Weather and Course Selection

Straight line from San Francisco to Hawaii does not work. Almost ever. Here is how to figure out what to do.

Offshore weather resources, in a nutshell

Course Outline by Jim Corenman

1. Look Outdoors

a. Calibrated barometer/barograph

b. Wind speed and direction

c. Cloud observations

2. Warnings and text forecasts (general info: http://www.nws.noaa.gov/om/marine/home.htm)

a. Via HF SSB (voice) from USCG http://www.nws.noaa.gov/om/marine/hfvoice.htm

b. Via HF SITOR (radiotelex) from USCG http://www.nws.noaa.gov/om/marine/hfsitor.htm

c. Via email from Saildocs (email: info@saildocs.com)

d. Via sat-phone/Internet http://www.nws.noaa.gov/om/marine/forecast.htm

3. Radiofax charts via HF-SSB http://weather.noaa.gov/fax/marine.shtml

4. Forecast data in Grib format

a. Sources:

i. Saildocs (email gribinfo@saildocs.com)

ii. Global Marine Net (http://www.globalmarinenet.net/grib.htm)

iii. http://www.navcenter.com/

b. Viewers and grib-compatible chart programs:

i. Airmail/Viewfax (http://www.siriuscyber.net/wxfax)

ii. MaxSea (http://www.maxseainc.com/index.html or http://setsail.com/maxsea/intro.html)

iii. Raytech (http://www.raymarine.com)

c. How to get it

i. Sailmail (http://www.sailmail.com)

ii. Iridium (http://iridium.com)

 

Stan Honey's Weather Advice

Stan Honey has navigated in fourteen transpacific races, finishing first six times. As navigator, Stan has set the single-handed, double-handed, and fully-crewed passage records for monohulls to Hawaii. In 1996, Stan and Sally (Lindsay Honey) won the Pacific Cup overall, sailing their Cal 40 Illusion doublehanded. This year Stan will be navigating the Turbosled Pyewacket.

Overall race structure and necessary decisions

  • The primary feature that determines the tactics in a transpacific race is the Pacific High. Typically there is no wind in the center of the high, and increasing wind as you get farther south, up to a limit. The central question concerning course selection is: how close to sail to the high, or how many extra miles to sail to get farther from the high? In years when the Pacific High is weak (or weakening) and positioned well south, there can be strikingly more wind to the south. There have been transpacific races where yachts that are 10 miles to the south of competitors can experience one knot more wind. An ultra-light-displacement-maxi (sled), in one knot more wind will sail 1/2 knot faster, and therefore would gain 12 miles per day on the northern competitor. Smaller uldb's will similarly gain from the additional wind. Although the gain is less for heavier boats, it is still a significant factor. This condition can persist for the entire middle third of the race. Note that all yachts in this middle third of the race are nearly fetching the finish on starboard pole, so the boats caught too far north cannot jibe out of their predicament without sailing a dramatically unfavored angle, and passing far astern of the competitors to the south.

    Occasionally, however, the Pacific High will be strong (or strengthening), and located far to the north. In these conditions, it IS possible to be too far south. The boats that sail closer to the high will not only get more wind, but will sail the shorter distance. Typically in these sorts of years, the wind stays "reachy" throughout the middle third of the race, so the boats that paid extra distance to get south cannot even "cash in" the southing and reach up in front of the northern boats, because everyone is reaching fast.

    • The start and exit from the Bay

  • Get a comfortable start. It is senseless to risk a foul or collision at the start of a 2000 mile race, so consider starting 15 to 30 seconds late. The start is generally scheduled for an ebb tide, so this discussion will make that assumption. Tack shortly after the start, and take long tacks across the center of the bay in order to stay in the favorable current. Pass under the bridge at mid-span.

    After clearing Seal Rocks the wind velocity will reduce and the wind will begin to veer. As you free your sheets you need to work out your overall race tactics; the course that you select for the first night and the next day will determine your tactics for the rest of the race.

