One day this past summer I found myself assigned to a private lesson with a student I’d taught some time ago. Unfortunately, he had allowed life to get in the way of sailing for several years.
There is a limit to the speed at which a boat can move through the water. Once a boat achieves this speed, inputting more energy into the boat—like more sail area—does not result in greater speed but can make it harder to control the vessel. Photo by Scott Alumbaugh
He then introduced me to his wife, who was coming along as crew. She had never sailed before and began to express some nervousness and concern while we were still in the office. Fitting her with foul weather gear didn’t help (“Am I going to get wet?”) and when I got her a life jacket she said, “OMG, am I going to fall off?”
This had become more complicated than I expected. It could be hard enough to refresh his skills without making him look or feel incompetent in front of his wife. And, if she didn’t like sailing, what was that going to do to their relationship? I’m not his psychiatrist or his marriage counselor, I’m just his sailing instructor! And I was hoping for a perfect sailing breeze to make everyone happy.
So, you ask, what is a perfect sailing breeze?
There is a limit to the speed at which a sailboat (or any vessel) can move through the water. (Let me emphasize through the water because vessels can plane or surf over the surface of the water and exceed this limit.) This speed limit is known as the vessel’s hull speed and is obtained using the following formula: Hull Speed (in knots) = 1.34 times the square root of the water line length of the boat (in feet). This means, of course, that big boats are inherently faster than small boats.
Once a boat achieves hull speed, inputting more energy into the boat—like bigger engines for powerboats or more sail area for sailboats—does not result in greater speed. However, this excess energy causes the boat to be overpowered and does have negative consequences. Larger bow and stern waves are raised, the wind then creates spray from these waves and blows it onto the boat, the vessel becomes more difficult to steer, and sailboats heel (or lean over) more. This is both uncomfortable and adds to the difficulty in steering.
Sailboats are designed to reach hull speed using the full mainsail and jib (considered a normal sailplan) with a wind speed of about 12 knots. I say “about 12 knots” because the movement of the sailboat either adds to or subtracts from this true wind. If you are sailing upwind, the true wind can be slightly less and the apparent wind (what you experience on the moving boat) will feel like 12 knots; and if you are sailing downwind the true wind can be slightly more and still feel like 12 knots.
By national standards, 12 knots is considered a moderate breeze; although here on San Francisco Bay it is often thought of as nice, but a little light. When the wind is not “perfect,” sailors make adjustments in order to keep the boat sailing at hull speed. In lighter winds, more sail area is needed in order to extract sufficient energy from the wind to reach hull speed. In stronger winds, sail area needs to be reduced to avoid being overpowered. At times, these adjustments can be very labor intensive.
And what did we have for my recent “refresher/I hope my wife loves sailing” class? A perfect sailing breeze, and she loved every minute of it!
Ray Wichmann, is a US SAILING-certified Ocean Passagemaking Instructor, a US SAILING Master Instructor Trainer, and a member of US SAILING’s National Faculty. He holds a 100-Ton Master’s License, was a charter skipper in Hawai’i for 15 years, and has sailed on both coasts of the United States, in Mexico, the Caribbean and Greece. He is presently employed as the Master Instructor at OCSC Sailing in the Berkeley Marina.
