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Balanced Rudder

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Steve Milby
Past Commodore

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USA
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Initially Posted - 12/10/2006 : 09:39:04

The first question we should ask about a balanced rudder is, what purpose does it actually serve?

The balanced rudder was originally designed for use by the HMS Bellerophon, an 1865 British warship, driven by both steam power and a sailing rig. When a ship of such size and weight turned its massive rudder, it exerted immense pressure. Any method by which that pressure could be overcome made the ship much easier to steer, especially under auxiliary power. But, a balanced rudder has much less relevance to a small, modern sailboat.

If you've ever sailed a small dinghy, like a Laser or Force Five, you may have noticed that it's possible to balance the boat and sails so precisely that you can steer it to the right or left without touching the tiller at all, by shifting your weight from one side to the other. The same can be done with bigger keel boats like ours, even with the original rudder design. What that tells you is that a properly balanced boat with a properly balanced sailplan will have only nominal tiller pressure. It is so light that you can steer the boat with one finger. As the boat's angle of heel increases, the tiller pressure increases. So, if you want to keep the tiller pressure as light as possible, then you need only reduce your sail area and depower the sails so that the angle of heel is reduced.

What does a balanced rudder actually do for you? When a rudder moves through the water, and the water flows rapidly past it on both sides, the pressure of the water flowing across its surface resists any tendency that the rudder might have to turn. The water flow makes the rudder want to continue going straight. In order to turn the boat, you have to exert force on the tiller to turn the rudder across the flow of water. The balanced rudder has two characteristics that enable it to turn the boat more easily. The axis on which the rudder rotates is moved aft about one-third. By doing so, the lever aft of the axis is shorter, and that means that the water flow is exerting less force on a shorter lever aft of the axis. Moreover, part of the rudder's surface has been moved forward of the axis. Thus, the water flow pressure on the forward part of the rudder partially counteracts the water flow pressure on the aft part of the rudder, and that makes it easier to turn the rudder across the flow of water.

Why do so many people think a balanced rudder reduces weather helm, and makes it easier on your arms? When the boat's sailplan is well balanced and the boat is not heeling excessively, a balanced rudder has no effect whatsoever. It only comes into play when you turn the rudder across the flow of water. If the boat is heeling excessively, and the amount of weather helm increases, then you have to exert tiller pressure to keep the boat going straight. When you exert tiller pressure to counteract weather helm, you're turning the rudder across the flow of water, and a balanced rudder makes it easier to do so. But, that begs the question: "Why don't you just tune the rig and trim the sails correctly, so that the boat is not overpowered and so that it isn't heeling excessively? If you do so, you won't have excessive weather helm, and you won't have to turn the rudder across the flow of the water in order to keep the boat going straight. That weather helm, which is caused by excessive heeling, creates enormous drag which greatly reduces boatspeed.

So, to summarize, the balanced rudder makes it easier to steer a poorly tuned and trimmed boat. Even though it's easier to steer such a boat, doesn't it make more sense to tune and trim the boat properly, so that it doesn't generate that unwanted weather helm, than to go on generating all that drag below the waterline, detracting from the boat's performance? A balanced rudder deludes you into thinking the boat is well balanced when it is not.

If the boat is tuned and trimmed correctly, a balanced rudder will make it even easier to steer, but most people would probably not think the actual benefit in that case was sufficient to justify the cost.

Steve Milby J/24 "Captiva Wind"
previously C&C 35, Cal 25, C25 TR/FK, C22
Past Commodore

Edited by - on

Dave Bristle
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Djibouti
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Response Posted - 12/10/2006 : 10:46:11

I have been told by a rigger/racer who I consider by far the most expert sailor I've known, that a moderate amount of weather helm actually makes a boat faster. After noodling on that for a while, I deduced that it was by changing the angle of attack of the keel slightly to leeward (fore to aft), increasing its lift so the sails present themselves more to the wind (meaning less heel) and generate more power. (You almost have to draw a diagram of the forces involved.) That's one reason to respect a small degree of weather helm...

