Catamaran Racing Association of Michigan

Apparent Wind
Definition: Apparent Wind is the wind the boat experiences as it moves through the true wind. This would be the direction and strength of the wind you feel on your cheek or the direction the wind indicator points as you’re sailing.

True Wind is the direction and speed of the wind over the water. This is what you see on the flag of an anchored boat or the ruffles on the water.When you’re stopped, true wind and apparent wind are exactly the same. Think of riding a bike on a calm day. As soon as you start moving, the apparent wind is the breeze you feel on your face from your own speed.

If there is a small breeze coming from the side, your forward speed gets added to the wind speed, and the apparent wind shifts forward (toward the front of the boat) compared with the true wind. The faster the boat goes, the further the forward shift. As an example, a boat sailing 10kts sideways to the true wind (a 90deg beam reach) in a 10kt breeze will see an apparent wind of 12kts at about 45deg. If the boat speed increases to 15kts, then the apparent wind increases to 18kts and its angle decreases to 33deg. The boat would feel like its pointing (close to the wind) even though it’s on a beam reach relative to the true wind.

The magic of apparent wind: As you can see, part of the boat speed gets added to the true wind speed. This can create a virtuous cycle that will continue until the apparent wind shifts too far forward or the drag on the hulls starts to dominate. Low-drag boats like catamarans can therefore go faster than the wind on some points of sail! Super low-drag ice boats can manage more than 4X the speed of the wind in certain conditions. Imagine that on a blustery 20mph winter afternoon! Catamarans are more modest, and the capability depends on the boat design. Most are in the 1.2 to 1.8x range on a beam or slightly deeper reach.