MAX EBB — M
y only qualifications are age, creaky joints that don't like foredeck work, and the fact that I own my own copy of the Expedition routing software. That was enough to get me signed on as navigator on a big boat racing to Hawaii. That and my willingness to write some checks to cover some of the expenses. The result was that I had surely been promoted to my level of incompetence — but that would be my secret. I do know how to drive Expedition. Routing software, however, is no help in dealing with squalls. Lee Helm turned out to be our inspector. As usual, she had volunteered to do some of the safety and equipment inspections for this race, hoping to get a crew spot. Of course, we both knew that the boat would probably finish about a day sooner if she were navigator and I were doing the inspection. Lee's job was relatively easy this time because the owner had prepared the boat very thoroughly. All that she could find deficient were lifelines not tight enough, according to the little fish scale she carries, and an out-of-date battery in the Lifesling light. There were also some lifeline stanchions that were an inch and a half too far apart, but she let us slide on that one because the wire was a size up from the required minimum. Most surprisingly, she didn't make us go through her usual live demo of the emergency rudder, probably because the owner had built it to Lee's own design. "Lee," I asked as we sat down at the chart table to go over the required paperwork, "What can you tell me about
Altitude
Basic squall thermodynamics: The temperature profile of the air mass determines the vertical stability for moist or dry air.
Temperature
dealing with squalls?" "Squalls sail on starboard tack," she shrugged. "Except, like, when they don't." "That's not much help," I said as I cleared a pile of tools from the chart table lid so that I could open it without spilling them off the table. "You need to read Will Oxley's book, Modern Race Navigation," she continued. "Is it a good squall tutorial?"
All you really need to know is that upper air, compared to the surface wind direction, is deflected to the right. "No, but it explains why you shouldn't have a chart table with an opening lid and storage inside," she said. "Actually, the book is sort of a detailed user guide to Expedition. Only available as an e-book, but a must-read for anyone navigating their first major ocean race." "I'll check it out," I assured her. "Now where did the owner put that folder with the liferaft certifications...?" Lee had a good point about the chart table. It was full of the crew's wallets and key rings, last year's tide tables, plotting instruments that we never use, a rusty splicing fid, spare batteries of unknown condition, a few almost-empty rolls of sail repair tape, a single wool sock, a big crescent wrench, and a soggy paperback novel that appeared to be about young women surviving a simultaneous storm at sea and a shark attack in a liferaft while wearing almost no clothing. At least, that's what the cover art seemed to indicate. "None of the stuff in here has anything to do with the navigator's job," Lee pointed out, "and every time someone needs something it will interrupt your work." I finally located the folder with the raft info, and asked Lee again about squall strategy and why I needed to know that the squalls usually sail on starboard tack. "Upper air follows the isobars because the coriolis forces are so strong," she said. "Surface wind is slowed by friction, so it deflects in the direction of the pressure gradient from high pressure to low pressure. But,
like, all you really need to know is that upper air, compared to the surface wind direction, is deflected to the right. So the squalls, moving mainly with the upper air, are also deflected to the right, and blow downwind as if they are sailing on a starboard tack broad reach, typically about 165 degrees off the true wind."
"H
ow do I use this info?" I asked. "Simple. If you want to get out of a squall you're in, or into a squall when you're out of one, or out of a clear spot between cloud streets with not much wind, jibe to port. You'll be on the opposite tack from the squalls. Port tack is for change. Starboard tack is for status quo." "Finally," I said. "That's the level of simplicity I need." "It gets worse," she warned. "But first you have to understand how a squall works." "Okay," I said cautiously. "I know it's driven by vertically unstable air." "But do you know why the air is unstable?" she asked. And before I could answer, we were in thermodynamics class. "Let's say you have a cubic meter of air, and you push it up a thousand meters," Lee began. "Pressure drops by about 11%, to 89% of sea level pressure. What happens to the volume of this chunk of air?" "Even I can remember this from school," I said. "The gas law states that P V equals N R T. N is the number of molecules of the gas, R is a constant, so Squalls sail on starboard tack, usually broad reaching at about 165 degree true wind angle (in the Northern Hemisphere trade winds).