Another, and more important in my mind, is that weather helm acts as a "dead-man's thottle"--any less-experienced crew who's caught having to handle the boat in an adverse situation always has an easy way out--let go and the boat will stop. (The alternative could be an uncontrolled gybe.) For that reason, when I discovered that Passage, as set up by her previous owner, had a very light lee helm (under full sails and most reasonable states of trim), I corrected that by tipping the mast back slightly, which turned out to require shortening the backstay because the turnbuckle couldn't take up enough of its length.

So, now that I had a very light weather helm in moderate conditions, that meant that it was heavier as the wind picked up. The balanced rudder was a "nice" improvement, giving one-finger control in most conditions. I also noted that the improved foil design of the new rudder eliminated the fluttering that I felt with the old one. (No, I used the original pintles and gudgeons.) But actually, the reason I bought the rudder was that the original had split along its seams, and the bolt holes for the pintles had been elongated as if somebody had stepped on the top of the rudder. For security's sake, I felt we needed a new one.

We liked it a lot.

Edited by - Dave Bristle on 12/10/2006 11:04:35

bear
Admiral

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Response Posted - 12/10/2006 : 11:26:52

"Brandy" my C-250 still has a first generation rudder [beaching]. This rudder when locked straight down with the clamp that allows it
to pivot up and down has slipped on occasion allowing the rudder bottom to swing back perhaps 1" or so. What a difference that little movement makes in the arm pressure needed to turn the boat. This also tells me I had a good day sailing if this occurs. The pressures exerted to move that rudder must be tremendous. I have stepped on the locking arm to keep it tight but eventually it will pivot just that little bit in time if sailing in moderate wind. I suspect this is an unbalanced rudder at its worst.....

Edited by - on

millermg
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Response Posted - 12/10/2006 : 12:15:37

Another reason for sailing with a bit of weather helm has to do with what most of us like to call "feel". While a bit of helm does add lift, it also slows the boat down over a "neutral" helm, as any amount of water pressure on the rudder acts as a brake. However, the loss in speed is more than compensated by the ability to make the small adjustments in angle of attack and sheeting that one can only "feel" by changes in pressure in the tiller hand. A properly trimmed and balanced boat with just a bit of weather helm is actually quite easy to steer upwind with your eyes closed, you can easily feel the boat pinch and foot- subtleties that one cannot pick up with neutral helm. Try it some time, it's actually quite fun! (though best done when not singlehanding!)

Edited by - on

Steve Milby
Past Commodore

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Response Posted - 12/10/2006 : 13:32:52

When I refer to a properly tuned rig, that assumes that a properly tuned rig should have a little weather helm. I'm not suggesting that you tune your rig to have lee helm.

Suppose you had a broken arm, and you went to the doctor and he said, "I'm not going to set the broken bones, because that would be too much trouble, but I'll give you a pill to relieve the pain." You wouldn't like that idea very much.

What I'm saying is that a balanced rudder is similar to a pain pill. It relieves the pain of a poorly tuned rig and an overpowered boat, but, doesn't it make more sense to correct the underlying condition that causes the pain? Wouldn't it be better to "set the broken bone?" Shouldn't we fix the underlying problem before we take a pain pill?

All I'm saying is that I was able to tune the rig and trim the sails on my C25 so that, as the windspeed increased, the amount of tiller pressure remained light. Many times I handed the tiller to a crewmember to show them how light the tiller pressure can be, even in strong winds, when the sails are well balanced. If I can do it, anyone can do it, because I didn't do anything most of you don't know should be done, but we don't always do things as we know they should be done.

Sometimes we sail overpowered because we are racing, and we are somewhat forced to sail overpowered to stay competitive. Sometimes we sail overpowered because we enjoy the thrill of sailing rail down. Sometimes we sail overpowered because we don't want to make the effort needed to change to a smaller headsail as the wind pipes up. Sometimes we don't feel comfortable tucking in a reef while under sail, or we never got around to rigging the reefing gear.

