Is it fair to say that if the wind is coming from a 90 % angle, that the more the boat leans to the side (what's the right term for this?), the faster it goes?
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- Jan 22, 2008
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and the reason
that the moderate heel does increase speed, is that for non planing boats, the max speed is derived by the waterline length of the hull. By heeling, the wetted surface length of the hull (waterline length) is thereby increased. The more it increases however, (theoretically until the boat is on its side), the sail is less affected by the wind, so there is no drive. As such, the compromise is somewhere between 18 and 20 degrees depending on the shape of the hull. With a GPS on board, you should be able to see the increase in speed with heel, then at a certain point, it levels off, then if heel increases, the speed decreases. By this time however, the boat is rounding up and righting itself again. As well, with a well heeled boat, you will find yourself fighting the tiller thereby inducing drag. Hope this further explanation helps.
that the moderate heel does increase speed, is that for non planing boats, the max speed is derived by the waterline length of the hull. By heeling, the wetted surface length of the hull (waterline length) is thereby increased. The more it increases however, (theoretically until the boat is on its side), the sail is less affected by the wind, so there is no drive. As such, the compromise is somewhere between 18 and 20 degrees depending on the shape of the hull. With a GPS on board, you should be able to see the increase in speed with heel, then at a certain point, it levels off, then if heel increases, the speed decreases. By this time however, the boat is rounding up and righting itself again. As well, with a well heeled boat, you will find yourself fighting the tiller thereby inducing drag. Hope this further explanation helps.
No....It's not fair to say that.!
Excessive heeling is like high flying a hull on a catamaran. It looks cool and can be an exciting ride but it's not faster sailing. I recommend you acquire a good sail trim book such as Tom Whidden's "The Art and Science of Sails". Don Gillette's Sail Trim Guide is good too.
Excessive heeling is like high flying a hull on a catamaran. It looks cool and can be an exciting ride but it's not faster sailing. I recommend you acquire a good sail trim book such as Tom Whidden's "The Art and Science of Sails". Don Gillette's Sail Trim Guide is good too.
Have Trouble with the "Reason"
When heeling is discussed, the reason for increased speed with small amount of heeling is frequently attributed to the increased waterline length. Apparently this was done for some boat designs, but it does not compute for most. For example with a boat with a 21' waterline length, the hull speed is 6.14k. If you increase the waterline length to 22' with heeling, the hull speed increases to 6.29k. Not hardly a major speed increase with what is a very unlikely amount of waterline length increase. I tried to come up with a measured increase in waterline length in my MAC 23 with heeling. I could not get any more than a few inches, if that. I believe the reason may be more simple than this. The further you heel, the more drag from the rudder due to weather helm and the sails have dumped some of there power. With a small amount of heel, those effects are minimized while still taking advantage of the increased power.
When heeling is discussed, the reason for increased speed with small amount of heeling is frequently attributed to the increased waterline length. Apparently this was done for some boat designs, but it does not compute for most. For example with a boat with a 21' waterline length, the hull speed is 6.14k. If you increase the waterline length to 22' with heeling, the hull speed increases to 6.29k. Not hardly a major speed increase with what is a very unlikely amount of waterline length increase. I tried to come up with a measured increase in waterline length in my MAC 23 with heeling. I could not get any more than a few inches, if that. I believe the reason may be more simple than this. The further you heel, the more drag from the rudder due to weather helm and the sails have dumped some of there power. With a small amount of heel, those effects are minimized while still taking advantage of the increased power.
Dan
The other part of the equation is the reduced wetted surface area. As the boat heels, the waterline increases and the wetted surface area decreases so the total drag coefficient of the hull is reduced. There are also subtle changes to the flow of water over the keel and rudder which increase lift, again adding to boat speed. All of these changes have deminishing returns as drag is factored in. And we have not factored in the changes through the other fluid, air. The total result is that optimal 18 to 20 degrees.
