Why Don’t SailGP Boats Use Spinnakers?!?!?

May 19, 2022 by Sailing Tips | Language: EN Play Time: 00:02:29 | SAILING YOUTUBERS

For most boats, launching a spinnaker and bearing away is the fastest way to get downwind, but the foiling boats they use in the America’s Cup and SailGP don’t use spinnakers, and we’re going to explain why.

Unlike old square rigged ships, modern sailboats can sail in almost any direction relative to the wind, except straight upwind, but for most boats the fastest points of sail are reaches, when you’re sailing across the wind.

This is because modern sails act like wings which produce lift, and not parachutes that produce only drag. Because of this many modern boats can sail as fast as the wind on a reach, compared to only about half as fast as the wind when sailing dead downwind. Even spinnakers act like wings and are more efficient on reaches, even though they do look like big parachutes.

Therefore most boats will sail upwind tacking through 90 degrees, but will also gybe sailing downwind, so they are still sailing across the wind, rather than dead downwind.

But to understand why foiling boats don’t use spinnakers, we need to talk a bit more about apparent wind versus true wind. When a boat is sitting stationary at the dock the true wind equals the apparent wind, and the windex will point directly at the direction the true wind is coming from.

However as the boat begins to move, the motion of the boat generates its own wind, which when combined with the true wind, creates an apparent wind that comes from further forward than the true wind. This happens for all sailboats. For a regular displacement sailboat, the apparent wind might be 10-20 degrees forward of the true wind. The sails really don’t care what the true wind is, because all they experience is the apparent wind.

But for a really fast sailboat, such as a multihull, the apparent wind might be as much as 90 degrees forward of the true wind, so in effect, some boats are always sailing in apparent wind forward of the beam, even if they are actually sailing downwind. It’s only if they stop suddenly that they will notice where the true wind is actually coming from.

The foiling SailGP and America’s Cup boats are extreme examples of this, and are literally always sailing upwind once they get going.

The sails only care about the apparent wind, and not the true wind. If we look at a typical spinnaker application chart, which shows what apparent wind ranges various spinnakers can be used in, they are really only good for apparent wind angles up to about 60 degrees.

Even on our non-foiling F-82R trimaran bends the apparent wind forward by 90 degrees, so we find ourselves using upwind sails even when we’re sailing downwind and other boats are using spinnakers.

The foiling SailGP and America’s Cup boats are much faster than this, and can sail at several times true wind speed (e.g. 45 knots of boat speed in 15 knots of wind), so they are literally always sailing upwind, regardless of the true wind, beating or close reaching at much higher apparent wind angles than any spinnaker would fly in. They are simply too fast to use spinnakers.

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