Those are all choices we can make, and there's nothing inherently wrong with most of those choices. If we want the excitement of sailing rail down, we have every right to make that choice. But we forget that, for each of those choices, there's an alternative choice that we can make. The alternative is that we can depower the sails. If we do, the extreme tiller pressure will go away, even with the old, unbalanced rudder.

Edited by - on

dlucier
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Response Posted - 12/10/2006 : 15:22:37

An excerpt from an article by Steve Colgate on "The Balance of Hull and Sails"...

In order to sail properly, and certainly to race successfully, one must take the "balance" of the boat in consideration. By "balance," we mean the tendency of the boat's heading to either deviate or to remain straight when the helmsman releases the tiller or wheel. If the tiller is released and the boat turns away from the wind, to leeward, it is said to have "lee helm." Conversely, if the boat turns to windward it has "weather helm." If it sails straight ahead, the boat is perfectly balanced.

Balance
Though the above can be used as a guideline, older boats may have artificial weather helm. A boat will normally turn into the wind when the tiller is released because of the forces acting on the rudder. As water flows past the windward side of a rudder, "lift" is generated due to the angle of attack with the water flow. If the rudder post (which turns the rudder) is located on the leading edge of the rudder and attached to the trailing edge of the keel as on traditional sailboats, all the area aft of the post will be pulling to windward, thus tending to turn the boat into the wind. Since the water flow has traveled the full length of the keel to reach the rudder, though, the flow is not very effective as a "lift" factor.

Separated or "spade" rudders are standard now. The rudder is placed near the stern of the boat where it has the greatest leverage for steering. It is a lifting surface in itself, and since it isn't attached to the keel and is meeting fairly non-turbulent water, such a rudder is very efficient. These rudders usually are "balanced" so that the rudder post enters the rudder about one-fourth of the way back rather than being attached along the leading edge. Hopefully then, the center of the pull to windward will be right at the post and the rudder will remain straight. This reduces artificial weather helm. It also decreases true weather helm because the rudder, as a lifting surface, pulls the stern of the boat to windward to a small extent.

Excessive leeway also causes artificial weather helm. Take an extreme example of a boat slipping straight sideways through the water and making no forward motion. The water on the leeward side of the rudder aft of the rudder post pushes the rudder to windward giving the appearance of weather helm (the tiller goes to leeward as if the bow was turning to windward).

The way one can distinguish the artificial from the true weather helm is if the rudder has to be deflected from straight ahead in order to make the boat sail straight. In other words, if the tiller is being held constantly a few degrees to windward to make the boat sail straight, there is a true weather helm.

I've sailed on cruising boats with balanced spade rudders that the owners swore sailed fastest with a "neutral" helm and slowed down once they developed a slight weather helm. My observation was that though the helm felt neutral (there was no tug on it because the rudder post entered the rudder well aft of its leading edge), there was indeed a slight weather helm because the tiller was being held to windward a few degrees. When the weather helm developed to a point where the helmsman could feel it, the tiller was being held to windward at an angle large enough to increase rudder drag, thus slowing the boat down.

In most boats sailing to windward, a little weather helm is desirable. Where the rudder is attached to the trailing edge of the keel, it is obvious that the couple of degrees of rudder needed to counteract a slight weather helm tends to give the keel "lift" and reduce leeway. Too much weather helm, however, will just cause turbulence and drag.

The same holds true with the spade rudder, which gets its lift from the angle of attack the rudder makes with the water. A little weather helm cocks the rudder to windward and increases the angle of attack.

Edited by - dlucier on 12/10/2006 15:25:31

Derek Crawford
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Response Posted - 12/10/2006 : 16:32:32

I have a hard time accepting Steve's theory regarding a well-tuned and balanced rig eliminates weather helm with an unbalnced rudder.
With the original rudder, in 10k or more I had the tiller pulled under my chin there was so much weather helm. I installed the balanced rudder and WITHOUT CHANGING THE TUNING OF THE RIG had 2 finger steering in ANY wind.