The other part of the equation is the reduced wetted surface area. As the boat heels, the waterline increases and the wetted surface area decreases so the total drag coefficient of the hull is reduced. There are also subtle changes to the flow of water over the keel and rudder which increase lift, again adding to boat speed. All of these changes have deminishing returns as drag is factored in. And we have not factored in the changes through the other fluid, air. The total result is that optimal 18 to 20 degrees.
Alan
Your explanation makes sense, except for the part about waterline length increase. I have trouble believing it is due to waterline length increase. The math doesn't work, at least not for my boat. Also, if lift is taking place, which I can believe, the waterline length would decrease.
Your explanation makes sense, except for the part about waterline length increase. I have trouble believing it is due to waterline length increase. The math doesn't work, at least not for my boat. Also, if lift is taking place, which I can believe, the waterline length would decrease.
Tiller lift.
Steady heel has benefit as it allows a consistant sail set. You should be faster at a steady 25 degrees vs rolling between 5 and 20 degrees. In light air you may need 10 to 15 degrees just to get some shape in the sail. Usually anything past 20 degrees is wasting power. With moderate heeling and a slight amount of weather helm you'll also get lift from the rudder. The benefit of this lift is usually greatest at about 2 degrees of helm. Past 2 or 3 degrees and drag increases. As for the benefit of 6.14 vs 6.29 knots. A 2.4% speed increase would gain you about 50 yards every hour. To some this would be considered a significant benefit on race night.
Steady heel has benefit as it allows a consistant sail set. You should be faster at a steady 25 degrees vs rolling between 5 and 20 degrees. In light air you may need 10 to 15 degrees just to get some shape in the sail. Usually anything past 20 degrees is wasting power. With moderate heeling and a slight amount of weather helm you'll also get lift from the rudder. The benefit of this lift is usually greatest at about 2 degrees of helm. Past 2 or 3 degrees and drag increases. As for the benefit of 6.14 vs 6.29 knots. A 2.4% speed increase would gain you about 50 yards every hour. To some this would be considered a significant benefit on race night.
Most boats are probably faster sailed flat
The unavoidable side affect of catching the wind is that the boat heels. I don't think that you should be very concerned with the amonut of heel. The main concern should be triming the sails. Triming the sails too close will result in more heeling and less speed. Beginners always try to pull in on the sheets for more speed and it just doesn't work like that. As you pull in the sheets more and more of the winds energy is used to lift the keel this is energy not being used for forward motion!! It is unavoidable to lose some energy lifting the keel but the more energy that is converted to forward speed the better. In higher winds I try to get a flatter sail and pull in just enough to get a good shape on the sail. The amount of heeling doesn't enter into the equation unless it is so much that the wife gets nervous. Then it is time to reef. My hull speed is about 7.2 knots and I can achieve that speed with about 15 knots of wind. If the wind goes to 20 knots I can keep that speed with a reef. Without a reef I get more heeling but little increase in speed. If it is a gust every 10-15 minutes we just enjoy the heeling but if it is a steady 20 knots we reef. Many boats are now very beamy and with a beamy boat flatter is faster. IMHO the only boats that work better with some heel are the narrower blue water type of boats but even then heeling doesn't make them go faster catching the wind more efficently makes for more speed and heeling is a side effect. Watch your sails!!! Tom
The unavoidable side affect of catching the wind is that the boat heels. I don't think that you should be very concerned with the amonut of heel. The main concern should be triming the sails. Triming the sails too close will result in more heeling and less speed. Beginners always try to pull in on the sheets for more speed and it just doesn't work like that. As you pull in the sheets more and more of the winds energy is used to lift the keel this is energy not being used for forward motion!! It is unavoidable to lose some energy lifting the keel but the more energy that is converted to forward speed the better. In higher winds I try to get a flatter sail and pull in just enough to get a good shape on the sail. The amount of heeling doesn't enter into the equation unless it is so much that the wife gets nervous. Then it is time to reef. My hull speed is about 7.2 knots and I can achieve that speed with about 15 knots of wind. If the wind goes to 20 knots I can keep that speed with a reef. Without a reef I get more heeling but little increase in speed. If it is a gust every 10-15 minutes we just enjoy the heeling but if it is a steady 20 knots we reef. Many boats are now very beamy and with a beamy boat flatter is faster. IMHO the only boats that work better with some heel are the narrower blue water type of boats but even then heeling doesn't make them go faster catching the wind more efficently makes for more speed and heeling is a side effect. Watch your sails!!! Tom
