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Randolph Bertin 09-21-2003 05:51 PM

heeling, weather helm and rudder control
 
I am trying to better understand some of the mechanics of sailing and would appreciate it if someone could help enlighten me concerning a situation that is probably typical in sailing.

I know that all boats perform a little differently, so let me state that I am sailing on a Beneteau 235.

Here is the situation: I am sailing close hauled in moderate winds of 5-10 knots, plus or minus, with a large genoa and full main. A puff of wind gently builds up. The boat starts heeling a little more. My understanding is that one of the turning forces on a sailboat is the shape of the hull, and that heeling causes a turning force to windward. I don''t know if this is what is meant by weather helm, but in any case, the boat does start coming up toward the wind. Naturally, I pull the tiller toward me slightly (I''m on the high/windward side of the boat) to counteract this and maintain a constant course.

The wind picks up a little more, the boat heels, continues to tend toward the wind, and thus the process continues, while I pull the tiller further and further. I look over the back of the boat and I can see that water is flowing over the rudder in a wild rush.

At a certain point, I have the tiller seemingly about as far as it can go, the boat is heeled pretty far over (maybe 30-40 degrees) and all of a sudden she rounds strongly toward the wind and comes back flat.

I am trying to figure out what exactly is going on here. It is clear I have lost control of steering the boat. What is happening with the rudder in counteracting the other turning forces?

With the boat heeled so far over, it seems that I am trying to turn the boat down into the water. Is this the limitation?

Or is it that there is not enough rudder in the water (a good bit of it is clearly visible near and above the surface) to be effective?

Or have I essentially stalled the rudder, having too high an angle of attack to have lift and so it is just acting as a large brake?

Or have I just run out of room and have no way to turn the rudder further?

Any assistance in helping me to better understand the mechanics of this situation would certainly be appreciated.

aflanigan 09-21-2003 08:37 PM

heeling, weather helm and rudder control
 
You are experiencing excessive weather helm. On your boat, like most boats, the center of effort (action of the wind pushing boat sideways, more or less) lies a little behind the center of lateral resistance (resistance of the hull and centerboard/keel to sideways motion). The rudder is turned to counteract the torque that results from this spacing between these contrary forces acting at a distance; the harder the wind blows, the greater the torque, the harder you need to pull the rudder. When you reach your catastrophic loss of control, it is either stalling/cavitation (or "aeration", as Jeff H. pointed out) of the rudder, or lifting of the rudder out of the water due to heeling, or a combination of both. Your boat has a transom hung rudder, no? which is less efficient and more prone to this "aeration" than a spade hung rudder.

Regardless of what we attribute this problem to, the solution is readily attainable. You need to reduce the torque acting on your boat by either moving the center of effort forward slightly or reducing the magnitude of the force by depowering your sails, particularly the main.

This topic came up twice in the last 2 years, and Jeff H. gave very good discussions of how to deal with excessive weather helm in each case. Here are the links:

http://members.sailnet.com/messageboard/schmessage.cfm?Forum=1&Topic=4620

http://members.sailnet.com/messageboard/schmessage.cfm?Forum=1&Topic=1768

PS if these links don''t work, just search for "weather helm" on the message board search page.

Allen Flanigan

Alexandria, VA

Randolph Bertin 09-22-2003 08:49 AM

heeling, weather helm and rudder control
 
Yes, the rudder is transom hung. There seems to be quite a bit going on, and I am just trying to sort it out. I know that if I am heeling too much generally, I need to reduce sail area (keeping a balanced sail plan). I am mostly trying to understand why the process ends with a sudden rounding up of the boat (i.e. rudder stall? not enough rudder in the water? turning the boat down into the water? combination of the above).

Thanks for the links to past discussions.

Randolph

DuaneIsing 09-23-2003 03:15 AM

heeling, weather helm and rudder control
 
Randolph,

I may not be the person to give you the definitive answer on your question, but I look at it this way:

Your boat is heeling in a gust and the weather helm continues to build. To counteract that turning force, you apply more and more corrective rudder. As the boat continues to heel, your rudder becomes less effective due to its angle (with the vertical) in the water. As you mentioned, the rudder is also getting closer to a stall from the large rotational angle it has. In the case of a transom hung rudder (like you have), less of the rudder may actually be in the water at high heel angles.

I believe at some point, all these factors diminsh the rudder authority so that the rounding up forces simply predominate. You really answered your own question, I think.

Duane


sailingfool 09-23-2003 10:42 AM

heeling, weather helm and rudder control
 
Just to ensure that this ground has been covered, I''d mention that reducing sail is not your only option to reduce heeling forces, it is the last of several options to reducing the power coming from the mainsail.

The first step to ensure that you have flattened the mainsail appropriately for the wind strength - apply maximum halyard and outhaul, and should you have these controls, Cunningham or flattening reef.. A flat sail greatly reduces power.

