tide over


This will be the fifth year that Tidetech has supported the Rolex Sydney Hobart race with tactical oceanographic data. In every Sydney Hobart since 2008, the handicap winners used Tidetech’s data. Last year Investec Loyal, a Tidetech subscriber with Stan Honey aboard as navigator, pipped Wild Oats XI for Line Honours. Investec Loyal went east  (track, pictured left)for fresh breeze and favourable current in 2011. It worked!

This year, the offshore currents for the Rolex Sydney Hobart are shaping-up to be potentially volatile and the fleet may face complexities that could profoundly affect the outcome of the race.


In the last two years the East Australian Current (EAC) has been reasonably straightforward, as these things go. The assumption for many years has been that a Hobart-bound yacht need only sail out through Sydney Heads, find the 200m contour, turn right and ride the EAC as far south as Eden at least. Often between Sydney and Batemans Bay there is little current of note, then increasing southbound flow between Ulladulla and Green Cape. The last two years has also seen a fairly consistent eddy sitting off Green Cape that has helped some vessels with a positive slingshot effect. Yet in 2009 it paid to head a lot further east before turning south for Hobart – that year, the boat that went furthest east (Two True – a Beneteau First 40) gained a significant benefit from the southbound current and won the race overall.


Recent information recorded from 4-12 December has raised the spectre of the race not being ‘business as usual’ in 2012… We’re very lucky at the moment to have a NOAA floating measurement buoy drifting in and around the waters of the EAC. We’ve been paying close attention to its data feed over the last few weeks and, significantly, the buoy spent several days heading north in this ‘reliable’ current. 4-12 December demonstrated the complexity of the water movement and we also saw a volatile system of eddies in the EAC between Batemen’s Bay and the Bass Strait, one of the reasons we saw the north-bound current during that time. The unpredictable nature of these eddies could make the race more complicated tactically – the prospect of meeting northbound current on the ‘usual’ track doesn’t make for pleasant viewing.


According to the Australian government report  ‘Marine Climate Change in Australia – impacts and adaptation responses. 2009 REPORT CARD’ – compiled by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and the National Climate Change Adaptation Research Facility (NCCARF) – the flow of the East Australian Current has strengthened, and is likely to strengthen by a further 20% by 2100. “Southward flow has strengthened so warmer, saltier water is now found 350 km further south compared to 60 years ago (HIGH confidence) “[The EAC is] likely to strengthen by a further 20% by 2100 (MEDIUM confidence)”


On Wednesday 19 December there was a sequence of six eddies that could affect the racecourse with varying influence on tactics and overall optimised route strategy.Caption: Wednesday 19 December 2012 – six fast changing eddies that could influence tactics during 2012 Rolex Sydney Hobart Looking back and comparing to Monday 17 December it’s clear that these rotations are changing quickly and could have a profound influence on a yacht that gets caught in the wrong place at the wrong time. C


Last year’s Line Honours winner Investec Loyal chose to head slightly further east in its Bass Strait crossing. This was nominally to gain the benefit of new wind filling from the east after a significant drop-off in pressure; it also allowed them to use the current more effectively. Investec’s 2011 navigator Stan Honey sent us the track Investec took across the Bass Strait – the red arrows show the current as an actual measurement. The combination of fresh breeze and favourable current could well have been the three-minute difference that gave Loyal its maiden Rolex Sydney Hobart Line Honours.


The difficulties of the Hobart approaches and the Derwent River (graph, left) have made and broken many a Sydney Hobart campaign. There are several elements that can change the conditions quite dramatically, none of them obvious – wind can die after sunset; an often strong outflow from the Derwent River can have a huge effect (particularly after rain) by mixing with the tidal flow to make current patterns complex and unpredictable; river flow often stays in a narrow band all the way out to the Tasman Peninsular, enhanced by the ebb tide.
Caption: It all hangs on Hobart. Overall, It’s tricky. Read more on the complexities of the final stretch to the line in this article.


Tidetech has set up its 2013 packages for the race. Subscribers can choose from full GRIB files to download and use in tactical navigation software (including Sydney and Hobart tides; ocean currents; new, updated sea surface temperatures; and wave height, length, speed and direction forecasts) or Tidetech’s exclusive OceanView online viewer and PDF generator. The packages also include access to an online video briefing from Tidetech’s leading science and navigation team. Click here to find out more . Tidetech’s GRIB packages can be accessed within Adrena and Expedition navigation software applications. Click here for Tidetech’s Expedition support page . Tidetech is a technical supplier to the 34th America’s Cup and supplied the 2011-12 Volvo Ocean Race.