Dan, check out older boat designs
Dan, modern hull designs don't achieve as much increase in waterline length with heeling as older designs. Modern, almost vertical bows and wide beams carrying the width all the way back to the transom won't do it. But if you check out older designs with long overhangs on both ends you will see there is a significant increase in waterline when heeled. Kevin
Dan, modern hull designs don't achieve as much increase in waterline length with heeling as older designs. Modern, almost vertical bows and wide beams carrying the width all the way back to the transom won't do it. But if you check out older designs with long overhangs on both ends you will see there is a significant increase in waterline when heeled. Kevin
Good Discussion
I love this kind of discussion. No one questioning anyone’s intelligence. Just a good discussion. I can’t help but learn from it. Unfortunately, I have to leave about noon (10am PST) for several days. An increase in hull speed may be more dramatic in older designs, but most of us do not sail older designs. First the lifting effect of the rudder. I can’t say whether this is a net gain or loss, but any lift is at the expense of drag. I do know when that when heel is excessive, there is a tremendous amount of drag from the rudder. At ten to fifteen degrees of heel, there is little drag. Again, any lift will shorten the waterline length. This is especially true for my MAC 23. Near the stern, the angle between the water and the hull is very small, maybe 10 degrees. The near vertical part of the stern is above the water. Any lifting by the rudder will shorten the waterline length dramatically. Actually the gain over an hour with 6.14k vs 6.29k is a lot more than 50 yards. It is over 300 yards. However, that point is mute. I gave the example of a one foot difference in hull length only to show how little the water line effect is with a very large water line increase. On my MAC 23, I would estimate that it is 2” maximum and I really don’t believe there is any increase whatsoever. A 2” increase only increases the hull speed from 6.14 to 6.17. Over an hour than will get you over 50 yards. Let’s be realistic about those benefits. It would assume that you are in that configuration for an hour. That is certainly not realistic on my lake and probably not realistic for 90 percent of you. Those small increases are significant for someone who can take advantage of many such small increases. All of the races that I have watched on TV and otherwise, an effect that small would be eclipsed by small variations in the wind and other strategy.
I love this kind of discussion. No one questioning anyone’s intelligence. Just a good discussion. I can’t help but learn from it. Unfortunately, I have to leave about noon (10am PST) for several days. An increase in hull speed may be more dramatic in older designs, but most of us do not sail older designs. First the lifting effect of the rudder. I can’t say whether this is a net gain or loss, but any lift is at the expense of drag. I do know when that when heel is excessive, there is a tremendous amount of drag from the rudder. At ten to fifteen degrees of heel, there is little drag. Again, any lift will shorten the waterline length. This is especially true for my MAC 23. Near the stern, the angle between the water and the hull is very small, maybe 10 degrees. The near vertical part of the stern is above the water. Any lifting by the rudder will shorten the waterline length dramatically. Actually the gain over an hour with 6.14k vs 6.29k is a lot more than 50 yards. It is over 300 yards. However, that point is mute. I gave the example of a one foot difference in hull length only to show how little the water line effect is with a very large water line increase. On my MAC 23, I would estimate that it is 2” maximum and I really don’t believe there is any increase whatsoever. A 2” increase only increases the hull speed from 6.14 to 6.17. Over an hour than will get you over 50 yards. Let’s be realistic about those benefits. It would assume that you are in that configuration for an hour. That is certainly not realistic on my lake and probably not realistic for 90 percent of you. Those small increases are significant for someone who can take advantage of many such small increases. All of the races that I have watched on TV and otherwise, an effect that small would be eclipsed by small variations in the wind and other strategy.
