Does the asymmetrical hull form during greater heeling angles contribute to weather helm? If so, why?
Asymmetrical hull form when heeling
- Thread starter Arlyn Stewart
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John Dawson
One reason for more helm
is that you rudder becomes less effective with heavy heel and requires more pressure. The blade is canted and has an up/down factor (along with left/right) that the boat can't obey.
is that you rudder becomes less effective with heavy heel and requires more pressure. The blade is canted and has an up/down factor (along with left/right) that the boat can't obey.
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Alan
Weather helm..
..which appears and increases almost automatically as the boat heels is a result of unbalanced forces on the hull. The hull shape has relatively little to do with the weather helm. If you are looking for a more detailed investigation into hull movement and hydrodynamics, the very best book ever written on the subject is, 'Sailing Theory and Practice' by C.A. Marchaj. This book deals with every aspect of sailing theory and in my opinion has no equal.
..which appears and increases almost automatically as the boat heels is a result of unbalanced forces on the hull. The hull shape has relatively little to do with the weather helm. If you are looking for a more detailed investigation into hull movement and hydrodynamics, the very best book ever written on the subject is, 'Sailing Theory and Practice' by C.A. Marchaj. This book deals with every aspect of sailing theory and in my opinion has no equal.
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Dan McGuire
Asymmetrical Shape is Big Factor
I believe the asymmetrical shape has a large enfluence. What I don't understand is why there would be so much resisting rudder force if the hull shape was not a big factor. If you let the rudder go, the boat will rapidly head into the wind. Under those circumstances, there is no rudder effect because it is parallel to the water flow over it. As the boat is heeled over, the shape of the wetted surface of the hull becomes more like a elongated half moon shape. The shape becomes a airfoil which will provide lift and a turning motion which will cause the boat to head to weather.
I believe the asymmetrical shape has a large enfluence. What I don't understand is why there would be so much resisting rudder force if the hull shape was not a big factor. If you let the rudder go, the boat will rapidly head into the wind. Under those circumstances, there is no rudder effect because it is parallel to the water flow over it. As the boat is heeled over, the shape of the wetted surface of the hull becomes more like a elongated half moon shape. The shape becomes a airfoil which will provide lift and a turning motion which will cause the boat to head to weather.
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Ed
Yes.
I just read about this last night. It creates more drag on the leeward side, which will tend to cause the boat to round-up if not counteracted by the rudder. Too much rudder angle (about 40 degrees) will in effect act as a brake. ~ Happy sails to you ~ _/) ~
I just read about this last night. It creates more drag on the leeward side, which will tend to cause the boat to round-up if not counteracted by the rudder. Too much rudder angle (about 40 degrees) will in effect act as a brake. ~ Happy sails to you ~ _/) ~
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Tim Donley
Sailplan Balance
It seems one item overlooked here is the sailplan and its relationship to the hull. As sail area increases aft weather helm increases. As sail area increases forward lee helm prevails which can make for exciting (dangerous jibe) experiences. The design of this sailplan as related to the hull is where you really have to start the process of evaluating your helm. Relating to hull forms , beamy hulls generally have more weather helm than does a narrow beam hull of similar sail plans. The leading edge of the keel and centerboards can play a significant part as well. Sailcut can also be a factor. The sail plan has a center of effort (C.E.) that relates to the center of lateral plane (C.L.P.)of the hull underwater form. The amount of lead that the C.E. is forward of the C.L.P. varies by sailplan and hull form.More lead = lee, less lead = weather. This also changes as the hull form changes due to heeling. When you are sailing and find you have to much weather helm most of the time, you may want to consider less rake in the mast. If you find you have a lee helm at times you will want to rake the mast aft a bit. Rake of the mast is a matter of adjusting the stays accordingly but may be difficult if not impossible on some boats. A nicely balanced sailplan will have some weather helm increasing as the boat heels then with a gust will point up then fall off to where she was,that is as good as it get, she won't jibe accidently. O.K. now that I have poked the bee-hive with a stick I gotta'go. Tim
