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How keel winglets really work
From: http://www.djaerotech.com/dj_askjd/d.../wingfin1.html
A finite span wing in upright flight has more pressure on the bottom of the wing than on top. Lift is always measured perpendicular to the local airflow direction, and drag is always parallel to it. Once you know these two bits of information, it's not hard to understand how winglets work. The higher pressure air under the wing wants to spill around the wingtip to try to fill in the low pressure area on top. This flow results in a tip vortex trailing aft from the wingtip, like a horizontal tornado. You can see these vortices at the wingtips of a jet fighter during a high lift maneuver in sufficiently humid air, or at the tips of an airliner's flaps during a landing approach in wet weather. The energy extracted continuously from the aircraft to make the air swirl like that is what we call induced drag. As you probably recall from our previous discussions of induced drag, it's at its worst when we're trying to make lots of lift with relatively little airflow. This means that slow flight (low speed, low mass flow, high lift coefficient) is one of the worst cases. This also means that the intensity of the tip vortices will be highest at these kinds of flight conditions. Now we need to talk about "helix angle". If you understand the pitch of a prop, you're already familiar with it. Helix angle is one way to measure how far something rotates compared to how far it travels forward in the same time. The blade angle of a propeller blade is nearly the same (minus its efficiency effects and local angle of attack) as its helix angle. A wingtip vortex has a helix angle as well. This angle will be nearly parallel to the airplane's direction of flight when induced drag is low, but twist up into increasingly greater angles relative to the flight direction as we slow down or pull more "G". If we have a significant amount of induced drag, and a correspondingly stronger tip vortex, then the flow at the wingtip will not be parallel to it, but rather at an inward angle on top and an outward angle on the bottom. This is where the winglets come in. If we park a lifting surface in the middle of this angled air flow, it will develop lift perpendicular to the angled air flow. The resulting lift will be angled forward, and the forward component of that lift will be producing thrust. The lifting surface (i.e.: "winglet") will also be producing drag of its own, including both parasite and induced drag. If the drag the winglet produces is less than the forward component of its lift, then there will be a net thrust applied from the winglet to the aircraft. This thrust actually represents some of the energy in the tip vortex, harvested from the vortex by the winglet and given back to the aircraft. That's it. That's all there is to it. It's so simple! OK, now the catch. How do we maximize that thrust? This is where it gets complicated. If you increase the angle of attack of the winglet by increasing the "toe-in" angle, then it makes more lift force (which should theoretically increase the forward component of that lift), but it also makes more drag force. Depending on the specific situation, this could increase, decrease, or not change the net thrust of the winglet. It's going to depend on a lot of factors, including the flight condition. This last item is particularly critical. Because the amount of induced drag, and the helix angle of the vortex decrease as you increase airspeed, the energy available for "harvesting" by the winglet decreases as you fly faster. Meanwhile, the parasite drag of the winglet is increasing. Eventually you get to a point where the total drag of the winglet is equal to the forward component of its lift, and at that point the winglet produces zero thrust. This is called the "crossover velocity". At airspeeds higher than the crossover velocity, the winglet adds to the aircraft's total drag, and you would be better off without it. Cheers |
How keel winglets really work
Navvie wrote:
From: http://www.djaerotech.com/dj_askjd/d.../wingfin1.html This is from a model airplane web site, and some of the terminology for hydrodynamics is rather different. For one thing, we don't talk about the "helix angle" of underwater foils. For another, attempting to get a net forward (or windward) lift component from keel winglets isn't going to work because they have to sail on both tacks. If an airplane were designed to spend 50% of it's time flying upside down, you'd see some very different wing section and winglet designs... in fact, you can look at some stunt plane designs and see... Fresh Breezes- Doug King |
How keel winglets really work
DSK wrote: Navvie wrote: From: http://www.djaerotech.com/dj_askjd/d.../wingfin1.html This is from a model airplane web site, and some of the terminology for hydrodynamics is rather different. For one thing, we don't talk about the "helix angle" of underwater foils. For another, attempting to get a net forward (or windward) lift component from keel winglets isn't going to work because they have to sail on both tacks. Yep, that's why they are on both sides. Cheers |
