component .... the air is CIRCULATING around the sail(s)!!!!!!!!
The total vectorial sum of 'aerodynamic' air flow is 2 parts:
A. a vectorial CIRCULATION of air flow AROUND (forward flow on the windward side and aft flow on the leewards side of a sail/wing/foil, ..... one can SEE the windward forward flow during 'light to moderate wind' condtions when the sails camber (outhaul) is perfectly set for maximum boat speed output of the sail ..... simply by watching the windward side tell tales pointing FORWARD!!!!! .... Plus,
B. the velocity of 'oncoming wind' MINUS the velocity of sail/boat going forward.
HEELING. not destructive to forward speed of a boat until approx. ~25-30° of heel on 'normal' hulls when skin friction, and sideways 'slip' begins to predominate. Heeling is merely a REACTION of the power of the wind being transferred to the sail in direct opposition to the mass of the 'balast' and 'form stability' of the hull ---- the resultant HEEL is an EQUILBRIUM between the force on the sails and the 'restorative forces': mass of keel plus form stability . Heeling is nothing more than the BALANCE of wind strength (a moment arm or Force times distance) through the 'centroid' (combined CE of the sail plan) .... versus .... the righting forces from the keel mass and/or the form stability of the hull (a moment arm of force times distance).
ADVANTAGES of Heeling:
1. longer waterline length on some hulls ('rule beaters' with larger 'overhangs') - the waterline length get loooonger the further the boat heels over.
2. larger Lateral Resistance (due to deeper immersed hull side)
3. Less 'skin friction' .... broad ultra-beamy boats that have the least amount of wetted surface area when heeled -- ie.: scows or the modern 'fat assed' or wide-sterned, 'triangular' hull form with flat bottoms aft ... race horses that can perform exceptionally well at ~ 30° (or less) apparent.
4. 'lift' from the curved hull 'side' that is immersed, the other side 'dry' .... again broad beamy boats or planing hull 'skimming dishes'.
..... usually, a well designed boat from a top-notch designer can heel over without much 'penalty' .... TO ITS RAIL in the water; and/or, the boat begins to develop noticeable 'adverse helm' pressure (because the relationship between CE and CLR and/or begins to 'slip' to leeward becomes 'out of balance').
Ignoring the 'pucker factor' of the helmsman, the REAL sign that one is heeled over too far is ADVERSE HELM PRESSURE, or the 'velocity made good' (VMG) begins rapidly 'fall off'. VMG is the 'key' to how far a boat should heel .... of course, if the boat develops a 'heavy helm' due to a large heel angle, the VMG will already be decreasing. The large side area of the 'topsides' that are immersed when heeled over are added to the 'lateral resistance' ..... dont be afraid of it, use it !!!!
;-)
So, as I noted to Don, in an e-mail that, yes, has a few typos, as one heels a boat, the otherwise symetrical foil becomes decidely asymetric. Please replicate the coffee and 3x5 card observations and tell me, is that not a change? Was the percent change significant?
Does anyone have access to a decent lab? I may know a 11th or 12th grade student wanting to do a science fair project on this.
Yes, if you heel too far, it is fun for the crew but sucks for racing. And as you heel too far, yes you disrupt the water flow too.
Does anyone have access to a decent lab? I may know a 11th or 12th grade student wanting to do a science fair project on this.
Yes, if you heel too far, it is fun for the crew but sucks for racing. And as you heel too far, yes you disrupt the water flow too.
I suppose that a neophyte sailor would comment on this thread at his peril. I seem to have joined it in the heat of the battle. Having flown one of my usual jets home from Calgary CA. today at 43000 feet, I proffer my opinion as both a sailor and a pro. pilot. We may argue the vagaries of heel till the proverbial cows come home, but the true argument is lift over drag. Rich H. and Joe seem to have represented the technical side of lift, but I am not sure that even Boeing has all the answers. The drag equation is the one that captures my spirit. While I will readily admit that I don't have all the technical answers, I will say that if the rudders boiling, you got a s%#t load of drag. So if you want to go to 43000, you can't tolerate a s%#t load of drag. These boats are all different and thus will yield a different optimal performance level. My boat (C320) likes 12 to 15 degrees of heel on a breezy day, but is a tender boat with a big rudder. Yours may be comfortable at 10 or 20. The point is a quiet rudder. I can't go to 43000 with the flaps out, and you can't go fast with a large heel and a boiling rudder. The boat will tell the discerning sailor what it wants and the reason or aerodynamics be damned. If you win you win. And if you think pilots are annal retentive, drink a couple of beers with an old sailor. And then go sail with him and pay attention. Thank you Don Guillette.
