NAVIGATION for HOBART
Hobart-winning navigator and world-record-breaking sailor Adrienne Cahalan reports on what it takes to win the blue-water classic.
The great race south is on again and it is time to either dust off the race files that were kept from previous years or open a new one if it is your first race navigating. For me, the 2006 race will be my 16th race and it was race 15 before I was on the winning overall crew on corrected time.
It takes plenty of perseverance, preparation and a little bit of luck. Every year, navigators face new challenges with weather, new information sources and new technology used for navigation so it is important to make sure you give yourself the best chance you can before you leave the dock by keeping up to date. I think it is always important to approach the race each year with a clean slate, an open mind and renewed or new enthusiasm and to go back to basics and brush up on the main climatic features of the race course.
The start is situated near latitude 33° 51 S and the finish at near latitude 43°S which places the course north-south across the transition of the sub-tro
The most useful thing you can do in terms of strategy for this race is to set up a weather schedule on a 24-hour timescale of voice, weatherfax and internet updates noting in the forecast times and areas and when each new analysis, observation data set or model run is issued. In addition, whether you are a big or small boat, it is important to try to have some access to the internet for two reasons, namely, the type of weather information you will get is a real edge and knowing where your competitors are at the 10-minute intervals given by the race website is critical. A laptop and mobile phone is good but coverage will be limited so if you can afford CDMA or satellite phone like Globalstar it may be worth the investment.
Tactically, I see three main points for decision-making to get to Tasman Light first whether you are navigating a big or small boat: the NSW coast, Bass Strait, and the Tasmanian coast including the approach to Tasman Light. The three gates are pivotal because of their geographic features relating to currents and weather and are roughly all about 150-200nautical miles apart in length which is between three-quarters to one day, depending on the size of the boat. The first part of the race is often characterised by NE sea breezes along the NSW coast. If you are sailing in a sea breeze, the first key decision is where to maximise gains from current versus staying in the optimum wind speed and direction. Knowing the current speed and direction at waypoints from the coast out past the continental shelf is critical in order to make the best decision where to maximise current gains. Should you chase the current to its location offshore straight away or just meet it closer to rhumb line, usually somewhere near Jervis Bay? The East Australian Current (EAC) can run down the coast at speeds of up to 3-4 knots normally just close to and offshore of the continental shelf, so if you are a smaller boat this is an important strategic consideration. For the bigger boats over say 50-60ft where the speed of the current is a lower relative percentage of the overall boat speed, especially downwind, it is less of a consideration. For any boat, it is important to study the EAC eddies on the course that may put a boat in adverse current – something to be very careful of.
Regard to safety and equipment is also important in relation to current. The EAC has its origin in the Coral Sea off north-east Australia, so the current brings very warm waters of up to 26C to the area where the race takes place. So if a front is forecast, as a small boat, you want to make sure that you are happy to be out in a strong south-running current because if a south wind blows, the seas out there will get very steep. This first section along the NSW coast is also where good preparation in terms of instruments really comes into its own. Knowledge of your yacht?s performance at every wind speed and angle is critical to every tactical decision, together with accurate calibration of sea temperature, barometer, wind speed/direction and boat speed. Calibration is an area that is often left to the last minute and as a result quite often not done at all. However, you are wasting your time thinking you can really know where you are relative to weather and current on the course if your instruments are not calibrated properly.
NSW coast and Bass Strait
On the NSW coast, if you are lucky you will gybe your way down to Gabo Island. However, it is not unusual to have a front from the SW cross the course on the first night or the morning of the 27th. Therefore, the second key decision relates to the timing of the first front from the south and how to set yourself up for it and Bass Strait. These fronts may bring strong SW headwinds as you enter Bass Strait. This is where the yachts having access to the internet have a distinct advantage. Knowing where the front is by monitoring observations put out by the coastal stations every hour give you a solid base of information to plan where to set yourself up for the approaching front. You can then determine accurately when, for example, to take the last gybe back into the shore if you do not want to get caught too far offshore without wasting any time or to just give the right notice to the crew on deck when to expect to reef or change sails.
The second part of the race across Bass Strait most often is sailed in some type of west sector wind associated with a mid-latitude low. One of the most important things to know in this part of the race is where the centre of that low is, how strong the winds will be, where it will pass in relation to the race course and if any troughs associated with it will affect which side of the rhumb line you want to be on as you approach the coast of Tasmania. Will the wind be SSW, SW or WSW? Will it shift quickly or stay the same direction? It is often a decision whether to sail faster and a little off the wind rather than dead upwind in the anticipation that the wind may move slowly aft or just sail straight at the mark.
The Sydney-Hobart is an endurance race for smaller boats and a sprint race for the larger ones, but a navigator should always make sure that they position their boat where they can recover from any bad tactical decision or bad weather. I am conservative so I always plan for best case and worst case scenarios both tactically and in times of forecast of bad weather so that I can readjust the strategy should a weather situation not play out quite as expected. A navigator must race to win but must also keep in the back of his or her mind that it is also their role to keep the boat in safe weather and seas.
Tasmanian coast
After Bass Strait, the third key decision point is to have a plan as to how you will approach Tasman Light. If it is a SW, should you stay offshore or inshore? How quickly will the wind rotate into east sector winds after a front or how far offshore should I be for making the best use of the afternoon sea breezes on the Tasmanian coast? The Tasmanian coast has high land which makes this section of the course particularly challenging. There is a definite trick to staying just the right amount off the Tasmanian coast in order not to get stopped in the lee of the high land in light airs. When sea breezes are forecast on this coast you have to be very careful not to get caught in the subsiding air offshore, the result of which will see yachts pass on either side of you; either in gradient wind to the east or sea breeze to the west. Try to find out in advance the optimum distance offshore to be based on the forecast in a sea breeze situation and in the race. Using a combination of synoptic charts and local coastal reports will always give you a good feel for how much wind there will be across the course. It is always important to check the coast stations before the race and know in advance at what times and in which wind directions information from these coastal stations can be unreliable.
When you get to Tasman Light you will know how well you went with your ?ocean strategic decision-making? and that?s it. Yet, although the final leg from Tasman Light to the finish is a direct route through Storm Bay to the finish and often you get what you get through there, there are still plenty of decisions to be made about how to get to the finish as quickly as possible. By that stage you have fewer options to pass or be passed unless you are one of the lucky or unlucky ones whose passage coincides with a decrease in wind (usually overnight) and you either sail up to the fleet in front or the fleet sails up behind or around you. The final miles from Tasman Light into Hobart can be soul-destroying and unfair, but damage can be minimised by knowing when and where to avoid adverse tide (up to 2kts) on the Derwent River and where to position yourself for the forecast new wind to get to it first if the wind dies.
Winning the Hobart race will always be a trade off between sailing fast and keeping the boat and crew in one piece. The decision to back off is always a hard one, based largely on the preparation of the yacht and the experience of the crew. However planning strategy and analysing potential forecasts in advance will go a long way to making any decisions on the water significantly better informed. One key to the race is planning in advance different weather strategy scenarios before you leave the dock. Then agreeing among the skipper or tacticians a plan for that situation, so that when you are out in the heat of the race you have few surprises, disagreements and discussion is kept to a minimum. This leaves you free to just get on with it!