How keel winglets really work
.... attempting to get a net forward (or windward) lift component from keel winglets isn't going to work because they have to sail on both tacks. Nav wrote: Yep, that's why they are on both sides. So, are you saying that keel winglets *do* have a net windward lift, considered seperately from their contribution to the keel's lift? Fresh Breezes- Doug King |
How keel winglets really work
"Navvie" wrote in message ... From: http://www.djaerotech.com/dj_askjd/d.../wingfin1.html A finite span wing in upright flight has more pressure on the bottom of the wing than on top. Lift is always measured perpendicular to the local airflow direction, and drag is always parallel to it. Once you know these two bits of information, it's not hard to understand how winglets work. The higher pressure air under the wing wants to spill around the wingtip to try to fill in the low pressure area on top. This flow results in a tip vortex trailing aft from the wingtip, like a horizontal tornado. You can see these vortices at the wingtips of a jet fighter during a high lift maneuver in sufficiently humid air, How can you see this in New Zealand? They don't have any fighter aircraft. Plus you can see it in very dry air, like all the time at Davis AFB is Tuscon. or at the tips of an airliner's flaps during a landing approach in wet weather. The energy extracted continuously from the aircraft to make the air swirl like that is what we call induced drag. As you probably recall from our previous discussions of induced drag, it's at its worst when we're trying to make lots of lift with relatively little airflow. This means that slow flight (low speed, low mass flow, high lift coefficient) is one of the worst cases. This also means that the intensity of the tip vortices will be highest at these kinds of flight conditions. What happens when , at low airspeed, one injects air into the airflow? Now we need to talk about "helix angle". If you understand the pitch of a prop, you're already familiar with it. Helix angle is one way to measure how far something rotates compared to how far it travels forward in the same time. The blade angle of a propeller blade is nearly the same (minus its efficiency effects and local angle of attack) as its helix angle. A wingtip vortex has a helix angle as well. This angle will be nearly parallel to the airplane's direction of flight when induced drag is low, but twist up into increasingly greater angles relative to the flight direction as we slow down or pull more "G". If we have a significant amount of induced drag, and a correspondingly stronger tip vortex, then the flow at the wingtip will not be parallel to it, but rather at an inward angle on top and an outward angle on the bottom. This is where the winglets come in. If we park a lifting surface in the middle of this angled air flow, it will develop lift perpendicular to the angled air flow. The resulting lift will be angled forward, and the forward component of that lift will be producing thrust. The lifting surface (i.e.: "winglet") will also be producing drag of its own, including both parasite and induced drag. If the drag the winglet produces is less than the forward component of its lift, then there will be a net thrust applied from the winglet to the aircraft. This thrust actually represents some of the energy in the tip vortex, harvested from the vortex by the winglet and given back to the aircraft. That's it. That's all there is to it. It's so simple! OK, now the catch. How do we maximize that thrust? This is where it gets complicated. If you increase the angle of attack of the winglet by increasing the "toe-in" angle, then it makes more lift force (which should theoretically increase the forward component of that lift), but it also makes more drag force. Depending on the specific situation, this could increase, decrease, or not change the net thrust of the winglet. It's going to depend on a lot of factors, including the flight condition. This last item is particularly critical. Because the amount of induced drag, and the helix angle of the vortex decrease as you increase airspeed, the energy available for "harvesting" by the winglet decreases as you fly faster. Meanwhile, the parasite drag of the winglet is increasing. Eventually you get to a point where the total drag of the winglet is equal to the forward component of its lift, and at that point the winglet produces zero thrust. This is called the "crossover velocity". At airspeeds higher than the crossover velocity, the winglet adds to the aircraft's total drag, and you would be better off without it. Cheers |
How keel winglets really work
If set up with dihedral or when heeled, yes they can -but its small as