Edited by - on

oldsalt
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Response Posted - 12/10/2006 : 16:41:41

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Dave Bristle
 

So, now that I had a very light weather helm in moderate conditions, that meant that it was heavier as the wind picked up. The balanced rudder was a "nice" improvement, giving one-finger control in most conditions. I also noted that the improved foil design of the new rudder eliminated the fluttering that I felt with the old one. (No, I used the original pintles and gudgeons.) But actually, the reason I bought the rudder was that the original had split along its seams, and the bolt holes for the pintles had been elongated as if somebody had stepped on the top of the rudder. For security's sake, I felt we needed a new one.

We liked it a lot.

<hr height="1" noshade id="quote"></blockquote id="quote">

I also like my balanced rudder a lot.

Edited by - on

Steve Milby
Past Commodore

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Response Posted - 12/10/2006 : 16:47:05

Don, I don't take exception to anything in the Colgate article. But it isn't "artificial" weather helm that is responsible for the extremely heavy helm that makes your arm tired. "Artificial" weather helm represents only a very small amount of the problem. In his article Colgate says:

"The way one can distinguish the artificial from the true weather helm is if the rudder has to be deflected from straight ahead in order to make the boat sail straight. In other words, if the tiller is being held constantly a few degrees to windward to make the boat sail straight, there is a true weather helm."

True weather helm is the force that causes you to have to constantly hold the tiller a few degrees to windward to make the boat sail straight, and it is that force, and not artificial weather helm, that tires your arm. The balanced rudder only deals with artificial weather helm. But, the reason why most people want a balanced rudder is because they think it will reduce the weather helm that makes their arm tired. It won't. The weather helm that makes your arm tired is true weather helm, and that's caused by sailing the boat overpowered and with excessive heel.

Edited by - on

ClamBeach
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Response Posted - 12/10/2006 : 18:07:08

"had the tiller pulled under my chin... balanced rudder... now have 2 finger steering in ANY wind."

If the rudder angle has changed radically with no other changes then there's more to the new design than just the relationship of the rudder area to the gudgeon pivots (the power steering effect). The rudder is also being a much more effective foil.

It would be a fun exercise to get a boat out sailing and swap rudders several times... record the effects.

Edited by - on

Chris Z
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Response Posted - 12/10/2006 : 19:56:03

Keep in mind, Paul Evstrom once said that the rudder is a big brake in the water, any time it is anywhere other then center, you are going slower! Weather it reduces the muscle required or not. I am guessing from what I have seen the balanced rudder is bigger, so it is a bigger brake, and a larger lever to control the weather helm.

Here is my 2 cents worth on weather helm, racing Force 5s for over ten years I understand what a tuned rig and heel of the boat. I had been sailing withe same rudder for many years and never noticed weather helm except when heeled. I had just refinished a newer light weight rudder and decided to use it for the Midwest Regionals. Got out early to test the new rudder, I noticed a slight cavitation at times. I soon figured out that I had a slight weather helm. Sailed around the corse few more times before the start to try and figure this out. Went on to win all four races that day. I contribute it solely to the ability to feel the weather helm sooner and being forced to adjust rig, heel and fore and aft weight to this great day out.

I feel my prior rudder had the same weather helm, however it was shaped and sanded to where I didn't even feel it as soon.

I guess if you are cruising, use the balanced rudder, if not use the one that gives you the best feel. Of course I say this without getting my new boat in the water yet and I am sure on a larger boat it is much harder to tune it let alone control heel. One of benefits of sailing a boat that weighs less then the sailor.

