Two masts spanning 55 metres, swinging freely above your head, which at the top are just a bit wider than a school ruler… perhaps it’s hardly surprising that some people ask, ‘Are you sure Arc’s safe?’
It’s a reasonable question – whether you are in the cabin or walking beneath. How can we know if a design is truly safe before it has been built?
The HSE factor
When planning a large, complex engineering project, there are strict safety guidelines and clear regulatory frameworks in place which designers use.
Even though Arc has not yet been built, there is a method developed by the UK’s Health and Safety Executive to cover it.
‘We have some unusual challenges,’ says Simon Walley, Arc’s Head of Engineering, ‘but the structure, machinery and user experience we are creating all have parallels in other industries. The HSE method requires us to assemble and satisfy an Arc specific set of passenger safety industry standards.’
Weathering a perfect storm
With over 20 years’ experience in the marine industry, including work on the world’s tallest yacht masts, Simon knows that marine safety is more than adequate for Arc’s structure. The construction of Arc’s twin carbon-fibre masts is identical to the large masts used on superyachts – which need to withstand substantial forces at sea way beyond those in which Arc will operate.
Simon also drew on the design experience of 70-metre wind turbine blades which are now commonplace in offshore wind farms. Standing taller than Arc, the safety of these huge, load-bearing, composite structures is well understood - they are designed to rigorous codes, robustly proven by load tests and monitored throughout their lives by embedded fibre-optic strain gauges. Turbines endure a harsh, salt-water, gale-force environment, and (to disprove the old maxim) are struck by lightning on a regular basis!
Referencing such technologies gives the confidence that Arc’s twin cantilevered arms will be operated safely throughout their design life.
The machinery for Arc is important to its operational safety and, switching seamlessly between purposefully doubled-up systems, the ride will go on if, for example, a motor fails. Despite its superficial resemblance to a huge trebuchet, Arc is always kept in perfect balance – a whopping 100-tonne fan-shaped counterweight at the end of the arms balances the moment of the passengers, cabin and masts, so that, unless powered, the whole assembly won’t move. This ensures a low-energy, smooth ride. Arc uses the same ‘fail-safe’ and ‘mechanical redundancy’ philosophies that have been developed and refined for the aircraft industry over many decades. There’s no chance of a sudden drop.
Checking for safety won’t only rest with the design team. Arc, like every passenger carrier, must pass rigorous safety third-party assessments on every aspect of safety before it will be approved to carry passengers – and that means all the tests you can think of plus many more! It must also be continually re-tested.
Avoiding ‘high anxiety’
How about user experience? Well, Arc’s motion is smooth – much smoother than a cable car or standing on a moving bus. Our eyes notice speed but we only feel changes in speed, ie acceleration. Arc’s sophisticated motion control will assist the pilot to linger to enjoy the view or go a bit quicker to get you there.
The HSE guide even regulates “white knuckle” rides in fairgrounds (which are intended to scare the hell out of you). Arc will be a completely different experience, calm and serene.
So your Gran could walk the whippet beneath Arc – she will be that safe, certainly.
Whether she’ll go up with you remains to be seen…
The Germanisher Lloyd and DNV classification societies have rules for the Design and Construction of Large Modern Yacht Rigs and for Wind Turbine Rotor Blades, whilst fairgrounds and amusement parks are controlled by the 2007 Guidance on Safe Practice. It’s gripping stuff.
▲ Yacht masts on the move