their area is small. Cheers DSK wrote: .... attempting to get a net forward (or windward) lift component from keel winglets isn't going to work because they have to sail on both tacks. Nav wrote: Yep, that's why they are on both sides. So, are you saying that keel winglets *do* have a net windward lift, considered seperately from their contribution to the keel's lift? Fresh Breezes- Doug King |
How keel winglets really work
Oz wrote: On Mon, 02 Feb 2004 11:27:49 +1300, Nav scribbled thusly: DSK wrote: Navvie wrote: From: http://www.djaerotech.com/dj_askjd/d.../wingfin1.html This is from a model airplane web site, and some of the terminology for hydrodynamics is rather different. For one thing, we don't talk about the "helix angle" of underwater foils. For another, attempting to get a net forward (or windward) lift component from keel winglets isn't going to work because they have to sail on both tacks. Yep, that's why they are on both sides. Cheers Which chucks you whole spiel out the window. Ever see a jet with winglets that extend to the lower side of the wing? Never flown inverted on a 747-400 no. Come to that I've never flown on any inverted jet, but if they were flying both sides up with equal frequency you can bet there would be winglets on top and bottom... It really isn't all about the end plate effect you know. Look at AC winglets -its all about controlling the parasitic drag from the keel tip. OK? Cheers |
How keel winglets really work
The Professor wrote: What happens when , at low airspeed, one injects air into the airflow? Depends on injection flow rate and position doesn't it? If it's a fart people may complain. Cheers |
How keel winglets really work
Nav wrote:
If set up with dihedral or when heeled, yes they can -but its small as their area is small. I'm not saying you're wrong, but the wing keel designers I've talked with have never mentioned it. First of all the winglet is mostly horizontal. Here is where Jax's favorite, the 'sine function' comes in... if the winglets produce a net lift, then it is going to be mostly up or down unless the dihedral and/or heel angle gets very large, like greater than 45 degrees. When you get done emailing Phil Bolger and the SAYRA race officials, you can email Evan Gatehouse, Stephen Baker, and Paul Kamen to ask them about it. They all hang out on other sailing forums and are quite knowledgable about this sort of thing. Of course, one of the most important functions of a wing keel, which you forgot to mention, is that it gets more ballast weight down low. A model airplane designer would not be concerned with that, though ;) Fresh Breezes- Doug King |
How keel winglets really work
Sorry,
But the wings are an AC keel are not intended to function of an aircraft winglet. The function of the aircraft application has been effectively described here, the the wings on a keel have a primary function that is different. The tip vortices are pretty much confounded buy the huge bulb (much like an aircraft tip tank will do). The wings are actually designed to provide additional lift to windward that is not dependent on the keel blade attack angle. That is why they pay so much attention to the attack angle of the wings during the set up and trials. They have to play out a dual between more angle for more lift to weather when heeled and less angle for less drag with the boat upright going to leeward. As the current IACC rules have not allowed this to be trimed underway, they only get to set it once per race, and if you listen to the discussions going on the background, you will here them talk about the adjustment as three-quarters or one-half degree. Matt Colie (certifications available on request) Nav wrote: Oz wrote: On Mon, 02 Feb 2004 11:27:49 +1300, Nav scribbled thusly: DSK wrote: Navvie wrote: From: http://www.djaerotech.com/dj_askjd/d.../wingfin1.html This is from a model airplane web site, and some of the terminology for hydrodynamics is rather different. For one thing, we don't talk about the "helix angle" of underwater foils. For another, attempting to get a net forward (or windward) lift component from keel winglets isn't going to work because they have to sail on both tacks. Yep, that's why they are on both sides. Cheers Which chucks you whole spiel out the window. Ever see a jet with winglets that extend to the lower side of the wing? Never flown inverted on a 747-400 no. Come to that I've never flown on any inverted jet, but if they were flying both sides up with equal frequency you can bet there would be winglets on top and bottom... It really isn't all about the end plate effect you know. Look at AC winglets -its all about controlling the parasitic drag from the keel tip. OK? Cheers |
How keel winglets really work
DSK wrote:
A model airplane designer would not be concerned with that, though ;) Now Doug, don't go making fun of model plane designers, remember "The Flight of the Phoenix", (Shute, IIRC). ;-) One case where the movie was just as good or better than the book, a rare event. Cheers Marty |
