Hydrofoils the key to success at AC35
America’s Cup Endeavour is not just about sailing. The core of the programme is the Steam curriculum — science, technology, engineering, arts and maths.
This week, readers can learn exactly what Bermuda’s middle schoolchildren are learning. Let’s start with T for Technology — straight from the Steam curriculum.
Technology is a key learning component for any student. It instils creativity and the ability to think openly, with the intent to inspire the next generation to drive future technology.
One of the evolutions that is discussed with AC Endeavour students is the technology that enables these incredible boats to fly. Hydrofoils are the buzz word of the America’s Cup and it is said that whomever can design the most efficient hydrofoil will likely win the 35th America’s Cup.
That being said students are given exclusive access by Oracle Team USA to spend one day of the weekly M1 programme at the base. They get an exclusive tour of the America’s Cup Class catamarans and research the technology behind the flying boats. One of the key things they learn is how hydrofoils reduce drag and enable the catamarans to generate enormous amounts of apparent wind. So basically, the less drag the faster the boats go and the more apparent wind they develop as a result.
Apparent wind is a fancy name for fake air or wind — something you experience on a scooter or by placing your hand out of a car window at speed. In simple terms, if there is no natural wind and you are doing 35kph (Bermuda’s speed limit), place your hand out of your car window you will feel 35kph of fake wind, known as apparent wind.
Why is this important? Well the more apparent wind you develop, the faster you go. So the reason hydrofoils are really key is they reduce hydrodynamic drag and create more apparent wind which makes the boat go a lot faster. Some of the America’s Cup catamarans have been able to do three times the true wind speed thanks to the incredible designs behind the hydrofoils. Don’t forget that they are lifting the whole boat, the wing and the entire crew — relying on a foil not much bigger than a surfboard lifting nearly six tonnes at maximum pressure!
The foils are made of carbon fibre, a modern material that is extremely rigid and has a very high strength-to-weight ratio. Students test the strength of a single fibre and gauge an understanding of the strength of these incredibly unique structures. They are built to the edge of their limits, of what can be structurally achieved.
A hydrofoil will sink if dropped overboard so people often ask how does it lift the boat clear of the water. The answer — The Bernoulli Principle. For any foil generating lift, there must be a pressure imbalance, ie lower average pressure on the top than on the bottom. Bernoulli’s principle states that this pressure difference must be accompanied by a speed difference. From Bernoulli’s principle, the pressure on the upper surface where the flow is moving faster, is lower than the pressure on the lower surface where it is moving slower. This pressure difference creates upward lift.
Your challenge is to hold a rectangular piece of paper close to your mouth, blow across the top of it and get the paper to move up. Sounds simple enough but give it a go.
What’s happening? You might find the results of this challenge surprising. You blew across the paper and it went up? You would think it would move down. Your fast moving breath has less push (less air pressure) than the still air below the paper. Hence why the paper will lift up. This is exactly what happens to the hydrofoils underwater.
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