Wetted area
Since the volume of a boat submerged is constant heeling may increase wetted area. A cylinder would have the least surface per unit volume But as you heel if your above waterline sections are flat you would increase wetted area. Yes I know that a sphere has the least but boats are shaped more like cylinders than spheres. Some boats are pretty flat bottomed towards the stern so it would depend upon the particular boat. If you below waterline hull is very dirty and the above is clean maybe total drag would decrease even if the wetted area increases. My hull is pretty rounded all the way to the rail except near the bow. But my last boat's hull was pretty flat above the waterline.
Since the volume of a boat submerged is constant heeling may increase wetted area. A cylinder would have the least surface per unit volume But as you heel if your above waterline sections are flat you would increase wetted area. Yes I know that a sphere has the least but boats are shaped more like cylinders than spheres. Some boats are pretty flat bottomed towards the stern so it would depend upon the particular boat. If you below waterline hull is very dirty and the above is clean maybe total drag would decrease even if the wetted area increases. My hull is pretty rounded all the way to the rail except near the bow. But my last boat's hull was pretty flat above the waterline.
There are Some People from Cities with
good memories in this discussion. My wife and I have spent a couple of months in and around Halifax over the years. We have some friends in Halifax we visit and occasionally correspond with. We bought our MAC 23 from Ted Enlund (sp??) in Panama City. He was our sailing instructor at Bonita Bay. He has, unfortunately, passed away. We miss him. He was one of our favorite people. We try to spend a month or so in Panama City each year. The last year, due to family commitments, we have been unable to do so.
good memories in this discussion. My wife and I have spent a couple of months in and around Halifax over the years. We have some friends in Halifax we visit and occasionally correspond with. We bought our MAC 23 from Ted Enlund (sp??) in Panama City. He was our sailing instructor at Bonita Bay. He has, unfortunately, passed away. We miss him. He was one of our favorite people. We try to spend a month or so in Panama City each year. The last year, due to family commitments, we have been unable to do so.
Not a single answer
At lower hull speeds (e.g. < 2/3 hull speed, depending upon hull design) the resistance against the movement of the hull through the water ("friction drag") is the main speed-killing force. In order to reduce friction drag one wants a fine bow entry and a low wetted area. Since the wetted area of most (though not all) hull shapes increases upon heeling (and the effective cross section of the bow increases) a flat boat tends to be fastest at lower speeds (i.e. in the friction drag-dominated part of the drag curve). Once we do get closer to hull speed, the friction caused by the wave pattern unavoidably created by a displacement hull ("wave drag") starts dominating since it goes up exponentially with speed. Because of the steepness of the wave drag curve here even slight increases in waterline length induced by heeling might be beneficial in spite of the concurrent increase in friction drag. Two more notes: (1) besides the increase in friction drag, most heeled vessels will also experience some loss of efficiency from their sailing rigs as well as their keels and rudders; and (2) nondisplacement vessels (or displacement vessels surfing down a wave) will be able to postpone the wave drag penalty to speeds well above hull speed. Have fun! Flying Dutchman
At lower hull speeds (e.g. < 2/3 hull speed, depending upon hull design) the resistance against the movement of the hull through the water ("friction drag") is the main speed-killing force. In order to reduce friction drag one wants a fine bow entry and a low wetted area. Since the wetted area of most (though not all) hull shapes increases upon heeling (and the effective cross section of the bow increases) a flat boat tends to be fastest at lower speeds (i.e. in the friction drag-dominated part of the drag curve). Once we do get closer to hull speed, the friction caused by the wave pattern unavoidably created by a displacement hull ("wave drag") starts dominating since it goes up exponentially with speed. Because of the steepness of the wave drag curve here even slight increases in waterline length induced by heeling might be beneficial in spite of the concurrent increase in friction drag. Two more notes: (1) besides the increase in friction drag, most heeled vessels will also experience some loss of efficiency from their sailing rigs as well as their keels and rudders; and (2) nondisplacement vessels (or displacement vessels surfing down a wave) will be able to postpone the wave drag penalty to speeds well above hull speed. Have fun! Flying Dutchman