It seems one item overlooked here is the sailplan and its relationship to the hull. As sail area increases aft weather helm increases. As sail area increases forward lee helm prevails which can make for exciting (dangerous jibe) experiences. The design of this sailplan as related to the hull is where you really have to start the process of evaluating your helm. Relating to hull forms , beamy hulls generally have more weather helm than does a narrow beam hull of similar sail plans. The leading edge of the keel and centerboards can play a significant part as well. Sailcut can also be a factor. The sail plan has a center of effort (C.E.) that relates to the center of lateral plane (C.L.P.)of the hull underwater form. The amount of lead that the C.E. is forward of the C.L.P. varies by sailplan and hull form.More lead = lee, less lead = weather. This also changes as the hull form changes due to heeling. When you are sailing and find you have to much weather helm most of the time, you may want to consider less rake in the mast. If you find you have a lee helm at times you will want to rake the mast aft a bit. Rake of the mast is a matter of adjusting the stays accordingly but may be difficult if not impossible on some boats. A nicely balanced sailplan will have some weather helm increasing as the boat heels then with a gust will point up then fall off to where she was,that is as good as it get, she won't jibe accidently. O.K. now that I have poked the bee-hive with a stick I gotta'go. Tim
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tom
hull and sails
Me too!!! Just an inch or so adjustment with the forestay and backstay will affect weather helm remarkably!!!! I adjusted my Mac 26 this way to remove much of the weather helm. But hull shape is a factor. But if you increase drag on the leeward side it would make the boat turn down wind. You should turn in the direction of drag.
Me too!!! Just an inch or so adjustment with the forestay and backstay will affect weather helm remarkably!!!! I adjusted my Mac 26 this way to remove much of the weather helm. But hull shape is a factor. But if you increase drag on the leeward side it would make the boat turn down wind. You should turn in the direction of drag.
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Scott McDonald
Weather helm from heeling
There is another factor at work when the boat is heeling. The wind pushing on the sail is causing the boat to heel. At the same time the sail is generating forward thrust that is driving the boat through the water. The hull and keel provide resistance to the heeleing, but they also provide resistance to the forward thrust of the sail. At low angles of heel, the forwad thrust of the sail is in general alingment with the resistance of the hull. The result is that the boat will pitch forward slightly while underway. As heel increases, the center of effort for the sail shifts to leeward. Depending on the shape of the bottom the keel, the center of resistance may shift to windward at the same time. The offset of these forces will apply a torque to the boat, causing it to turn into the wind. This contributes to weather helm. You can notice this effect when you get a puff of wind. The puff will momentarily increase the forward thrust of the sail. If you are at a significant angle of heel, you will detect an increas in weather helm.
There is another factor at work when the boat is heeling. The wind pushing on the sail is causing the boat to heel. At the same time the sail is generating forward thrust that is driving the boat through the water. The hull and keel provide resistance to the heeleing, but they also provide resistance to the forward thrust of the sail. At low angles of heel, the forwad thrust of the sail is in general alingment with the resistance of the hull. The result is that the boat will pitch forward slightly while underway. As heel increases, the center of effort for the sail shifts to leeward. Depending on the shape of the bottom the keel, the center of resistance may shift to windward at the same time. The offset of these forces will apply a torque to the boat, causing it to turn into the wind. This contributes to weather helm. You can notice this effect when you get a puff of wind. The puff will momentarily increase the forward thrust of the sail. If you are at a significant angle of heel, you will detect an increas in weather helm.
