Apparent wind is simply the wind induced by the forward speed of the boat. If you go for a drive in your car and there is no wind and you are going 30 mph, you can stick your hand out the window and feel 30 mph of apparent wind. The true wind vector must be added to the opposite of the forward speed of the boat. Thus for a given true wind speed, the faster the boat is going the closer the apparent wind angle moves toward the front of the boat. With no sail adjustment, cats need to bear off slightly in puffs at account for the change in apparent wind angle because they are moving faster. A simple example is a cat is sailing at 90 deg to the 10 kt true wind at 10 kts. The wind the crew feels on the boat is 14 kts 45 deg from the nose. Try to sketch it out on a piece of paper, it is 100% geometry. Hope this helps!
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