How keel winglets really work
One case where
the movie was just as good or better than the book, a rare event. ALL James Bond movies were better than ANY James Bond book. |
How keel winglets really work
Martin Baxter wrote:
Now Doug, don't go making fun of model plane designers, Sorry, I was not meaning to belittle any model airplane designers. Just pointing out that a wing keel for a sailboat fulfills a rather different function... several, actually! ... remember "The Flight of the Phoenix", (Shute, IIRC). ;-) One case where the movie was just as good or better than the book, a rare event. Never read the book, the movie was pretty good. We'll have to ask Peter W about which is better... Fresh Breezes- Doug King |
How keel winglets really work
DSK wrote: Nav wrote: If set up with dihedral or when heeled, yes they can -but its small as their area is small. I'm not saying you're wrong, but the wing keel designers I've talked with have never mentioned it. First of all the winglet is mostly horizontal. Here is where Jax's favorite, the 'sine function' comes in... if the winglets produce a net lift, then it is going to be mostly up or down unless the dihedral and/or heel angle gets very large, like greater than 45 degrees. Yes, that was my point. Did you see the dihedral on current IACC winglets? It's up to about 30 degrees (by eye). That neans when the heel is 30 degrees (a typical 'powered up' design heel angle) one winglet is horizontal the other within 30 degrees of vertical. The latter winglet adds some useful keel area. The question I ask you to think about is which one is controlling the keel tip vortex by a plate effect... The answer is, of course, that they are too small to do that well and they are really workin in conjunction with the bulb (that provides an endplate effect). I don't think I'm giving TNZ design secrets away but, what these long thin winglets are doing "flying" in the keel vortex which is why they are at the back of the bulb. They extract lift and energy from the vortes and increase overall keel efficiency. If they actually generate a lift (or a torque) in a direction oppostite to that of the votex then they rob it of energy and return energy to the keel system (or reduce parasitic drag if you prefer). Second they are not symmetrical in section. The winglet with the negative angle of attack generates less negative lift in the vortex than that with the postive angle. The net effect is postive lift and again vortex energy robbing. OK? Cheers MC |
How keel winglets really work
Sorry, the discussion is getting confused. There are two issues, the
plate effects and winglets that fly. I mentioned AC yachts as examples of flying winglets -most other boats just have simple plates. See my discussion of winglets elsewhere in this thread. Cheers Matt Colie wrote: Sorry, But the wings are an AC keel are not intended to function of an aircraft winglet. The function of the aircraft application has been effectively described here, the the wings on a keel have a primary function that is different. The tip vortices are pretty much confounded buy the huge bulb (much like an aircraft tip tank will do). The wings are actually designed to provide additional lift to windward that is not dependent on the keel blade attack angle. That is why they pay so much attention to the attack angle of the wings during the set up and trials. They have to play out a dual between more angle for more lift to weather when heeled and less angle for less drag with the boat upright going to leeward. As the current IACC rules have not allowed this to be trimed underway, they only get to set it once per race, and if you listen to the discussions going on the background, you will here them talk about the adjustment as three-quarters or one-half degree. Matt Colie (certifications available on request) Nav wrote: Oz wrote: On Mon, 02 Feb 2004 11:27:49 +1300, Nav scribbled thusly: DSK wrote: Navvie wrote: From: http://www.djaerotech.com/dj_askjd/d.../wingfin1.html This is from a model airplane web site, and some of the terminology for hydrodynamics is rather different. For one thing, we don't talk about the "helix angle" of underwater foils. For another, attempting to get a net forward (or windward) lift component from keel winglets isn't going to work because they have to sail on both tacks. Yep, that's why they are on both sides. Cheers Which chucks you whole spiel out the window. Ever see a jet with winglets that extend to the lower side of the wing? Never flown inverted on a 747-400 no. Come to that I've never flown on any inverted jet, but if they were flying both sides up with equal frequency you can bet there would be winglets on top and bottom... It really isn't all about the end plate effect you know. Look at AC winglets -its all about controlling the parasitic drag from the keel tip. OK? Cheers |
How keel winglets really work
Peter Wiley and Donal don't read such books Jax.
