To end up where you want to go, its common practice to point in the direction you want to go, and go via the shortest route! Seems logical enough, as you don’t normally walk around the block if you if you want to head to the kitchen to make a sandwich!
© Conrad Colman / Great Circle
Anyone who is familiar with Google Maps is comfortable with the idea that driving a longer route on a motorway is potentially faster than a shorter route on bumpy country lanes. However, this scenario of more miles at a faster speed only holds up if you can indeed go faster, otherwise, a longer route at the same speed is always going to be a losing proposition. This is where naval architecture comes in.
© Ainhoa Sanchez/Volvo Ocean Race
Looking back through the history books, I stumbled on the above map of the original race route in 1973. The first-ever leg in the race that would later become the Volvo Ocean Race was won by a yacht called Burton Cutter, who sailed the direct route to Cape Town over the top of the South Atlantic high pressure. While it won the leg, the upwind conditions may have contributed to the boat’s short life in the race as it almost sank in the next leg. Tough upwind conditions across the top of the South Atlantic anticyclone again contributed to boat damage in 1985 when more than a couple of the 80-foot maxi class suffered major delamination just off the African coast.
© Photo Rick Tomlinson
The Maxi racing yachts from the eighties weighed 40 tonnes and were 80 feet long, and because of the rounded shape of their hulls and immense weight, went pretty much the same speed upwind and down, and more wind speed didn’t translate into much more boat speed. The 1985 24hr speed record was 317nm whereas the overall race record is held by Ericsson 4’s 2008 blast in the South Atlantic which netted 596 nm, almost double! 10 feet shorter but crucially, 26 tonnes lighter, Ericsson 4 and the Volvo Ocean 65s that followed are flatter, allowing the boats to surf on top of the waves instead of ploughing through them.
Now that racing yachts surf, accelerating sharply when not sailing upwind, navigation becomes more complicated because it is often worthwhile to sail longer distances, away from the direct route, in order to find more favourable wind angles. Ken Read, two-time Volvo Ocean Race skipper puts it succinctly. The optimal route “zigzags you all over the ocean, chasing weather, chasing storms, chasing whatever is out there that you can use to your advantage.”
The above butterfly-shaped chart is the key to this zigzagging and is called a polar chart. Polars record how fast the boat will sail at each angle of the wind in each wind strength. Notice how the lines are closely grouped at the top: this shows that sailing close angles upwind, the Volvo Ocean 65 maxes out at 11 knots. However, the droopy bottom shape shows that as the boat sails on a reach or downwind, it just keeps going faster and faster as the wind increases. If you follow the light green line that corresponds with 26 knots of wind, you go upwind at 11 knots, reach at 21 knots of boat speed and run downwind at 25!
Being able to sail 2.5 times faster downwind than upwind, certainly makes it worthwhile to sail the extra miles on the downwind motorway to Cape Town, safe in the knowledge that you’ll get there faster than if you had bumped your way upwind on the short route.