Okay..... let's settle this once and for all.... this article explains it all: http://www.gidb.itu.edu.tr/staff/insel/Publications/Cesme.PDF
Heh, heh............. well maybe not.
Heh, heh............. well maybe not.
If you had simply taken the time to read the entire thread before you posted that, you would have read my acknowledgment earlier to that fact, IE; pulsed smoke wind tunnel testing has proven that the air is separated at the trailing edge at higher angles of attack. However, this is fairly recent knowledge. A research paper from MIT is dated 2001. Unless someone had their nose deep in aeronautics the last 10 years they would have missed it, and most aviation mags still teach the misinformation. The Wright Brothers were certainly not aware of that fact in 1903, it took nearly 100 years to prove the theory false.
http://web.mit.edu/13.021/13021_2003/Lifting surfaces/lectureB.htm
However, that small factoid has absolutely nothing to do with calculating lift and drag of an airfoil or understanding how to fly a wing, and changes nothing with Reynolds numbers on NACA airfoils. The Wright Brothers calculations for lift and drag were so accurate that even with todays technology and computers we have only added a fraction of efficiency over their airfoil designs of both wing and propeller.
It also has nothing at all to do with how a boat sails, heels, or how an airplane flies. Drag is drag and lift is lift. Whether the molecules meet at the trailing edge of a foil or not is really only for technical discussion, nothing more. Bernoulli's laws still accurately predict wing lift and drag and the power needed.
Bentwing hits it out of the ballpark, in stating that a boiling rudder is the most indicative effect we can observe and control to reach greater hull speed.
So my take-away is that most of the discussion as it relates to foils, lift, heeling, and boat speed is essentially meaningless. Boat speed through the water isn't even going to be impacted by heeling (up to a point) except that heeling could increase the waterline length which would have some benefit. Think of it this way ... if heeling up to about 25 degrees actually maximized boat speed, then why wouldn't we set baggy sails so that we reached that degree of heel more readily? It's absurd, so we don't. We put on racing sails and trim them properly so that the boat sails on her feet and we maximize the force from the wind.
Rich put it best when he simply emphasized that there is no detriment to heeling up to about 25 d plus or minus. Heeling is just the balanced effect of the forces.
The separate discussion regarding lift and the positive affect to VMG is valid, I think, but not related to pure boat speed.
Rich put it best when he simply emphasized that there is no detriment to heeling up to about 25 d plus or minus. Heeling is just the balanced effect of the forces.
The separate discussion regarding lift and the positive affect to VMG is valid, I think, but not related to pure boat speed.
Lift over Drag
While the technocrats stack their pennies, those that can, do. During a 31 year career in aviation, I have been forced to absorb huge amounts of dribble in order to not miss the minutiae that keeps you from killing someone in an airplane. Lest you question why this applies to a boating thread, I might bring up the fact that a large amount of aviation fundamentals derive from maritime history. While Don readily concedes the floor to the high I.Q cannons, I on the other hand, take the tack that if you can't observe it, it don't matter. I appreciate the technical discussion as much as most, but I will also observe that this settles the argument until the next informed desk, bar, computer sailor writes a paper that settles the argument. If your goal is to go fast (a subjective term) in a sailboat, sheet the main, trim the jib, set the traveler. For heavens sakes reef if you must. The essence of sailing for me is pleasure and the technobabble will rarely get you to the windward mark first without a substantial amount of on the water knowledge. So go sail with someone who beat you last week. He might know a thing or two. Thank You Don.
Joe, you have a wicked side, don't you ...
