DRAKE PASSAGE AND THE CHALLENGE OF CROSSING       The Drake passage is one of the most notorious stretches of water in any ocean. Almost 500 miles wide, it separates The South American sub continent from the Antarctic peninsula. Since it's discovery by Sir Francis Drake on his circumnavigation in the 16th century, it has claimed many vessels. The Stormy waters off Cape Horn are feared and respected by all.       When Northanger left for Antarctica in February 2003, one of the aims of the expedition was to have no surprises with the weather and to get to and from Antarctica comfortably. While this is the aim of all sailors, Northanger went about a little more aggressively and took on board a formidable array of tools to make this happen.       My job was to make this all happen. I am a programmer for SkyEye Systems ltd. and also an avid sailor. Part of the success of the software is that I test out my software and concepts at sea. The core of this arsenal was the SkyEye weather satellite receiver. SkyEye tracks American weather satellites and taps into the video channel when the satellite is in view allowing live pictures of the area to be downloaded day and night. It is rather like having a personal camera mounted on top of a 400 mile high mountain.       The other item on the list is the huge resources of NOAA's weather prediction modeling computer bank. There are several models out there. Northanger used the ocean wave prediction model (WWAVE3).       I have been working with Dr Luis Soltero of Global Marine Networks LLC. Together we have been bring this technology down to earth. I first started using this technology with my copy of MaxSea – an electronic charting package I was given to evaluate. The data provided by MaxSea's Navcenter.com website was of uncanny accuracy when I started evaluating it. I was also evaluating SailDocs.com who also provided a free download service that had the added advantage of slicing the files up into manageable chunks. The data though was less than accurate in the coastal region of Chile.       With Luis we traced the NavCenter files to their source and Luis wrote a very reliable Email robot to slice and dice the files and present them in a very compact form. I could now request the files over my Iridium phone and get a 4 day forecast that covered 1000 miles around me and could be downloaded in less than a minute. $1.50 for a good forecast – what a deal.       Now I started putting this all together and writing code. MaxSea was an excellent charting program but I found it took far too long to load when I just wanted to look at the weather plus the picture was far too cluttered. So I wrote my own viewer – or rather adapted my depth plotting program DeepPlot to display the data as simple wind arrows. A mouse click allowed you to scroll through the file in six hour time slices and animate the wind arrows.       When you download a conventional weather chart you typically get the Isobars and from there you try to compute the wind speed and possible direction of the systems. Although the expert forecasters are much happier with the upper air charts and can make very informed decisions on what the weather is going to do, most of us want to look at the data presented as simply as possible so a decision can be made in a few minutes as to what to do.       One drawback with these Grib Files is that they are generated in the bowels of a super computer and are usually unchecked by humans when the data comes out. The data forms part of what a meteorologist uses to make a weather forecast. The forecaster uses satellite imagery, station observations and a lifetime of experience to make the right decision. So using raw grib files can be extremely dangerous.       So how can we quickly validate the data and supplement it to make a proper decision? The answer lies in the SkyEye system. By overlaying the current model on the satellite image you can quickly and easily evaluate the data and see if the model reflects reality. Experience has shown that the model will tend to follow reality on a broad scale but the speed and direction of travel of systems can vary hence the need to keep a close eye on everything.       So this brings us to Puerto Toro on Isla Navarino about 50 miles North of Cape Horn and we are looking at the data and deciding if today is right for leaving for Antarctica. I have been looking at the models for 3 days now and am convinced that we have an excellent window of opportunity. There will be 12 hours of light headwinds 24 hours into the trip and the long term arrival 5 days in the future looks like strong Easterly airflow over the Antarctic peninsula.       On the other hand we have just taken a weather fax that shows 2 very nasty lows heading to Cape Horn. The Weather Fax shows strong North Westerly winds imminent in the next 12 hours. The Grib and satellite pictures also show the lows but they are forecast to weaken and provide a fair wind for moving South.       Greg and Keri, the co skippers take a chance. If they believe the Weather Fax we will lose 2 days at least . So we leave. The Drake has never been so peaceful and Cape Horn looks more like a tropical island in the sunset rather than the forbidding headland it is reputed to be.       As expected we get our headwinds and we have 12 uncomfortable hours after which our fair winds return and we make a fast trip South. We did learn on the way that 5 days is very ambitious for the Grib model and the data comes apart after about 3 days as our Arrival in fact had a Westerly component – forecast well enough ahead so 3 days in to the trip we had already made our landfall destination Deception Island. We could even give an ETA to a fellow yacht who needed parts to repair their rigging.       So the trip was a huge success. The technology worked and we had no surprises in the weather. The expedition proceeded, peaks were climbed aided by reliable weather, primarily Satellite image based as visibility was a prime concern. Boat movements were scheduled up to 2 days in advance to ensure the boat entered the treacherous rock strewn anchorages in calm weather and that the boat was securely tied to the shore for the 3 storms we encountered.       The last challenge was the return. Nearly every boat gets hammered as they approach the Horn. The week before one boat was knocked down, another lost a forestay and a third was forced to run off for 100 miles before a huge gale and had to beat back to the Beagle Channel.       We left in bright sunshine and motored 80 miles slightly West of our destination and clear of ice. The wind as expected came close hauled on a starboard tack and we made good Northing. Most of the trip we were expecting Southerlies with light Westerlies on the arrival. The Southerlies only lasted 24 hours and then we watched a low come in. Here we tested the system to the max. We expected the center of the low to pass 60 miles to the North. It in fact went just South of us and we got quite strong Westerlies. We had by that time a slot for arrival at the Horn 30 hours ahead riding a South Westerly ahead of a strong North Westerly – the best arrival if we got it right. So we hove to for 6 hours and when the wind veered round we made sail and put on speed right for our destination. We arrived bang on the money and had 25 – 30 knots on the beam the last 18 hours making right for our destination.       We were tied up and drinking pisco at the bar when the next warm front, wind and rain come through. Jonathan Selby Director - Software Development Xaxero Marine Software Engineering Ltd To learn more about the technologies mentioned in this article visit: www.xaxero.com www.globalmarinenet.net www.northanger.org www.iridium.com www.iridiumsea.com> ...return to BACKGROUND index page