    • The three portions of the Pacific Cup:

  • It is helpful to think of the Pacific Cup in three sections:

    1. the windy reach to the ridge;

    2. "slotcars" through the middle third; and

    3. the run for the last third..

    The Pacific High nearly always has a ridge extending from its southeast corner. On the weather map this is visible as a "U" shape in the isobars on the southeast corner of the high. After leaving coastal waters, you will have a windy reach for a couple of days, depending on your yacht's speed, but when you get to the ridge, the wind will lighten and veer very quickly. Within 6 hours after you initially set the spinnaker, the wind will lift and you will be running on your downwind polars in much lighter air. You just crossed the ridge.

    The most critical decision of the Pacific Cup is where to cross the ridge. The reason this is critical is, once you get to the ridge and the wind comes back, you can not get farther south. It never pays to sail lower than your polars, and you can not jibe (onto the dramatically unfavored port pole) without huge penalty. That is why the middle third of the race is called "slotcars."

    As you left the coast you made your decision where you wanted to cross the ridge, you sailed there, and now you have to live with it for four or five days. If you are too far to the north, you will be slowly destroyed by the yachts to the south of you, and there is nothing that you can do about it; you cannot jibe (without huge penalty), and you should not sail lower than your polars. If you are substantially too far north, you will experience torture. As the wind gets lighter, your polars force you to sail higher and higher, until you "spin out" up into the high. If you have to jibe to avoid total calm, your angle on port pole will have you heading due south, far behind your competitor's transoms. The "slotcars" leg ends when the wind eventually veers far enough so that both jibes are symmetrical around the course to the finish, allowing you to sail either jibe.

    The final third of the race is "the run." This is why we sail Pacific Cups. The wind picks up as you approach the Islands, and you get to practice your helmsmanship surfing tradewind swells. Generally the right hand side of the course is favored in the final third of the race, because the wind slowly veers as you sail west.

    In the final third of the race the wind speed is generally even across the course. Oddly, the boats that get too far north in the middle of the race, and stew about it for 3-4 days, often jibe onto port as soon as they can, sailing to the south when there is no longer a windspeed advantage. These boats then miss the right shift in the last third of the race and lose even more.

    • Instead, favor starboard pole until you can nearly lay the Islands, and then approach Oahu on port pole. Be sure to account for the fact that the wind will continue to veer, and do not overstand Kaneohe. One way to avoid overstanding is to plot a waypoint that is 60-100 miles directly upwind of the finish and jibe onto port pole when you can lay that waypoint. The wind will continue to shift to the right, so that when you actually cross the line that is upwind of the finish you may find that you are substantially closer to Kaneohe than your initial waypoint.


    Approaching the Finish

  • Arrange your final jibe or two so that you pass 10 miles due upwind of the finish. Then sail half the remaining distance on starboard pole, and then make your final 5 mile approach on port pole. As you approach the finish, plot your track on the chart, and take GPS fixes as well as periodic bearings with your hand bearing compass. The finish buoy is hard to see. The best technique is to plot your position and navigate to the finish, rather than expect to see the buoy. It's not even worth looking for the buoy until you navigate to within about one half mile of it.

    In the daytime, take bearings on:

  • Makapuu (the left edge of Oahu)

    Mokapu (the turtle's head)

    the giant ping pong balls near Pyramid Rock (labeled "radomes" on chart)

    Pyramid Rock (white house with diagonal stripes on conical rock)

    • At night, take bearings on:

  • Molokai light, range 28 miles, loom visible 60 miles (flashing 10s)

    Makapuu light (occulting 10s)

    Marine AeroBeacon, sometimes obscured (alt green/white or red/white)

    Pyramid Light (occulting 4s)

    (if you don't know what "occulting" means then refresh your coastal piloting skills)

    • Remember that the reef is only 0.8 miles beyond the finish line, so douse your spinnaker promptly. If for some reason you have trouble dousing your spinnaker, jibe onto starboard and sheet your mainsail hard. If you can maintain a beam reach, even with the kite flogging in the rigging, you will stay clear of the reef.