Making us read that thing only to have 3 paragraphs in the conclusion which basically didn't say anything. I couldn't read it anyhow, so I scrolled to the conclusion.
Making us read that thing only to have 3 paragraphs in the conclusion which basically didn't say anything. I couldn't read it anyhow, so I scrolled to the conclusion.
i agree with TKANZLER,
i chartered a sun odyssay 40 once, and when the wind got stronger we heeled so that rail got in water, speed was 8kn (max i saw was 8.6kn tho it wasn't the gps... so wasn't the true speed). i reefed the jib 50%, significantly more comfortable heel, speed was still 7.5kn, let alone the significant force reduction on the rudder. if i knew how to trim it better maybe even could go faster with reefs.
i see the same effect on my hunter 28 but around 4-5kn range.
adding weight at the aft will help the keel do the lifting a little better i think. it all comes down to boat design and weight distribution.
boats with wings
http://www.dynamicstabilitysystems.com/
i chartered a sun odyssay 40 once, and when the wind got stronger we heeled so that rail got in water, speed was 8kn (max i saw was 8.6kn tho it wasn't the gps... so wasn't the true speed). i reefed the jib 50%, significantly more comfortable heel, speed was still 7.5kn, let alone the significant force reduction on the rudder. if i knew how to trim it better maybe even could go faster with reefs.
i see the same effect on my hunter 28 but around 4-5kn range.
adding weight at the aft will help the keel do the lifting a little better i think. it all comes down to boat design and weight distribution.
boats with wings
http://www.dynamicstabilitysystems.com/
Bentwing60: You're right I "have conceded the floor to the high IQ cannons". "A man has to know his limitations" and I can't go head to head scientifically with these guys because they'd catch me in 2 seconds but what I can do is sail a boat with the best of any sailor worldwide because sail trim is not that hard and there's only so much too it. It's like riding a bike -- once you learn how to ride how much more is there? I know what I'm looking for from a sail trim standpoint on any point of sail and wind condition. The main thing is I can feel the boat through my feet and the boat actually "talks to me".
Making us read that thing only to have 3 paragraphs in the conclusion which basically didn't say anything. I couldn't read it anyhow, so I scrolled to the conclusion.
Heh, heh.... scott..... I'm so happy you recognize the humor in it...... dense is not the word.... perhaps putting it in a nautical sense .... Joseph Conrad would have trouble with this piece.... and there are some items posted here that evoke the same character... god help us! Please don't try to explain how my cell phone works.... I don't care.....
Victory...
Basically, I like Joe's sense of humor. He posted that thing totally tongue-in-cheek.
Basically, I like Joe's sense of humor. He posted that thing totally tongue-in-cheek.
I was reviewing this thread and a couple of things struck me --- it was all the great info but the other thing was where do you guys come up with the "handles (CB Jargon)" you use? I like normal names like Scott, RichH, Alan, StuJ, Robert Lang and Joe"from San Diego". I especially like the name Joe from San Diego because that's what I call him!!!
The other thing was how many places on the internet can you get the sail trim detail info that folks on this forum generously provide? The answer is nowhere!!! If it wasn't for Phil & Bly at sailboatowners.com you'd be looking at a blank page right now. To show your gratitude - shop with them FIRSTinstead of BoatUS and WM.
Some day I'd love to meet the regular posters on this forum to share sailing stories and a few "Tinneys". Unfortunately I'd have to travel all over the US, Europe and my favorite places Australia and NZ.
The other thing was how many places on the internet can you get the sail trim detail info that folks on this forum generously provide? The answer is nowhere!!! If it wasn't for Phil & Bly at sailboatowners.com you'd be looking at a blank page right now. To show your gratitude - shop with them FIRSTinstead of BoatUS and WM.
Some day I'd love to meet the regular posters on this forum to share sailing stories and a few "Tinneys". Unfortunately I'd have to travel all over the US, Europe and my favorite places Australia and NZ.
Well put. I always have a few coldies available, so if you come by the DC area ever, let me know!
Dan
Don, the concession thing to the cannons comment was in no way meant as a slur. The truth is that the boats talk to all of us, only some have deaf feet!
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