Tuesday, June 26, 2007

Ghosting Along

Hope some of our NOAA friends are watching. We are at Latitude 33N40 and sliding along a ridge that extends eastward out of a high pressure area towards Los Angles, which is our goal. We are 666 miles out and have been on this ridge for days. The GRIB charts we have been consulting show good solid winds from the north increasing from 5-10, 10-15, maybe even 20 knots as we move toward the mainland. The reality is 3-5 knots and sometimes nothing at all for extended periods. Our GPS has a feature that predicts our time of arrival based on the distance and our boat speed. it is a little discouraging to sit here and note that after each hour the arrival time has receded two hours. Of course, the worst example of this phenomenon occurred on the second day of the 1998 Pacific Cup race. On that occasion the GPS predicted that we were likely to cross the finish line in Hawaii on Christmas Day.

It is Tuesday, 26 June 2007, 0600 HST, and it feels like Long Beach is just over the horizon. Actually, we are at 33N37, 131W35 and our course is 090M, speed 3 knots. True wind is about 300M, 3-4 knots.

Lacking anything better to do with my time let me give a little lecture about relative and true wind. Yesterday we made the interesting observation that the boat speed was 6, the relative wind was 6 and the true wind that we had calculated was also 6. Here is how it works. The true wind was actually hitting the boat 60 degrees from aft on the port side. That's 30 degrees "abaft the beam" for you sailor types. The 6 knot forward motion of the boat that resulted created a wind that appeared to move the apparent wind direction forward so that the wind appeared to be coming from 30 degrees ahead of the beam on the port side. The wind vectors formed a perfect isosceles triangle where an extension of the port beam would be a symmetry axis for the triangle.

Cirrus is great in light air, but there is a limit.

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