The second step is to lower the travel to leeward, if you have a traveller to use.

If you still have excessive heel, then reduce the mainsail with a reef. Note that excessive might be about 20 degrees on a typical boat. As your boat heels beyond the optimum point, you''ll start slipping to leeward even before your boat becomes hard to manage due to excessive weather helm.

Good luck

Jeff_H 09-23-2003 05:48 PM

heeling, weather helm and rudder control
 
And don''t forget backstay tension that tightens the forestay and depending on the design of the boat, bends the mast depowering both sails at the same time.

Jeff

JeffC_ 09-23-2003 07:19 PM

heeling, weather helm and rudder control
 
(Nice, soft touch to put the 8-ball in the pocket, Jeff…)

Randolph,

"Weather helm" is correctly the tendency for the boat to turn up into the wind: of course that is a function of relative wind pressure both fore and aft of that center of effort. We commonly <em>use</em> the term "weather helm" to describe the <u>pressure</u> we feel at the tiller when we must compensate for this tendency. It''s easy to see how these two phenonena are related…
<P>The bottom line: you pulling more and more on the tiller against the increasing pressure (weather helm), is compensating for sail trim that is growing more and more out of balance for the increasing conditions. If you try to stay on the same track, the boat has no choice but to heel over more and try to round up into the wind more.
<P>As discussed, flattening the main, blading it out w/ the traveler, and then reefing the main will cause it to de-power, letting the now-stronger <em>genoa</em> pull the bow away from the wind (the boat is rotating on its center of effort) instead of your tiller having to do it. The boat will stand up taller, and you will feel a significant reduction in weather helm at the tiller because the rudder is only deflected from center 3 or 4 degrees and you are back in balance. (A <em>slight</em> weather helm is a good rough indicator that you are correctly balanced). You will actually pick up speed because you got rid of a lot of drag from that high angle of rudder attack.
<P>Your rudder stalls for the reasons discussed above: the boat rounds up forcefully because all of a sudden all that compensating you''ve been doing with your back and biceps disappears. You''ve been drawing the bowstring back an inch at a time by continuing to haul more and more on the tiller, and now all of a sudden that bowstring is released and the boat swings up into the wind, as it increasingly has been wanting to do all along.
<P>Hope this "layman''s version" is helpful.
(Please, everyone, I know this is sloppy: I only offer this in addition to your great thread b/c I sense Randolph might appreciate a phenomenological description in additon to the physics lesson.)

mdougan 09-25-2003 11:11 AM

heeling, weather helm and rudder control
 
Followup Question:

Does the same or similar physics apply to a gaff-rigged boat? I don''t have a traveler, and no easily adjustable outhaul (laced on sail), I have running backstays (two) and a wooden mast. I do have a downhaul.

When the wind picks up, the first sail I tend to drop is the yankee jib. It''s the sail that requires the most work, as the boomed staysail is self-tacking, but from what you''re saying, reducing foresails should increase weather helm. And in this configuration, I do seem to have lots of weather-helm. When I put a single or double reef in the main, it''s much more manageable. So, is this correct? Should I reduce the main before dropping any of the foresails if I want to minimize weather helm in a gaff-rigged boat?

Thanks!
Mike

Jeff_H 09-26-2003 08:54 AM

heeling, weather helm and rudder control
 
To some extent the principles are the same excet that itis much harder to control twist in a gaff rigged sail. Many of the depowering strategies found in a bermuda rig just are not available to gaff rigs. On the other hand there are some things that you can do that Bermuda rigs can''t do. One thing that is available to you is to increase the throat halyard tension and ease the peak halyard tension. This tightens and flattens the forward portions of the sails and allows the leech of the sail to twist off and depower. On problem that gaffers generally have is that the boom is free to rise and thereby power up the lower portions of the sail. The addition of a boom vang would help with your problem.
Tightening the runner will help tension the forestay and blade out the yankee but the geometry of gaff rigs generally preclude getting a very tight forestay. Removing the yankee would increase weather helms and so is not as good an idea as taking a reef in the mainsail.

Jeff

RobGallagher 09-28-2003 09:40 PM

heeling, weather helm and rudder control
 
As a "beginer" myself I can add one thing to all the great advice that you have received so far. For some reason keeping the main pulled in tight so that it made no noise at all seemed correct to me. It also kept the rail in the water and that is fun :)

But, when sailing close hauled in a breeze the old adage "let it out till it luffs and then bring it in till it stops luffing" is not quite correct. With the main as flat as possible and the traveler eased your main might flap a bit and I think that is ok.

Playing the traveler or mainsheet a bit in a puff will also help stop you from rounding up.

I''m no expert so I hope someone will jump in and correct me if I''m wrong.


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