Cheers JAXAshby wrote: One case where the movie was just as good or better than the book, a rare event. ALL James Bond movies were better than ANY James Bond book. |
How keel winglets really work
Nav wrote:
... Did you see the dihedral on current IACC winglets? It's up to about 30 degrees (by eye). That neans when the heel is 30 degrees (a typical 'powered up' design heel angle) what? You need a new protractor. I din't see any IACC boats sailing at heel angles of over 20 steadily, much less 30. And IMHO 12 ~ 15 is much more common. Anyway, I don't remember the details of the keel winglets this time around, other than one whale tail design that looked cool but I don't remember which boat it was on. ......The question I ask you to think about is which one is controlling the keel tip vortex by a plate effect... The answer is, of course, that they are too small to do that well and they are really workin in conjunction with the bulb (that provides an endplate effect). I don't think I'm giving TNZ design secrets away but, what these long thin winglets are doing "flying" in the keel vortex which is why they are at the back of the bulb. They extract lift and energy from the vortes and increase overall keel efficiency. If they actually generate a lift (or a torque) in a direction oppostite to that of the votex then they rob it of energy and return energy to the keel system (or reduce parasitic drag if you prefer). Does the winglet no produce a tip vortex of it's own? And wouldn't that counter the one from the main section of keel foil? Anyway, this is a lot closer to what happens (as I understand it) than what you were saying the first time around. ... Second they are not symmetrical in section. The winglet with the negative angle of attack generates less negative lift in the vortex than that with the postive angle. The net effect is postive lift and again vortex energy robbing. OK? Dude, check your geometry. Each winglet may not be symmetrical, but they are paired. The overall design *is* symmetrical. Any beneficial effect they have on keel efficieny is in the area of reduced drag and increased lift on the main keel section. If the winglets prodcued net lift themselves, then it would be pulling the boat down in the water, which would not help speed. DSK Cheers MC |
How keel winglets really work
DSK wrote: Nav wrote: ... Did you see the dihedral on current IACC winglets? It's up to about 30 degrees (by eye). That neans when the heel is 30 degrees (a typical 'powered up' design heel angle) what? You need a new protractor. I din't see any IACC boats sailing at heel angles of over 20 steadily, much less 30. And IMHO 12 ~ 15 is much more common. Lord, why don't you think about what I write. I said powered up! Next you will be saying powered up is not where the boat is at max power. Cheers |
How keel winglets really work
DSK wrote: Nav wrote: ... Second they are not symmetrical in section. The winglet with the negative angle of attack generates less negative lift in the vortex than that with the postive angle. The net effect is postive lift and again vortex energy robbing. OK? Dude, check your geometry. Each winglet may not be symmetrical, but they are paired. The overall design *is* symmetrical. Any beneficial effect they have on keel efficieny is in the area of reduced drag and increased lift on the main keel section. Yes, I said the lift was coupling energy back into the keel. Why do you have to say the same thing and yet not agree? Now please try to think about it a bit more. Look at the vortex down it's axis and imagine an (e.g.) Clarke y type section across the vortex. Does it produce more lift on one side than the other? The key is that the vortex gives one side of the wing a negative angle of attack and the other an equally postitive angle of attack. Now couple that to an assymetric type section (e.g. Clarke Y) and what have you got? Do you get it now? Cheers |
How keel winglets really work
Few realize that the lift resulting from a fart puts undue pressure upon the
sphincter. One must not forget the extra energy garnered from the convergent/divergent airflow across the sphincter. Is mass conserved in this case? "Nav" wrote in message ... The Professor wrote: What happens when , at low airspeed, one injects air into the airflow? Depends on injection flow rate and position doesn't it? If it's a fart people may complain. Cheers |
How keel winglets really work
"Nav" wrote in message ... Peter Wiley and Donal don't read such books Jax. Hey, I don't read much. Did you read Nathaniel's Nutmeg as a result of my recommendation? Regards Donal -- |
How keel winglets really work
"The Professor" wrote in message ink.net... Few realize that the lift resulting from a fart puts undue pressure upon the sphincter. One must not forget the extra energy garnered from the convergent/divergent airflow across the sphincter. Is mass conserved in this case? Occasionally, and very embarrassingly! Regards Donal -- |
How keel winglets really work
Energy from the flow is lost as sound.
Cheers The Professor wrote: Few realize that the lift resulting from a fart puts undue pressure upon the sphincter. One must not forget the extra energy garnered from the convergent/divergent airflow across the sphincter. Is mass conserved in this case? "Nav" wrote in message ... The Professor wrote: What happens when , at low airspeed, one injects air into the airflow? Depends on injection flow rate and position doesn't it? If it's a fart people may complain. Cheers |
How keel winglets really work
Donal wrote: "Nav" wrote in message ... Peter Wiley and Donal don't read such books Jax. Hey, I don't read much. Did you read Nathaniel's Nutmeg as a result of my recommendation? No. Cheers. |
How keel winglets really work
Donal wrote:
Did you read Nathaniel's Nutmeg as a result of my recommendation? No, I read it because it was given to me as a gift. DSK |
How keel winglets really work
Nav wrote:
... I said powered up! If you think 30 degrees heel is "powered up" then there's really no point in discussing it. DSK |
IACC Boat speed at 30 degrees heel?