Edited by - on

oldsalt
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Response Posted - 12/11/2006 : 05:44:23

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Steve Milby
 
True weather helm is the force that causes you to have to constantly hold the tiller a few degrees to windward to make the boat sail straight, and it is that force, and not artificial weather helm, that tires your arm. The balanced rudder only deals with artificial weather helm. But, the reason why most people want a balanced rudder is because they think it will reduce the weather helm that makes their arm tired. It won't. The weather helm that makes your arm tired is true weather helm, and that's caused by sailing the boat overpowered and with excessive heel.
<hr height="1" noshade id="quote"></blockquote id="quote">

What tires your arm is a a rudder that is unbalanced with a poorly designed foil.

The very fact that the original rudder is unbalanced transmits more forces to your muscles all other factors being equal.

What was true for that old British warship in 1865 is true for your boat; a balanced rudder makes it much easier to steer and you steer with your arm.

After sailing Siver Girl with a properly tuned rig for 23 years under all conditions, including true offshore, there is no doubt that the balanced rudder is a vast improvement over the original design.

The foil shape is superior too, with all the advantages that brings to the table as well.

And no, it is not "slower" it's better.

After sailing my friend's Catalina 25 in the notorius Molokai channel off Diamond Head I suggested he install a balanced rudder. That older gentleman has had his boat since 1978 and put a lot of real sea miles under his keel in conditions that would make the average weekend sailor weep and he's written me that he couldn't believe the difference in the ease of handling with the new rudder.

The only downside I've noticed since swapping rudders is that I no longer have arms like Popeye.

Edited by - on

Steve Milby
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Response Posted - 12/11/2006 : 08:06:23

Are you guys saying that, in all conditions and all wind strengths and all angles of heel, a C25 always generates so much tiller pressure that it wears your arm out? Are you saying that the C25 is so poorly designed that it never has a light, comfortable tiller pressure? If that's what you're saying, I think it's going to come as a surprise to most of the people on this forum who own these boats. In fact, I've never sailed any boat of any make or design that sailed that bad. In moderate winds, when the C25 is sailed at a moderate angle of heel, and the sails are properly trimmed, the tiller pressure on the C25 is not so great that it requires you to pull the tiller up to your chin, nor is it even uncomfortably strong.

The boat sails nicely, with very comfortable tiller pressure, at a reasonable angle of heel, when it's not overpowered. Excessive tiller pressure only becomes a problem when the boat becomes overpowered.

That being so, a C25 owner who doesn't like excessive tiller pressure has two choices. He can either spend a few hundred dollars on a new balanced rudder, or he can keep his old rudder and adjust his sails and sail area when the wind pipes up so that the boat doesn't become overpowered.

What I'm saying is that excessive tiller pressure can be avoided by altering the way you sail the boat. We can choose to either sail it overpowered and heeling excessively or to sail it upright and well trimmed. As I said earlier, there are legitimate reasons why you might choose to sail overpowered, but it's your choice. If the wind strengthens, and the boat is overpowered and heeling excessively, and you reef the mainsail and roll up a little jib, the boat will stand up to the wind and the tiller pressure will become comfortable again.

I don't doubt that you all like your balanced rudders, or that they reduce the tiller pressure that you feel when the boat is overpowered. I'm just saying that they aren't the be all and end all. You can sail a C25 comfortably and effectively without one.

I raced and sailed mine very successfully for over 20 years with the old style rudder, and, whenever I was serious enough about racing to prep the boat properly and round up racing crew, it was always very competitive.

Edited by - on

ClamBeach
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Response Posted - 12/11/2006 : 09:06:47

I agree with Steve. I've never had a problem with excessive rudder effort or helm angle as long as the boat was properly trimmed. By that I mean not overpowered (main reefed/flattened if needed and proper size jib) and having the mainsail and jib sheeted to balance the boat fore and aft. Fastest trim/balance results in a slight weather helm, but no more than about 5 degrees of rudder angle.