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tom
Leeward windard??? Weather helm will develope
when the center of lateral resistence is forward of the center of effort. It is a fore and aft thing not a windard leeward thing. IMHO I agree that as you heel the center of effort on the sail changes. But also as you heel the center of lateral resistence changes as the cross section of the keel changes. I believe that is what wing keels are about. As the wing is tilted it increases the cross section of the keel exposed to lateral forces. True, wing keels lower the center of gravity but you could do that with a bulb keel. The hull shape also contributes to lateral resistence. As you heel in a beamy boat the average draft of the hull is reduced due to the flare of the hull putting more volume in less depth. I'm sure the relative contributions are very specific to a particular design of sail and hull.
when the center of lateral resistence is forward of the center of effort. It is a fore and aft thing not a windard leeward thing. IMHO I agree that as you heel the center of effort on the sail changes. But also as you heel the center of lateral resistence changes as the cross section of the keel changes. I believe that is what wing keels are about. As the wing is tilted it increases the cross section of the keel exposed to lateral forces. True, wing keels lower the center of gravity but you could do that with a bulb keel. The hull shape also contributes to lateral resistence. As you heel in a beamy boat the average draft of the hull is reduced due to the flare of the hull putting more volume in less depth. I'm sure the relative contributions are very specific to a particular design of sail and hull.
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Dan
everyone should
start their sailing lessons on a beach cat. learn to fly a hull and ride it will let you see and feel exactly what is happening the instant that it happens. esp since you are the ballast!
start their sailing lessons on a beach cat. learn to fly a hull and ride it will let you see and feel exactly what is happening the instant that it happens. esp since you are the ballast!
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Scott McDonald
Fore and Aft
Please don't misunderstand. There are many factors that can contribute to weather helm. For-and-aft balance of the sailplan is probably the most significant. It is certainly the easiest to adjust while underway. The point is that a sailplan adjusted for neutral helm at 10 degree heel will show increase in weather helm at 20 degees. The shape or performance of the sail and hull may not have changed significantly, but the alignment of thrust (sail) and drag (hull/keel) does change. The heeling effect causes a torque in the vertical axis. Imbalance in the sailplan causes the same kind of torque in the vertical axis, which is what weather helm is all about. The big difference is that sailplan balance is fore-and-aft, and can have a much bigger impact than the side-to-side effect of heeling. A minor adjustment (ease the main a bit) will easily counteract the weather helm from heeling.
Please don't misunderstand. There are many factors that can contribute to weather helm. For-and-aft balance of the sailplan is probably the most significant. It is certainly the easiest to adjust while underway. The point is that a sailplan adjusted for neutral helm at 10 degree heel will show increase in weather helm at 20 degees. The shape or performance of the sail and hull may not have changed significantly, but the alignment of thrust (sail) and drag (hull/keel) does change. The heeling effect causes a torque in the vertical axis. Imbalance in the sailplan causes the same kind of torque in the vertical axis, which is what weather helm is all about. The big difference is that sailplan balance is fore-and-aft, and can have a much bigger impact than the side-to-side effect of heeling. A minor adjustment (ease the main a bit) will easily counteract the weather helm from heeling.
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tom
windsurfer is better
With a windsurfer you tilt the sail forward to turn downwind or back to head up into the wind. ie shift the center of effort. A complicating factor is that the sail is connected to the board through your body and the mast. The best thing about learning on a windsurfer is the transition of the importance of the hull to the importance of the sail. At low wind speeds it's the hull and your weight keeping the balance. Once the wind gets up in the 20kt range you fly the sail and most of your weight is transfered to the sail. And talk about knowing instantly when you make a mistake!!!! I've been tossed 20' when in a harness. The board stops instantly when you bury it into a wave. Between inertia and wind force you get tossed. The harness takes too long to release..at least for me. A laser is the perfect learning to sail boat. It has all the sail controls. Responds instantly and is a great deal of fun. The only fault I've had with a Laser is getting it to go downwind in high winds. The tall high aspect ratio marconi sail just doesn't like the wind coming up from behind. A force 5 is equivalent. A sunfish is a lot of fun but has no sail controls other than the mainsheet to play with and develop skills. A sloop rig just complicates things when first learning.