DSK wrote: Nav wrote: ... I said powered up! If you think 30 degrees heel is "powered up" then there's really no point in discussing it. Lord what a self serving, devious and misleading (for others) response. Fact: At least two syndicates revealed CFD calculations for ~30 degrees heel and boatspeed about ~10 knots. That's pretty powered up I'd say. I can also tell you typical trim tab angles for those conditions but I'm sure you wouldn't want to know about either. If you come here even you can sail on IACC yachts (for a modest price) and find out what an IACC yacht powered up feels like. It's a blast I promise. If you don't belive me try a google search -the papers are out there. Cheers |
IACC Boat speed at 30 degrees heel?
Nav wrote:
Lord what a self serving, devious and misleading (for others) response. More insults. Thanks. Fact: At least two syndicates revealed CFD calculations for ~30 degrees heel and boatspeed about ~10 knots. That's pretty powered up I'd say. I can also tell you typical trim tab angles for those conditions but I'm sure you wouldn't want to know about either. Actually I am interested in any info (from the real world, I mean, not JAXworld) that anybody can provide. It's a big part of why I am here. The fact that you constantly allude to how much you know, yet never actually explain anything or post actual info and refuse to provide links, is very revealing. Anyway, if the IACC syndicate designers calculated data for 30 degress, does that mean they intend the boats to actually sail at that angle, or that this is the fastest angle of heel? .... If you come here even you can sail on IACC yachts (for a modest price) and find out what an IACC yacht powered up feels like. It's a blast I promise. What makes you think I haven't already sailed an IACC boat, without having to pay? In any event, I would not want to sail one that kept breaking. If you don't belive me try a google search -the papers are out there. Why not post the links? BTW did you ever email any of the people you said you were going to? DSK |
IACC Boat speed at 30 degrees heel?
DSK wrote: Nav wrote: Lord what a self serving, devious and misleading (for others) response. More insults. Thanks. Fact: At least two syndicates revealed CFD calculations for ~30 degrees heel and boatspeed about ~10 knots. That's pretty powered up I'd say. I can also tell you typical trim tab angles for those conditions but I'm sure you wouldn't want to know about either. Actually I am interested in any info (from the real world, I mean, not JAXworld) that anybody can provide. It's a big part of why I am here. Young America was designed for 6 degrees trim at 10 knots boatspeed and 30 degrees heel. That's about as fast they expected to go when powered up here. Cheers |
IACC Boat speed at 30 degrees heel?
DSK wrote: Nav wrote: Lord what a self serving, devious and misleading (for others) response. More insults. Thanks. I'd say it's quite mild given the tone of your response. Others might have referred to your interest in animals but I'm too polite to stoop to such gutteral behaviour. Cheers |
IACC Boat speed at 30 degrees heel?
Nav wrote:
Young America was designed for 6 degrees trim at 10 knots boatspeed and 30 degrees heel. That's about as fast they expected to go when powered up here. 6 degrees trim on what... the keel trim tab? That sounds like a heck of a lot. Bear in mind that at 30 degrees heel, the projected sail area and keel foil area are only 85% of actual area. Hard to claim that this is when the boats are most efficient. Anyway, long narrow boats like the IACC class and the old 12s too tend to sail at higher angles of heel than more normally proportioned boats. I still think 30 degrees is a bit of an overstatement. DSK |
IACC Boat speed at 30 degrees heel?