Edited by - on

dlucier
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Response Posted - 12/11/2006 : 09:41:03

Steve,

You have only talked about the balance of the newer rudder (moving the pivot point), but you have not addressed the effects of the improved foil shape. This improved foil shape is what I believe is where the primary benefit of the newer rudder comes into play. Additionally, in your discussion concerning weatherhelm and sail balance, you do not mention the force (lift) that is being generated by the rudder. In Colgate's article, concerning the rudder he says, "It is a lifting surface in itself," and "as a lifting surface, pulls the stern of the boat to windward". From this, I gather a less than optimum foil shape will generate less lift resulting in more weatherhelm whereas a more efficient foil will generate more lift reducing weatherhelm for the same wind conditions.

First off, I've only sailed with a balanced rudder so I can't give a direct comparison like Dave, Derek, and Mark, but I've had other C25 owners aboard and they raved not only about the lightness of the tiller, but also how the tiller behaved in gusts. On their boats, during gusts they had to move their tillers more to windward to counteract the increased lift generated by the sails whereas on my boat, the rudder needed little to no movement to windward during the momentary gust. From this, and from what Dave, Mark, and Derek have said, I gather that the improved foil shape of the balanced rudder is able to generate considerably more lift than the original rudder.

So it appears with the newer rudder, the change in the pivot point gave us two finger control and the change in the foil shape provided more lift thereby decreasing weatherhelm.

Edited by - on

Steve Milby
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Response Posted - 12/11/2006 : 11:13:49

<blockquote id="quote">quote:<hr height="1" noshade id="quote">...you have not addressed the effects of the improved foil shape. This improved foil shape is what I believe is where the primary benefit of the newer rudder comes into play.<hr height="1" noshade id="quote"></blockquote id="quote">
I haven't talked about the improved foil shape of the balanced rudder because I don't know whether any improvement in the foil shape has been made that is sufficient to make a significant difference in the overall performance of the boat. Maybe it does and maybe it doesn't. So far as I know, if it makes a difference, it isn't enough to motivate the raters to assign different racing handicaps for the different rudders. The raters apparently think it's still fundamentally fair to allow you guys with balanced rudders to race against the old style rudders without gigging you by a few seconds per mile on your handicap ratings. If they're really as good as you guys say, maybe we should start handicapping you for using them.

But I'm not saying the balanced rudder doesn't represent an improvement over the old rudder. I'm saying that, if you're making out your Christmas wish list, and you can't afford to buy everything on the list, don't think that you can't be competitive or enjoy great sailing without a balanced rudder. For example, if I needed a new genoa, I would much rather spend my money on it than on a balanced rudder. If your genoa is blown out or sun rotted, there isn't much you can do with it, but, if you have an old style rudder, you can still use it to enjoy good sailing. If I planned on doing a lot of long distance coastal cruising, I'd much rather have a good gps, or perhaps a handheld vhf, than a balanced rudder. I'm just trying to put the benefits of a balanced rudder in perspective.

Edited by - on

cat1951
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Response Posted - 12/11/2006 : 12:00:35

As a new sailor, I am reading this thread with great interest. I wonder if someone has a picture of a balanced rudder that they can post. I went to Catalina Direct and it is the one rudder that does not have a pic.

BTW: I did a search in the archives, but did not find a thread with one in it. Maybe I just didn't find the right thread.

Thanks

Edited by - cat1951 on 12/11/2006 12:02:49

Dave Bristle
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Response Posted - 12/11/2006 : 14:21:30

Mike: I'm pretty sure Catalina Direct's C-25 Owner's Handbook has a picture comparing the balanced rudder to the original, although I gave my handbook to Passage's new owners. (The balanced design became standard equipment around 1988 or '89.) If you don't have the handbook, get one--it's the best $10 you can spend, even though it's essentially a catalog.

Don: That's not the first time I've read something by Steve Colgate that makes no sense to me (particularly referring to the 2nd and 3rd paragraphs). I really think he thinks "lift" on a sailboat foil is like lift on an airplane wing, which would be true if the foil were asymetric. Last time I looked, my keel and rudder were both symetric. I know he's a big-time racer, sailing instructor, and even helped design a nice 26-footer, and who the hell am I...

