Transpac Weather & Tactics
By Stan Honey
Stan Honey has navigated in nineteen transpacific races and has won eight times. As navigator, Stan holds both the single-handed, double-handed, Pacific Cup and Transpac records for mono-hulls to Hawaii.
General Considerations: overall race structure & necessary decisions
The primary feature dominating the Transpac 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 of sailing the race 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 Transpacs where yachts 10 miles to the south of their competitors have experienced 1 knot more wind. A sled in those conditions can sail a 1/2-knot faster and would therefore gain 12 miles per day on their northern competitors. This condition can persist for the entire middle-third of the race and can eliminate any chance of recovery for the yachts positioned too far north. 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. This condition, dominates the results of most Transpacs.
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, they will also 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 cash-in the southing to reach up in front of the northern boats because everyone is reaching fast.
The Start and Beat to the West End of Catalina
Generally, boats should tack up the Palos Verdes coastline from the start until the Westerly has filled in and they can at least lay Catalina's isthmus. When they tack onto starboard to cross the channel, they should continue all the way across, and not tack in mid-channel. There is substantial adverse current and lighter wind in mid-channel and it is better to get right across into the accelerated wind and reduced current off Catalina.
Transpac's Three Sections
It is helpful to think of the Transpac as having three sections: the windy reach to the Pacific High's ridge; the "slot cars" section in the middle; and finally, the run to the finish. The Pacific High nearly always has a ridge extending off its southeast corner, which is visible on a weather map as a U-shape of the isobars. After rounding Catalina's west end, yachts have a windy reach for a couple of days, depending on their speed. When they get to that ridge, the wind lightens up and veers very quickly. You will find that after reaching in lots of wind for 2 days, when you finally get the spinnaker up and are struggling to carry it, within 6 hours or so the pole is back and you’re running on your downwind polars in much lighter air; you just crossed the ridge.
The most critical decision of the Transpac race is where to cross the ridge, because once a boat gets to it and the wind veers, it cannot get farther south. It is already sailing as low as it can on its polars and it cannot jibe without a huge penalty. This is why the middle of the race is called slot cars.
The middle-third of the race begins as soon as you cross the ridge and the spinnaker pole comes aft. Throughout this part of the race, everyone sails as low as they can, e.g., sails their downwind polars. Back at the west end of Catalina the decision was made as to where to cross the ridge, and all must live with that decision for the next three days or so.
If a boat is too far north, the yachts will slowly outdistance it to the south and there is nothing that can be done. If it is even further north, all on board will experience unbelievable torture, for as the wind gets lighter, the boat's polars will force it to be sailed higher and higher, until it "spins out" up into the high. When it is eventually jibed to avoid starvation, the angle on port pole has the boat heading due south, far behind the competitors' transoms.
The "slot cars" leg ends when the wind eventually veers far enough so that both jibes are symmetrical along the course to the finish and the yachts can sail either jibe.
The final 1/3rd of the race is “the run”. This is why we sail Transpacs. The wind picks up as you approach the islands and you are surfing the trade wind swells.
Generally, the right hand side of the course is favored during the run because the wind slowly veers as boats sail further west. The wind speed evens across the course in the final third of the race. The best course is to favor starboard pole until the last jibe to the vicinity of the Islands, and then come in on port pole to approach Molokai at Kalaupapa. Be sure to account for the fact that the wind will continue to veer, and do not over-stand Kalaupapa. Oddly, those boats that get too far north in the middle of the race and stew about it for 3-4 days jibe onto port as soon as they can and sail to the south after there is no longer a wind-speed advantage. These boats then miss the right shift in the last 1/3rd of the race and lose even more.
Special Consideration - Squalls
In contrast to popular perception, squalls do not work the way "catspaws" do. Catspaws have diverging wind in front of them, whereas trade wind squalls have converging winds at their leading edge. The wind converges because there is an updraft in front of a squall. Also, the average wind in a squall is veered about 15 degrees to the right of the path of the prevailing surface wind and the squall itself moves about 15 degrees to the right of the path of the surface wind. Behind a squall the wind is light, particularly near dawn.
In general, heavy boats should jibe to port pole as a squall approaches, stay on port pole right through the squall, and then jibe back when the squall has passed completely over and wind speed and angle has returned to the prevailing conditions. To jibe back to starboard pole too early risks crossing behind the squall and getting into the light air in its wake.
Light, fast boats should jibe in front of any squall within reach and then jibe back and forth in front of the squall for as long as possible. Each jibe "back" towards the squall will be at a horrible angle because of the way the wind toes-in in front of the squall, but it should still be done as the boat's velocity makes up for the angle. When the squall finally passes, again boats should exit on port pole and get away from it to avoid getting becalmed behind it. 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. Port pole allows them to diverge rapidly from the light air behind the squall.
Approaching the Finish
Pick your approach to come into Molokai at Kalaupapa on port pole. Jibe close to Kalaupapa and sail as low as possible on starboard pole along Molokai in the accelerated wind. When they get to the west end of Molokai, if they have been lifted away from shore, they must jibe back on port to get close to Ilio Point where there is accelerated wind. At that point, they should jibe onto starboard and cross the channel to Oahu.
Oahu should never be approached much above Koko Head, but it is fine to sail close to Koko Head and then straight for the finish off Diamond Head. As boats approach the finish line, they should plot their track on the chart and take GPS fixes as well as periodic bearings with a hand-bearing compass. The finish line is deceptive and many yachts get too close to shore when they cannot see the red buoy. The best technique is to plot the course and navigate to the buoy, rather than expect to see it. With spectator boats around, the buoy often cannot be seen until it is within 100 yards.
When to Break the Rules
Although all of the above information is relevant to a typical Transpac, there are unusual races in which the rules must be broken. To know when, crews must pay attention to their boat's polars. If they are on a sled, it is worth sailing extra miles to get extra wind because, no matter how hard it blows, the boat will go faster if it gets more wind.
On the other hand, if the boat is of moderate displacement, it should not be sailed extra miles for any more wind than necessary to reach hull speed. If it is sailed farther to get even more wind, the crew will have more fun, but their average speed won't increase enough to pay for the extra distance.
Crews should also watch for tropical depressions. Their inverted troughs that extend north can cause the trade wind direction to shift from normal and can make a huge difference in picking an approach to the Islands.
Weather Information
The best source of information about the future position and strength of the high comes from the 500mb prognostic charts, but they can take some practice to interpret. Zonal flow, or a straight E-W path of the jetstream is characteristic of southerly and weaker surface high. A jetstream with a large (omega shaped) wave is characteristic of a strong high. The next best source is the surface prognostic charts. Satellite imagery via NOAA is fun, but not really much use in a race in the tropics other than to monitor the position of tropical depressions.
The following are links to weather services that will give a good indication of the weather conditions:
http://www.oceanweather.com/data/ Under “current marine data” click on the Hawaiian Islands and this site gives a simple graphic representation of wind, waves & water temperature for the North Pacific.
(Cloud cover) http://www.ssd.noaa.gov/goes/west/nepac/vis-l.jpg
(Hawaiian Islands cloud cover) http://www.ssd.noaa.gov/goes/west/hi/vis-l.jpg
The finish line is just off Diamond Head on Oahu and roughly 21°N 157°W
Author’s Disclaimers
All of the above comments are relevant to typical Transpacs. 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 sled, it is worth sailing extra miles to get extra wind, because no matter how hard it blows, a sled will sail still faster if you get more wind. On the other hand, if you are racing a moderate 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 won’t 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.
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