DSK wrote: Nav wrote: Young America was designed for 6 degrees trim at 10 knots boatspeed and 30 degrees heel. That's about as fast they expected to go when powered up here. 6 degrees trim on what... the keel trim tab? That sounds like a heck of a lot. Bear in mind that at 30 degrees heel, the projected sail area and keel foil area are only 85% of actual area. Hard to claim that this is when the boats are most efficient. Who said anything about efficient. Powered up refers to power! Anyway, long narrow boats like the IACC class and the old 12s too tend to sail at higher angles of heel than more normally proportioned boats. I still think 30 degrees is a bit of an overstatement. Wot only a 'bit' now is it? Just yesterday you rubbished it! Doug, lots of boats are only fully powered up at 30 (or more) degrees heel. Of course as a dingly sailor you wouldn't know that but it's really true. Let me paint a typical picture for you: At that 30 degrees heel the boat is alive and really punching through waves to windward. Windspeeed is probably about 18-20 knots with gusts to 25. The rail is getting wet with occasional waves over the bow and it's the limit where more wind means you'll probably have to ease the main sheet (or reduce sails) to maintain good control and boat speed. It's a fun place to sail -powered up! Ask any of the others -they've sailed there I'm sure! Cheers |
IACC Boat speed at 30 degrees heel?
Anyway, long narrow boats like the IACC class and the old 12s too tend
to sail at higher angles of heel than more normally proportioned boats. I still think 30 degrees is a bit of an overstatement. Nav wrote: Wot only a 'bit' now is it? Just yesterday you rubbished it! Doug, lots of boats are only fully powered up at 30 (or more) degrees heel. OK, I am still not sure what you mean by "powered up." It sounds to me like you are relishing the feeling of heeling too much. It's fun, but it's really not fast. .... Of course as a dingly sailor you wouldn't know that but it's really true. Spoken like one whose experience in racing class dinghies is limited to embarassing capsizes within 100 yards of the club dock. Let me paint a typical picture for you: At that 30 degrees heel the boat is alive and really punching through waves to windward. At 30 degrees heel, the boat is heeling too much. It is "punching" through waves because the hull presenting a set of awkward angles. Other boats have depowered a little and are going faster. ... Windspeeed is probably about 18-20 knots with gusts to 25. The rail is getting wet with occasional waves over the bow and it's the limit where more wind means you'll probably have to ease the main sheet (or reduce sails) to maintain good control and boat speed. It's a fun place to sail -powered up! Ask any of the others -they've sailed there I'm sure! Sailing rail-down and driving hard is a lot of fun. But it's not the way boats sail their best. Personally I like spinnaker reaches with threatening wipe-outs on every wave. But it's a rare indulgence because it isn't really the right way to do things. In fact, in one of our 'powered up' Johnson 18 photos it was said that it looked like we didn't know what we were doing. Fresh Breezes- Doug King |
IACC Boat speed at 30 degrees heel?
DSK wrote: Anyway, long narrow boats like the IACC class and the old 12s too tend to sail at higher angles of heel than more normally proportioned boats. I still think 30 degrees is a bit of an overstatement. Nav wrote: Wot only a 'bit' now is it? Just yesterday you rubbished it! Doug, lots of boats are only fully powered up at 30 (or more) degrees heel. OK, I am still not sure what you mean by "powered up." It sounds to me like you are relishing the feeling of heeling too much. It's fun, but it's really not fast. .... Of course as a dingly sailor you wouldn't know that but it's really true. Spoken like one whose experience in racing class dinghies is limited to embarassing capsizes within 100 yards of the club dock. Let me paint a typical picture for you: At that 30 degrees heel the boat is alive and really punching through waves to windward. At 30 degrees heel, the boat is heeling too much. It is "punching" through waves because the hull presenting a set of awkward angles. Other boats have depowered a little and are going faster. Have you done any big boat sailing or been in a race in windy conditions? Why not read the book whose URL I posted and then come back on it. Better yet go back to the classic literature and look at the tests of the Gimcrack. She was fastest at 30 degrees and was no faster at 35 degrees. That's still a correct rule of thumb for most fast cruiser racers today. Perhaps Donal would like to post the figs. for his boat -if he's got them? Another slam dunk. Cheers |
IACC Boat speed at 30 degrees heel?
