Centerboards vary. Mine is an older style solid bronze with minimal section and shape. It also doesn't extend to a high aspect angle. But lift, it does. Even a flat shape will lift simply due to the angle of attack through the water.

It's fairly easy to gauge this boards effect going to windward simply by the closer angle to the wind the GPS will plot lowered vs, raised. The effect of the boards lift reduces leeway. In my boats case going to windward, I can usually see something in the area of 10 degrees.

But as the boat bears off the wind, it's harder to tell it's effect. One telltale is the lifting mechanism. When the board is lifting, it's easy to feel it as the board is pushed tightly to one side of the slot. You can also feel a flutter as it's raised off the wind as it lifts, stalls...

When you bear off DDW, it releases and easily raises with the lifting mechanism. We know boards and keels are least useful DDW.

So does the measured lifting effect of a centerboard or a deep keel for that matter, stay the same throughout close hauled to broad reaching? Meaning, all or nothing? Like a light switch?

If lift is reducing leeway, is there a point, before the boat is DDW, that lift (reducing leeway) is not useful for speed?

Or put another way, what sort of keel would a designer put on a boat that would only broad reach as opposed to the same boat, that would only sail close hauled?