But I don't agree with some of his physics. I do agree that a keel-hung rudder is less efficient, but I believe that's mostly because of the greater turbulence around it and the directional stability of the generally longer keels (fore-to-aft) the rudder is attached to.

On the subject of the newer foil shape, I suspected (but never tried to prove) that my balanced rudder produced more steering force with less deflection--in other words, I didn't have to push the tiller as far to turn the boat at a particular rate. That's how it felt to me, although the lighter feel could have been faking me out. However, if it's true, that says the new design will generate less drag when tacking or rounding a mark--thereby helping you maintain more speed through the maneuver--but not because of the rudder balance. The lack of flutter told me that there was much less turbulence at the trailing edge of the foil--a characteristic of the new foil designs on most boats these days, and the likely explanation for the lift improvement that would explain the improved responsiveness I tried to describe. Turbulence creates drag which reduces lift which requires more turning deflection which increases drag.

Edited by - Dave Bristle on 12/11/2006 14:28:21

crcalhoon
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Response Posted - 12/11/2006 : 14:56:00

I will admit that I know nothing of physics,aerodynamics or hydrodynamics. I do know that some hot rod airplanes have a symettrical airfoil. They generate NO lift in straight ahead flight and generate the force and direction of the lift owing to angle of attack. Many of the serious aerobatic airplanes are built this way. In essence, it gives the airplane the ability to fly upside down as readily as it flies right side up. Mind, now, it only takes a degree or two of angle change to make that lift This is probably a much truer example of how a sailboat rudder works, because it too is a symetrical foil, and will only generate lift by virture of angle of attack. I think.

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Dave Bristle
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Response Posted - 12/11/2006 : 15:07:41

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by crcalhoon
 ...This is probably a much truer example of how a sailboat rudder works, because it too is a symetrical foil, and will only generate lift by virture of angle of attack. I think.
<hr height="1" noshade id="quote"></blockquote id="quote">
I think so too.

Edited by - Dave Bristle on 12/11/2006 15:08:44

cat1951
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Response Posted - 12/11/2006 : 15:20:24

Actually, from an aircraft perspective, the best comparison, is the rudder. Many of the aerobatic planes have balanced rudders that also have the pivot point behind the leading part of the rudder. It makes for tighter turns and much less energy required to make it turn quickly. I suspect that it is the same for sailboat rudders. I just left R/C flying to take up sailing and I had several planes with a counter balanced rudder. And, yes, most of the aerobatic planes like the Extra 300's, Caps, etc. have thin symetrical wings. It is the hardest type of airfoil to learn how to fly in the Remote Control arena.

Dave, next time I am at the boat, I will check the owners manual. I leave it there for reference instead of at home. Thanks for the tip.

Edited by - cat1951 on 12/11/2006 15:23:22

Dave Bristle
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Response Posted - 12/11/2006 : 17:20:22

Mike: I'm not talking about Catalina's owner's manual... I'm talking about a looseleaf binder published by Catalina Direct, the third-party supplier of many replacements and upgrades for our boats. There's a link to their site on the Links page. They and their handbook are great resources.

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dlucier
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Response Posted - 12/11/2006 : 17:53:51

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Dave Bristle
 That's not the first time I've read something by Steve Colgate that makes no sense to me (particularly referring to the 2nd and 3rd paragraphs). I really think he thinks "lift" on a sailboat foil is like lift on an airplane wing, which would be true if the foil were asymetric. Last time I looked, my keel and rudder were both symetric...<hr height="1" noshade id="quote"></blockquote id="quote">

Dave,

According to Steve Colgate, a symmetrical underwater appendage generates lift by the angle of attack (Charles referred to this earlier)

Water flowing past the hull, keel, and rudder of a sailboat is subject to the same basic rules as air flowing past the sails. The only difference between the sails and underwater appendages is that the latter are symmetrical while the former are asymmetrical. But the angle of attack (which we call "angle of incidence" for wind hitting the sails and "yaw angle" for water hitting the keel) solves the problem of getting "lift" from the keel.