Nav wrote:
Have you done any big boat sailing or been in a race in windy conditions? Why, of COURSE not, Navvie. Never! But then you are a liar, so you think I must be one too... .. Why not read the book whose URL I posted and then come back on it. So you're saying that you base your judgement solely on what you've read in books? ... Better yet go back to the classic literature and look at the tests of the Gimcrack. She was fastest at 30 degrees and was no faster at 35 degrees. That's still a correct rule of thumb for most fast cruiser racers today. Not in my experience. Most boats like about 12 degrees of heel. The Soling (a relatively narrow boat) sailors I know say their boats like 18. I would generalize to say that narrower & heavier boats like more heel, but in cases where the keels and/or rigs get dramatically less efficient with increased angle, it would be beneficial to take some serious sailing tests to determine the desirable range of heel for most conditions. One big limiting factor is the helm. Increasing heel increases weather helm. That has to be counteracted with the helm. A slight weather helm is nice, a lot is bad. It's slow and it can make the boat hard to control. Perhaps Donal would like to post the figs. for his boat -if he's got them? Another slam dunk. Maybe you should be less concerned with "slam dunks" and more concerned with actual sailing? Just a suggestion. Fresh Breezes- Doug King |
IACC Boat speed at 30 degrees heel?
DSK wrote: Nav wrote: Have you done any big boat sailing or been in a race in windy conditions? Why, of COURSE not, Navvie. Never! Well it's good to know my suspicions were correct. So you're saying that you base your judgement solely on what you've read in books? It was you that was seeking references wasn't it? Don't you like definitive references that support my views? How strange. Perhaps you are the sophist Jax suggested? Cheers |
IACC Boat speed at 30 degrees heel?
DSK wrote: Not in my experience. Most boats like about 12 degrees of heel. The Soling (a relatively narrow boat) sailors I know say their boats like 18. I would generalize to say that narrower & heavier boats like more heel, but in cases where the keels and/or rigs get dramatically less efficient with increased angle, it would be beneficial to take some serious sailing tests to determine the desirable range of heel for most conditions. Bluster all you like but 30 degrres for max boat speed is still quite usual. How about a designer of the Volvo 60: "Roll, baby, roll … Volvo 70’s must be designed to stringent large-heel-angle stability criteria. While a canting keel increases stability (or righting moment) dramatically under typical sailing conditions (say 30 degrees of heel), its offset CG actually works against a self-righting tendency at large, knockdown heel angles. Accordingly, Volvo 70 Rule developers have closely examined limitations on hull displacement and beam that affect form stability, with additional limitations on keel weight and keel swing angles. Each yacht shall have a designer-calculated limit of positive stability greater than 115 degrees, with appendages positioned in a worst-case scenario. In addition, each boat must successfully self-right from a 180-degree inversion using only manual power to articulate the keel." http://www.perrottidesign.com/new_Volvo_Open70.html Cheers |
IACC Boat speed at 30 degrees heel?
DSK wrote: ... Better yet go back to the classic literature and look at the tests of the Gimcrack. She was fastest at 30 degrees and was no faster at 35 degrees. That's still a correct rule of thumb for most fast cruiser racers today. Not in my experience. Most boats like about 12 degrees of heel. The Soling (a relatively narrow boat) sailors I know say their boats like 18. I guess you would not have overtaken the race leader -look at this: http://www.sevenoceans.com/SoloAroun...Leg1/Day30.htm Cheers |
IACC Boat speed at 30 degrees heel?
DSK wrote: Not in my experience. Most boats like about 12 degrees of heel. Aha that'll be your dinghy experience showing itself again. In a bigger keel boat you won't come anywhere except last if you limit yourself to 12 degrees. Now, boat's don't 'like' anything. They are just imanimate objects really. The question is, what is the most common design angle? (I've already posted one ref. Why don't you check Barnaby 'Basica naval archtiecture' too and you'll see it's 30 degrees.) Heeling is not by itself a bad thing -it means that lots of power is being taken from the wind if the boat is trimmed properly. The general idea is that provided the heel angle is moderate (say 30 degrees) the reduction in projected fin area is not too serious... Cheers |
IACC Boat speed at 30 degrees heel?
DSK wrote: Anyway, long narrow boats like the IACC class and the old 12s too tend to sail at higher angles of heel than more normally proportioned boats. I still think 30 degrees is a bit of an overstatement. Nav wrote: Wot only a 'bit' now is it? Just yesterday you rubbished it! Doug, lots of boats are only fully powered up at 30 (or more) degrees heel. OK, I am still not sure what you mean by "powered up." It sounds to me like you are relishing the feeling of heeling too much. It's fun, but it's really not fast. Wrong again. Look at the references. Cheers |
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