When you leave dry land behind and head out to sea, you're subject to the mysterious rhythms of this strange, fluid world we live in.
The oceans are never still; huge currents sweep across them. Like people-movers at the airport, if you go with these currents, you speed along; go against them, especially at low speeds or under sail, and you may end up going nowhere fast. Even a high-speed motor yacht can be borne off course by the power of the water beneath it.
Most people are familiar with the current in a river – it is a simple effect of gravity, as the water in the river falls down a gradient towards the sea. But oceanic currents are far more complex. These flows of hot or cold water are driven at the most basic level by the earth’s rotation. As the solid globe spins, the liquid oceans slide across its surface.
The complications arise when the winds and coastlines get involved – not to mention the depth, salinity and temperature of the water itself. Hot water tends to spread from the equator toward the higher latitudes. Cold water flows from the poles toward the tropics. Hotter water is less salty, hence less dense, and rises, while colder water is saltier, denser and tends to sink.
In 1513, Ponce de Leon wrote of the fierce current that drove his ships from the Caribbean toward Florida. This marks the first written mention of one of the world’s most famous ocean currents – the Gulf Stream. The Gulf of Mexico is heated by the sun; the hot water rises and streams out through the Straits of Florida.
If you’re heading to The Bahamas from Florida, you have to cross this 50-mile-wide “stream” in the Atlantic to get there. As you enter the Gulf Stream, the sea temperature rises and you’ll be swept north at two to three knots. But if there's a wind blowing from the north, the friction between the north-flowing current and south-blowing wind will heap the sea up into uncomfortably large (15- to 20-foot) waves.
The best time to cross the Gulf Stream is in summer when the winds are calmer, but as most owners want to head to The Bahamas in winter, you need to pick your weather window carefully....
As the Gulf Stream reaches Cape Hatteras, it shoots offshore, taking its hot water across the North Atlantic. During the spring, many yachts hitch a ride east towards Europe. Off the British Isles, the current, now called the North Atlantic Drift, splits. One branch heads north towards Scandinavia, keeping the Nordic ports free of ice.
The British Isles lie on the same cold latitudes as Canada, but the current makes them around 5°C warmer – hence you rarely see a white Christmas in London, England, but you usually will have one in London, Ontario.
The southern branch of the stream becomes the Canary Current and heads back across the Atlantic towards the Caribbean. As it moves, it pulls colder, saltier, denser water down from the polar regions to be warmed near the equator. It also picks up low pressures off West Africa that can turn into hurricanes. This current carried Columbus across to the Americas, and to this day it’s the most common route for boats heading to the Caribbean for the winter.
This famous current is just one of dozens around the globe. Giant oceanic rotations, called gyres, move clockwise in the Northern Hemisphere and anti-clockwise south of the equator.
Used wisely, oceanic currents can help transport your yacht with greater efficiency. Try to fight them, and you may find yourself wasting a lot of fuel.
Are you current on oceanic currents? Which one gives yachts the fastest ride?