    Squalls

  • Typically, you will get tradewind squalls for the last three or four nights of the race. They only occur at night, starting about midnight and continuing and strengthening until dawn. If there is a moon, the squalls are visible for miles because of their incredible height. If there is no moon, you can often detect squalls behind you by watching for the absence of stars. If you have radar, squalls are easily detectable. Each squall on a given night will behave almost exactly like its predecessor, except it will be a little stronger. So "go to school" on each squall in order to sort out how to best take advantage of the next one. If one squall provided more fun than you really wanted, douse the kite and wing out a jib for the next one. If a squall is approaching, and you get rain before the wind, prepare for lots of wind. At dawn the squalls vanish, but leave calm zones around and particularly behind them. These calm zones are worth taking great care to avoid.

    The comments below assume normal right shifting squalls. Occasionally there will be a night of squalls with no wind shifts in them, or even with left shifts. The following characterizations are very typical, but the best prediction of what you will experience in a squall is the experience you had in the previous squall the same night.

    In contrast to popular perception, squalls do not generally work the way "catspaws" do. Catspaws have diverging wind in front of them. Surprisingly, tradewind squalls often have converging winds at their leading edge. The wind converges because there is an updraft in front of the squall. In addition, the average wind in the squall is generally veered about 15 degrees or so to the right of the prevailing surface wind, and the squall itself moves about 15 degrees to the right of the path of the surface wind. Behind squalls the wind is light, particularly near dawn.

    If you want to race aggressively, watch for squalls and jibe to get in front of them. As they overtake you, jibe to port pole. Stay on port pole during the squall, sailing as deep as you dare, and then jibe back to starboard only when the squall has passed completely over you and your wind speed and angle have returned to the prevailing conditions. If you jibe back to starboard pole too early, you run the risk of crossing behind the squall and getting into the light air in the wake of the squall. If you have the good fortune to be sailing on a sled, you can sail fast enough to stay in the accelerated wind in front of the squall for hours. This requires jibing back and forth in front of the squall, jibing about every 15 minutes. Each jibe "back" towards the squall will be at a horrible angle, because of the way that the wind "toes in" in front of the squall, but jibe back anyway. The additional wind velocity in front of the squall makes up for the horrible angle. If you are racing aggressively, you will jibe over 50 times in a Pacific Cup, with most jibes taking place at night in squalls.

    Port pole is more effective to avoid the calm behind a squall because the squall itself is moving to the right of the path of the surface wind, so port pole allows you to diverge rapidly from the light air area behind the squall. It is perilous to exit a squall on starboard pole because of the risk of getting becalmed behind the squall, particularly near dawn.

    • Weather Information

  • The best source of information about the future position and strength of the high comes from the 500 mb progs via weatherfax. Interpreting upper level charts is beyond the scope of this article, but various colleges have Meteorology courses. The next best sources of data are the surface analysis and surface progs which are also available via weatherfax. Satellite imagery via NOAA APT satellites is fun, but not really essential for a race in the tradewinds. Save this system for use in middle and high latitudes where there are lows and cold fronts to observe.

    • Author's Disclaimers

  • All of the above comments are relevant to typical Pacific Cups. There are unusual races in which you have to break the above rules to win.

    Pay attention to your boat's polars. If you are racing a light displacement boat, it is worth sailing extra miles to get extra wind, because no matter how hard it blows, a light boat will sail still faster if you get more wind. On the other hand, if you are racing a heavy displacement boat, do not sail any extra miles in order to get more wind than necessary to reach hull speed. If you sail farther to get more wind, you will have more fun, but your average speed will not increase enough to pay for the extra distance.

    Watch for tropical depressions. The inverted troughs that extend north of a tropical depression can cause the tradewind direction to shift from normal. This can make a huge difference as you are picking your approach to the Islands.

    • Finally

  • Pick your strategy, and stick to it. Then whatever happens, make up your story for the bar in Kaneohe, and stick to it.