If you drive a car, think back to what they taught you about skids. The instructions they gave you about steering into the skid didn't make a lot of sense until you actually tried it - and it ran counter to your instincts. If you had listened to your instincts, you'd likely have turned the wheel in the direction that would make things worse.
When helming a sailboat, there are times that your instincts are going to catch you into doing the wrong thing. As an example of this, let's talk about steering (helming) a sailboat (or any boat, for that matter). If you want to make a hard turn to port (to the left), your instincts are to turn the wheel as far over as you can. If you are steering the motor (not a motorboat. We mean that turning the wheel turns the motor itself), then that works just fine. However, if you're steering with a rudder, it's not so cut-and-dried. To understand this, let's look at what a rudder actually is.
Like so many things on a boat, a rudder is quite often acting as a wing. It also acts as a deflector, but we'll talk about that in a moment. Let's concentrate on the wing-like aspect for a moment.
Like any wing, the wing creates "lift" (in this case, the "lift" is directed sideways rather than up and down - much like a sail). This lift then tries to push the stern of the boat in a particular direction, causing the boat to turn in the other direction. The amount of "lift" generated is governed by the shape of the "wing" (in this case, the rudder) and its "angle of attack" - basically the angle between the direction the rudder is facing and the direction that the fluid (water) is moving. It's slightly more complicated than that, but the explanation will do for this discussion. As the angle of attack increases (the wing/rudder is at more of an angle to the direction of the water motion), the lift increases. In the case of the rudder, this makes the boat turn harder. Up to a point. At some point, the angle-of-attack is too big and the wing "stalls". It basically stops generating lift and the boat doesn't turn or at least doesn't turn as hard. Instead, the drag of the "wing" increases enormously. At its worst, the rudder would be 90 degrees to the water and would act solely as a brake rather than a turning device. I can't think of any boat that lets you turn the rudder 90 degrees, but that would be the effect.
Here's a catch for you. The angle-of-attack that is too much changes depending on the speed of the boat through the water. The faster you are going, the smaller the angle of attack that is "too much". the slower you are going, the further you can move the rudder to one side before it "stalls".
Of course, there's more in play than just the "lift" of the rudder. There is also deflection. Basically, water hits the side of an angled rudder and bounces off (the water is deflected). This pushes the rudder in the opposite direction. This will reach its maximum power at about 45 degrees, regardless of boat speed (except for zero speed, in which case the rudder has zero turning power, regardless of the angle).
Where all of this comes together is, for example, during a broach. The instinct is to turn the wheel hard to counteract the turn. However, this might actually reduce the effectiveness of the rudder. It might be better to turn the rudder less than full.
So, how do you learn how much to turn the wheel? There are some simple experiments you can do. Note that, as with all scientific experiments, you want to limit the number of things that are changing. So, for this purpose, we'll do the experiments under motor rather than under sail.
- Using the motor, accelerate the boat to a reasonable speed. For most cruising boats, you might choose 5 or 6 knots.
- Turn the wheel some amount (or push the tiller over some amount) and hold it steady. Time how long it takes you to do 720 degrees (two complete circles) in the water.
- Now turn the wheel a little more (or push the tiller a little more) and time 2 more circles. Are you completing the turns faster or slower? If faster, then push the tiller or turn the wheel a bit more and time it again. At some point you'll start turning more slowly. You've now found the point of maximum turning power for your boat at that speed. If you're going a little slower, you can turn the wheel/push the tiller a bit more. If you're going faster, then you push the tiller/turn the wheel a little less.