Keep it upright
Yes Dan, these discussions can be quite enjoyable. My math-in-head was in err as the 50 yards would have been only at one knot vice six. There are many influences on speed and no expert is brave enough to claim they have it all figured out. I remember a line about the science of sailing being the most challenging of all studies. In sailing, a constantly changing solid interacts between a constantly changing liquid and a constantly changing gas. My basic rules... Water- Keep it outside of the boat. Crew- Keep them out of the water. Reefing- Do it when you 'wonder if you should'. Sheets- If in doubt, let them out. Reefed and flat are just, or almost, as fast as flogging along heeled at 30 degrees. The crew is better able to work the boat and sail trim is easier to maintain. Whenever I wait too long to reef it isn't a fun ride. My wife still mentions the time she looked down into the ocean through the cabin windows. Between her yells, all I could think of was whether or not I should let go of the siderail to hook on my lifeline. Since then I reef as soon as the question comes to mind. Excessive heel is invigorating, if that's what one's into, but it should be equally pleasing to all aboard. If you're looking for speed take a tip from the America's Cup boats and keep it upright. Their speed comes from proper sail choice and trim. They don't put up with excessive heel for very long. Unfortunately the pics that make the TV are during the moments of excessive heel.
Yes Dan, these discussions can be quite enjoyable. My math-in-head was in err as the 50 yards would have been only at one knot vice six. There are many influences on speed and no expert is brave enough to claim they have it all figured out. I remember a line about the science of sailing being the most challenging of all studies. In sailing, a constantly changing solid interacts between a constantly changing liquid and a constantly changing gas. My basic rules... Water- Keep it outside of the boat. Crew- Keep them out of the water. Reefing- Do it when you 'wonder if you should'. Sheets- If in doubt, let them out. Reefed and flat are just, or almost, as fast as flogging along heeled at 30 degrees. The crew is better able to work the boat and sail trim is easier to maintain. Whenever I wait too long to reef it isn't a fun ride. My wife still mentions the time she looked down into the ocean through the cabin windows. Between her yells, all I could think of was whether or not I should let go of the siderail to hook on my lifeline. Since then I reef as soon as the question comes to mind. Excessive heel is invigorating, if that's what one's into, but it should be equally pleasing to all aboard. If you're looking for speed take a tip from the America's Cup boats and keep it upright. Their speed comes from proper sail choice and trim. They don't put up with excessive heel for very long. Unfortunately the pics that make the TV are during the moments of excessive heel.
re: lift
Regarding lift I believe there may be a misunderstanding among some of the readers. The term lift, regarding a sailboat's hull, does not refer to how much it comes out of the water. It refers to the resistance to sideslipping. The hull, keel and rudder create a lifting effort as water flows over their foil-shaped design. In the same way that sails are like airplane wings, so are the boat's appendages under the water,and they counteract each other to provide forward motion. Rather than a vertical lift, the hull creates a horizontal lift when heeled slightly because it's curving surface is no longer perfectly symetrical in the water. You can actually steer the boat by heeling it one way or the other. Take a look at a Hobie cat's asymetrical, no daggerboard hulls and ask how they keep the boat from sideslipping.