A well-designed boat will have a slight weather helm which increases as the wind velocity increases. The weather helm creates "lift" for the rudder, and also gives the helmsman some "feel'' for the boat. The slight tug allows the helmsman to ease pressure on the tiller in order to let the boat come up closer to the wind. Increased pressure on the tiller makes the boat fall off away from the wind. In other words, steering is in only one direction, while the boat steers itself in the other direction. A boat is very difficult to steer well if it has to be steered up toward the wind as well as away from the wind. It is said to have no "feel."

Another reason it is desirable to have some weather helm is the fact that with it the boat will automatically head up in the puffs. This reduces heeling and maintains the angle that the wind originally made with the sails, because the apparent wind comes aft in puffs.

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oldsalt
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Response Posted - 12/11/2006 : 18:30:48

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by crcalhoon
 I do know that some hot rod airplanes have a symettrical airfoil. They generate NO lift in straight ahead flight and generate the force and direction of the lift owing to angle of attack. Many of the serious aerobatic airplanes are built this way. In essence, it gives the airplane the ability to fly upside down as readily as it flies right side up. Mind, now, it only takes a degree or two of angle change to make that lift This is probably a much truer example of how a sailboat rudder works, because it too is a symetrical foil, and will only generate lift by virture of angle of attack. I think.<hr height="1" noshade id="quote"></blockquote id="quote">

You think right.

The symetrical foils of both the rudder and the keel generate their lift from their angle of attack.

That's why you need to have some rudder angle for the rudder foil to generate the lift you need to sail upwind effectively as the rudder passes through the water.

The keel foil generates the necessary lift to sail to windward, in concert with the rudder, from the inevitable leeway your boat makes when sailing upwind. As the lift increases at the windward side of the symetrical keel and rudder foils it overcomes any increase of leeway and you're headed, somewhat "crabwise, whether reaching or upwind.

But you're always making some leeway, "crabbing" towards your destination. If you didn't, you couldn't reach or sail effectively upwind.

That's how the lift is created from these symetrical foils; angle of attack, just like an airplane.

Sailing dead downwind is, of course, another story.

That's exactly the point Steve Colgate was trying to make and it made a heck of a lot of sense when he explained it to me, an eternity ago at City Island, when his Offshore Sailing School was located in the old Ratsey and Lapthorn loft.

Edited by - on

Dave Bristle
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Response Posted - 12/11/2006 : 21:04:27

Well then I don't have a quarrel with Steve Colgate. And by the way, a while back, I referred to another guy who told me that a small degree of weather helm (such as up to 5 degrees of lee rudder) makes a sailboat faster... Apparently, the angle of attack of the keel is the key. When you steer to leeward to compensate for weather helm, the angle of attack of the rudder (to windward) shifts the keel's angle of attack very slightly to leeward. But the boat doesn't move precisely toward where the keel is pointed--its tries to move more to weather (because of the balance that's creating the weather helm), creating more pressure on the windward side of the keel--a lifting force that reduces heel and thereby makes the sails more efficient. Thus, while the underwater drag is increased somewhat, that's more than compensated for by increased power. Thus, the theory goes, the boat is actually faster with the rudder turned slightly due to weather helm. For sure, past a certain degree of imbalance, that all breaks down due to excessive drag. But my racer/rigger/friend's claim is that the right amount of weather helm makes a boat go faster, and knowing him, I'd say most likely there is something to it. And for those who want a little weather helm for feel (myself included), apparently that won't be slowing you down.

(My new boat will have a neutral helm, however.

)

Edited by - Dave Bristle on 12/11/2006 21:13:58

aeckhart
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Response Posted - 12/11/2006 : 21:42:42

All veeeeeery interesting reading, but.........now I've got a headache.

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