As new technologies are introduced, I am always impressed how quickly the general public learns core scientific principles and then casually references them in general conversation. Case in point: the air resistance of a vehicle as it relates to speed. As far back as 1590, Galileo was dropping balls off the side of the Leaning Tower of Pisa to demonstrate how air resistance had a relation to the surface area and shape of an object and, more importantly, to speed. That makes sense – the faster an object is travelling the more air resistance it will encounter. It is not quite that simple though. When you look at the formula to calculate air resistance, the velocity component is squared. That means that when you double the velocity of an object, the air resistance will quadruple.

Consumers often lodged mild complaints that their new car never seemed to achieve the fuel economy quoted by the manufacturer. Australian Design Rule (ADR) 81/02 Fuel Consumption Labelling for Light Vehicles outlines a specific test procedure to arrive at the quoted figure – but this has the majority of the test below 40km/h. Only 4.5 per cent of the test is at 100km/h or above. You can achieve the quoted figure if you are prepared to drive at a slow enough speed. The figure is really more designed as a comparison among different vehicles with all the cars being tested under the same conditions. Consumers don’t really expect to achieve the quoted figure.

The issue is slightly different with electric vehicles though. They are typically quoted in range from one battery charge. Under the same test conditions, you can achieve the quoted range but the test conditions are not at highway speeds. Just by going from a speed of 100km/h to 110km/h, a seemingly minor increase, this will increase air resistance by 21 per cent. Another 10km/h increase in speed and your air resistance has increased by 44 per cent. The issue is more critical in electric vehicles (EVs) as people are looking at the quoted range to see the practicality of using a car in a certain set of circumstances.

Electric cars are making inroads (couldn’t help myself with that one) but electric boats are not quite as advanced. The bigger issue with a boat is they have to battle more than just air resistance. The surface area of the boat in contact with the water creates significantly more drag than air resistance. The total resistance to motion is still dependent upon a coefficient of friction and speed squared but, up to this point, electric boats have just struggled to have any decent range.

But now…a company is about to disrupt the luxury speed boat industry. Noting the issues with hull drag and battery range, the Swedish company, Candela, has decided to remove the hull from the equation. Much like America’s Cup yachts pop up out of the water on foils, the new Candela C8 is an 8.5m luxury speed boat that rides on hydrofoils. It can cruise through the water at almost 60km/h and with a relatively small battery pack of 44kWh it has a range close to 100km. The secret here is that the surface area of the hydrofoil in contact with the water is minimal compared to the full hull therefore reducing the drag over a normal boat. The added advantage is that the ride up on a hydrofoil is incredibly smooth compared to a full hull bouncing through the waves.

Tell me if you remember the days before 1991 when the Sydney hydrofoil used to transport people across the Harbour at

Mathew Dickerson

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