Regarding lift I believe there may be a misunderstanding among some of the readers. The term lift, regarding a sailboat's hull, does not refer to how much it comes out of the water. It refers to the resistance to sideslipping. The hull, keel and rudder create a lifting effort as water flows over their foil-shaped design. In the same way that sails are like airplane wings, so are the boat's appendages under the water,and they counteract each other to provide forward motion. Rather than a vertical lift, the hull creates a horizontal lift when heeled slightly because it's curving surface is no longer perfectly symetrical in the water. You can actually steer the boat by heeling it one way or the other. Take a look at a Hobie cat's asymetrical, no daggerboard hulls and ask how they keep the boat from sideslipping.
Dan McGuire
You have mentioned a few times about the "lift" of the rudder or keel and the notion that this would shorten the waterline length. If I understand what you are saying, you are thinking that the "lift" is verticle to the hull of the boat pushing it up, so to speak, out of the water. This is not what lift does. The lift on the appendages is the same as that created by the sails. It is a force perpendicular to the surface that it acts on pushing sideways and forward.
You have mentioned a few times about the "lift" of the rudder or keel and the notion that this would shorten the waterline length. If I understand what you are saying, you are thinking that the "lift" is verticle to the hull of the boat pushing it up, so to speak, out of the water. This is not what lift does. The lift on the appendages is the same as that created by the sails. It is a force perpendicular to the surface that it acts on pushing sideways and forward.
No slip, no lift.
True about the lift from the keel. However, it is only generated once the boat starts to sideslip. Without sideslip the water travels the same distance along both sides of the keel. The flow of water across the keel, with slight sideslip, creates the pressure differential that produces the lift. In effect, the water acts on the keel as if it's leading edge were slightly to windward. This means that the water has farther to go on the lee side of the keel, reducing the surface pressure compared to the windward side. This lift adds Drive, but it's benefits diminish with excessive heel or sideslip. With excessive heel the sail's Drive starts to vector slightly downward and the keel's Drive starts to vector slightly upward. These opposing forces are a waste of power. To keep from overpowering one should reef or trim to dump some air, allowing the heel to remain between 10-20 degrees. The laminar flow of air on the sails and water on the keel will be aft and the Drive will be forward.
True about the lift from the keel. However, it is only generated once the boat starts to sideslip. Without sideslip the water travels the same distance along both sides of the keel. The flow of water across the keel, with slight sideslip, creates the pressure differential that produces the lift. In effect, the water acts on the keel as if it's leading edge were slightly to windward. This means that the water has farther to go on the lee side of the keel, reducing the surface pressure compared to the windward side. This lift adds Drive, but it's benefits diminish with excessive heel or sideslip. With excessive heel the sail's Drive starts to vector slightly downward and the keel's Drive starts to vector slightly upward. These opposing forces are a waste of power. To keep from overpowering one should reef or trim to dump some air, allowing the heel to remain between 10-20 degrees. The laminar flow of air on the sails and water on the keel will be aft and the Drive will be forward.
Great stuff
This is a very informative discussion. Without benefit of physics and mathematics to justify my observations, my OC-281 seems to perform best at 10 to 15 degrees heel. This also corresponds to the amount of heel that keeps the white out of my wifes knuckles and doesn't spill the beer. There are things that are more important than an extra 0.1 knot.
This is a very informative discussion. Without benefit of physics and mathematics to justify my observations, my OC-281 seems to perform best at 10 to 15 degrees heel. This also corresponds to the amount of heel that keeps the white out of my wifes knuckles and doesn't spill the beer. There are things that are more important than an extra 0.1 knot.
Freightened Wives
You folks are speaking on an intellectual plane that is way above me. The main thing that I have taken away from this discussion is that my wife isn't the only one that gets hysterical when excessive heeling takes place. That is comforting to her. It's also nice to know that I am not necessarilly sacrificing speed when I reef to avoid heeling. Thanks for the great info.
You folks are speaking on an intellectual plane that is way above me. The main thing that I have taken away from this discussion is that my wife isn't the only one that gets hysterical when excessive heeling takes place. That is comforting to her. It's also nice to know that I am not necessarilly sacrificing speed when I reef to avoid heeling. Thanks for the great info.
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