June 13, 2024 - Quantum Sails
There are four components that factor into a tactician’s strategic guesses: predicted weather, current, local knowledge, and observed conditions. Of the four, one and three have the least value. While of more impact in distance racing strategy, weather reports generally are thought to be relatively useless in short course racing. Local knowledge is a two-edged sword that often bites back. Quantum Annapolis’ Dave Flynn looks at each and see how they might factor into a strategic plan. This piece was originally published in Spinsheet Magazine, May 2024.
WEATHER
The only thing wind models like the GFS or HRRR, NOAA weather, the weather channel, and newspaper or TV reports make you sure of is that there will be weather. Each suffers from two problems. First, they cover too large an area to tell us what is going to happen in a two-mile rectangle. The second is timing. In general, most weather sources are correct about the overall trends and conditions. They falter when it comes to when. They just can’t tell you what will happen in the one to two hours that it takes to sail a race.
There is a better source for the kind of information the tactician needs, private weather forecasting. Standard issue information at the top levels of the sport, they cost roughly fifty dollars a day (the cost of the lunches). You get a race area specific forecast, with actual wind directions and velocities, and predicted timing of shifts, written in the language of the tactician. It comes with a big picture overview, an overall degree of confidence rating, and things to look for (like developing thermal clouds) which may be signs that one trend or the other will be more likely to materialize.
This is still not to say that one should make tactical decisions based on forecasting. Observed conditions rule. Even private forecasts usually cannot speak to pressure (velocity) differences across the course. In light air, (particularly downwind), it is pressure more than shifts that counts. But the tactician is trying to put together a puzzle, and all clues, even a prediction that proves false, can help. If observed conditions happen to match the forecast, voila! You can have a much higher level of confidence that you are doing the right thing. Conditions don’t match, then stop trying to guess and stay with the fleet. You will find top tacticians comparing the predictions of two or three private services in the search for patterns.
With these disclaimers in mind, let’s look at a sample predicted forecast. This is for a Screw Pile event day one (a classic Chesapeake Bay regatta) and it is from Commander’s Weather Service, one of the very best private services. The report is from Saturday morning. The Sunday morning update (forecasts are typically updated each morning before the race) will obviously be more reliable.
Summary Sunday, July 181) High pressure will still be in control2) Cold front will move to northern Maine and then extend to near Buffalo and SW from there3) Should have a little more gradient tomorrow, so wind speeds should be a bit higher4) Will go with a SW to SSW breeze of 4-8 knots early, increasing to 9-13 in the afternoon0900 230-250 5-91100 210-230 7-111300 200-220 8-121500 200-220 9-131700 210-230 10-14
Error Factor1) Max left of 240 from mid-morning on while max right will be 1602) Most likely range is 180-2103) Think stronger pressure will come from S or SSE (170-190) while lighter air will tend to be more 200-2204) Could see sea breeze fall off to under 5 kts. at times 11am-1pm
Sounds like a classic Chesapeake Bay day. Building sea breeze (thermal). Early pressure advantage to the left (stronger pressure 170-190). Breeze slightly further right as the day goes on and things stabilize. Based on this information tactician would be looking to favor the left side of the beat early but becoming less concerned later in the day and watching out for a shift to the right. On the run staying in better pressure would be principal concern so extending on starboard after the top mark rounding and staying right (looking downwind) on the run would be the play. Later in the day an early jibe would still not be the right move. Better to sail away from the shift and then jibe back onto the headed port jibe once the right shift came through. In general, however, less importance to which jibe to pick as the breeze built and conditions stabilized. Anything with clear air is fine.
CURRENT
Current is the next factor unless you are lucky enough to sail on the Great Lakes. If we know the direction, we want to stay in max current when it is with us and get out of if it is against us. Simple! We also know that deeper water means more current and shallower water less. Go deep when current is with and shallow when against. Finally we know that current turns first in shallower water. Current tables are key. Not just high and low but more importantly maximum ebb or flood times. In areas like San Francisco Bay tide tables are nearly 100% reliable. In places like the Chesapeake Bay not so much. The relatively shallow waters and small tidal range of the Bay means that sometimes reality does not match predictions. In a strong northerly for example the current may never really flow in (north against the wind) significantly but will go out the Bay (south) all day. Observed conditions (more on this shortly) are the key. Check current on buoys at various parts of the course area to see what is really going on. The tricky part for the tactician is when the wind direction/pressure say to go one way and the current says the other. In our mid-Bay Screw Pile Regatta example where we wanted to go left on the beat early for better pressure, what if the current was coming in? This would put it against us on the beat and water is deeper to the left (that is where the shipping channel is). Those are the tough ones. Generally speaking the lighter the air, the more important current becomes but it is all relative. We also want to stay in best pressure in the light stuff. A little more wind goes a long way for boat speed. This is where the tactician earns their keep.
LOCAL KNOWLEDGE
This is the one I always have the least faith in. However, I do make notes every time I go to a regatta about the conditions and what works. There are examples of clearly repeatable situations that you need to keep a look out for. Sailing in Annapolis in a northerly breeze is a good example. It is dependent on where the racecourse is setup which typically for bigger fleets means out in the Bay. The rule of thumb is that if starboard tack upwind takes you toward the western shoreline it will pay to go left. There are a couple of other factors influencing this decision. If the current is going out (typical in a northerly even if the tables say otherwise) the water is shallower to the left so current relief is available. Also, as we approach the shoreline there is often a geographical shift to the left due to the influence of land. I would not take this “go left on the beat” strategy to the bank, but I have seen it enough times to follow it if no other clues said otherwise. Local knowledge is most powerful in more confined bodies of water where land is involved.
OBSERVED CONDITIONS
For the tactician, this is the gold standard. “In God we trust. All others bring data.” This is why it is critical to get out early before a race. The normal rule is one hour of sailing prior to the start. This is time to practice tacks, jibes, sets, douses, and get the tuning and trim setups. At the same time make current observations on marks and buoys. Are the tables lining up? Does there seem to be current on one side or the other? It is also time to log what the wind is really doing. If you are on a bigger boat with high end instruments that are well calibrated, you can log the true wind direction and wind speed and spit out a graph. This is almost like cheating. For mortals who may not have the best calibrated systems there is the old standby, compass headings. No matter what you are sailing log upwind and downwind port and starboard compass headings. Doing the basic math will give you the true wind direction. You can also always remember the old adage “port higher header.” If the compass numbers are getting bigger on port you are being headed. Smaller numbers lifted. Starboard tack is opposite.
Knowing compass headings gives you instant understanding of what the wind direction is doing so you can compare to weather predictions and local knowledge inputs. You can also log wind speed but usually just sailing up the course will give you a good feel for where there is more or less pressure. If you know what the breeze direction is doing the strategic rules are straight forward. If you do not you are simply guessing. Finally, it you have a tuning partner with similar speed you can (after tuning up for speed settings) split sides of the beat or run and see who comes out in front. Simple, empirical, but effective. In an ideal world we would like to sail a complete beat and run before the start to gather the data we will need.
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