With a windsurfer you tilt the sail forward to turn downwind or back to head up into the wind. ie shift the center of effort. A complicating factor is that the sail is connected to the board through your body and the mast. The best thing about learning on a windsurfer is the transition of the importance of the hull to the importance of the sail. At low wind speeds it's the hull and your weight keeping the balance. Once the wind gets up in the 20kt range you fly the sail and most of your weight is transfered to the sail. And talk about knowing instantly when you make a mistake!!!! I've been tossed 20' when in a harness. The board stops instantly when you bury it into a wave. Between inertia and wind force you get tossed. The harness takes too long to release..at least for me. A laser is the perfect learning to sail boat. It has all the sail controls. Responds instantly and is a great deal of fun. The only fault I've had with a Laser is getting it to go downwind in high winds. The tall high aspect ratio marconi sail just doesn't like the wind coming up from behind. A force 5 is equivalent. A sunfish is a lot of fun but has no sail controls other than the mainsheet to play with and develop skills. A sloop rig just complicates things when first learning.
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Dan McGuire
Believe Hull is most Important
All of the factors mentioned above have an effect, however, the shape of the hull relative to the water changes dramatically during a heel. During heeling, the leeward hull is more in the water than the windward hull and the curved leeward hull causes the boat to turn to windward. I know you can affect weather helm by adjusting the mast rake, but on my particular boat, I cannot move the mast forward enough to counter weather helm during exreme heeling. If I move the mast forward, there is too much lee helm when there is little or no heeling. As the boat heels, weather helm becomes dominate because the density of water is approximately 1000 times greater than air and the hull shape becomes dominate.
All of the factors mentioned above have an effect, however, the shape of the hull relative to the water changes dramatically during a heel. During heeling, the leeward hull is more in the water than the windward hull and the curved leeward hull causes the boat to turn to windward. I know you can affect weather helm by adjusting the mast rake, but on my particular boat, I cannot move the mast forward enough to counter weather helm during exreme heeling. If I move the mast forward, there is too much lee helm when there is little or no heeling. As the boat heels, weather helm becomes dominate because the density of water is approximately 1000 times greater than air and the hull shape becomes dominate.
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tom
nature or nuture???
You get like a dog chaseing it's tail. Like nature the hull is pretty much fixed at birth and can't be changed. Like nuture the sails can be changed instantly!!! Another factor is point of sail. I've noticed that my Pearson 323 can be balanced and hold a point well going into the wind. But off the wind it wants to wander and never gets quite balanced. My Macgreagor 26 was easier to balance when it was going downwind. Since the P323 is a masthead rig and the Mac was a fractional rig that may have been the difference. On the other hand when going downwind in the Mac I would raise the daggerboard in effect changing the hull shape and shiftng drag to the rudder. Other obvious differences is the Macs relatively long shallow hull and the P323's three blade fixed prop.
You get like a dog chaseing it's tail. Like nature the hull is pretty much fixed at birth and can't be changed. Like nuture the sails can be changed instantly!!! Another factor is point of sail. I've noticed that my Pearson 323 can be balanced and hold a point well going into the wind. But off the wind it wants to wander and never gets quite balanced. My Macgreagor 26 was easier to balance when it was going downwind. Since the P323 is a masthead rig and the Mac was a fractional rig that may have been the difference. On the other hand when going downwind in the Mac I would raise the daggerboard in effect changing the hull shape and shiftng drag to the rudder. Other obvious differences is the Macs relatively long shallow hull and the P323's three blade fixed prop.
Thanks for answers
Thanks to all who offered a response... Would like to exchange email with Dan McGuire, address is boatsurvey@cox-internet.com Thanks, arlyn
Thanks to all who offered a response... Would like to exchange email with Dan McGuire, address is boatsurvey@cox-internet.com Thanks, arlyn
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