We knew from the start of the project that we wanted to design and engineer the most advanced pedal-powered boat in the world. It’s crucial that the boat is strong, relatively easy to pedal, as light as possible, stable, and small enough for us to be able to propel but large enough for us to move about in easily. It has to carry everything that two people need to survive for up to 90 days, make electricity and water, protect us from the elements, be a home, a bathroom, a kitchen, a toilet, a bedroom and a hospital – and then there’s the small matter of two idiots being able to pedal it 3000 miles through some of the roughest waters in the world.
The design has come a long way since original concept drawings, but the layout is very similar. For a boat of this size (<10m), there’s always a wave on the Atlantic big enough to capsize it, regardless of how stable it is. Multihull boats are very stable, but once inverted they are almost impossible to right. For this reason, we knew out boat would be a monohull – less stable initially, and so capsizeable, but with the right design a monohull can be made to self-right: to roll itself right-way-up in the event of a capsize without intervention.
To protect us from the elements and reduce our aerodynamic drag, we also took the brave decision to design an enclosed boat. While this will result in a high cockpit temperature, it will hopefully allow us to continue to conditions that would result in an open boat having to stop or slow down. With careful ventilation, we believe we can bring the cockpit temperatures down to reasonable levels. We knew that our heaviest consumables should be in the middle of the boat to prevent the centre of gravity shifting as we consume our stores, and we knew we wanted the pedalling position to be near the centre too (to limit rotational pitching experienced by the pedaller).
From these initial ideas and decisions, we set out to design the most thoroughly researched and tested pedalo in the world.
The first section of the boat to analyse and optimise was the lower hull – the section of the boat that interacts with the water. Mark started by speaking with renowned ocean rowing boat and sailing yacht designer Phil Morrison, who talked Mark through some design principles. We then reached an agreement with the team at Newcastle University’s MAST towing tank, who allowed us free use of their 37m hydrodynamic test facility. We started with three test models – the current ocean rowing boat (as a baseline), a shape based on a yacht hull and a radical deep-V anti-slamming hull. John Burn Ltd provided tooling board to make the models, which were CNC machined by Concept Group International. These first three models showed us the design direction for the hull, after we ran them through the tank at a variety of speeds, yaw angles and wave conditions.
The second round of testing used another pair of models – this time, with the same hull profile, but a difference in beam (width). This was to establish the penalty we’d pay for making the boat wider (in so doing, making it easier to use and more comfortable). The results were promising, and showed us that the boat didn’t need to be extremely narrow to perform well.
After revisions to the hull shape that Mark had been slowly refining over several months, we performed a final test on a sixth hull model. This model included appendages such as the rudder and drive leg, and allowed us to determine the hydrodynamic drag of the finished design in all configurations. The results were very positive – the hull shape alone has up to 40% less hydrodynamic drag than the rowing boats. Much of this advantage is lost due to the drag caused by the drive leg, but we know that our boat can be relatively fast through the water and handles waves well.
With the hull shape and size established, we then set about working our how big the internal compartments of the boat needed to be in order to accommodate all of our kit and ourselves! Many different layouts were considered, with the most difficult decision being whether to have one or two pedalling positions. For reasons of access, complexity, space and usefulness, we’ve opted to have a single pedalling station.
To determine storage volumes and living space, Mark measured, weighed and modelled every single item that will be loaded on board. This extended to our own bodies – cue a white lycra gimp suit and a sophisticated scanning machine at Bentley Motors, which scanned us to create 3D CAD data of our shapes. Mark then articulated these CAD models, resulting in anatomically correct, full adjustable digital versions of us. Using all of this data, we’ve been able to wrap the shape the compartments and the whole boat around all of the kit we’re taking and adjust living spaces to sizes we know are usable. This digital work has been checked by then building mock-ups of sections of the boat, which we’ve crawled around in and evaluated. While the boat will be tiny inside, we know it’s big enough for two guys to live in!
With hydrodynamics and packaging sorted, the final task for the exterior surfaces of the boat was to analyse the aerodynamic performance of the shape. We won’t be going fast enough to create a lot of aero drag, but we needed to evaluate how the boat will behave in headwinds, tailwinds and sidewinds. It is important to us that we receive no more wind assistance than the rowing boats, that the boat does not become impossible to pedal forward in a headwind, and that the boat heels in the right direction when in sidewinds.
Our initial plans involved building large scale models of the boat and testing in a wind tunnel. While resource for this was secured, our timing plans couldn’t be worked around the availability of the tunnel. So, we instead decided to use Computational Fluid Dyanmics (CFD) to model the airflow over the boat in the variety of wind conditions. This modelling takes a lot of computing power and specialist software, and so we’re hugely grateful to analysis company Exa for performing the aerodynamic simulation runs for us. Luckily, the streamlined shape of the boat yielded great results without any modifications. We have very low drag in a headwind, only very slightly less wind assistance in a tailwind, and the boat performs and turns well in a spectrum of sidewinds.
The drivetrain design is clearly crucial to the success of our adventure. It must be light, efficient, easy to service, and simple. The first concept for the drivetrain featured a vertical driveshaft with a right-angle gearbox at each end, but we quickly realised that this layout would be heavy and difficult to fix if it failed without taking heavy spare gearboxes. It was Dr Ulrich Eichhron, Head of Engineering at Bentley Motors, who first suggested we investigated using a belt drive. On researching this, we instantly knew it was the right way forward. Modern belts don’t stretch, are very efficient, are light, don’t need perfect alignment (unlike chains) and crucuially can be twisted – meaning the direction of rotation of the drive train (from pedal to propeller) can be changed without a gearbox. We contacted Gates Corporation, the world’s biggest and most renowned drive belt company, who joined the project immediately and have since helped our colleague Paul Fish design the drive system.
The original boat concept had a propeller at the stern, but with the amount of vertical pitching that the boat will do in rough seas we noticed that a stern prop could be lifted out of the water. For this reason, and with the pedalling position in the centre of the boat, we decided a propeller on a keel board directly under the pedaller was the best solution. So, the drive system is a two-stage belt drive, taking power from the pedals and first gearing up from 80rpm pedal speed to 320rpm input speed to the inter-stage hub unit. This is a 14-speed internally geared Rohloff Speedhub 500/14, which is a sealed, anodised aluminium hub that uses epicyclic gears to deliver a gear range of over 500%.
This means that we have a reliable way of changing how much effort it takes to turn the propeller - handy if we have a tailwind and want to really run the boat quickly, or if we’re in a headwind or rough seas and want to give our knees an easier time. The power is sent vertically from the Rohloff unit down the keel drive leg to the propeller, mounted on a sealed propeller shaft. The propeller itself is being designed by specialists Bruntons, optimised for our low speed and power input and returning 82% efficiency. It will be a twin-blade, large diameter prop, to be manufactured in aluminium and then anodised.
The result of over a year of design work is a fast, stable boat that cuts well through the water and the air. At over eight metres long, it’s huge for a pedalo but tiny for a place for two people to live for over six weeks. However, we know that it can store everything we need, that we can live in it relatively comfortably, and hopefully we’ll be able to pedal it across the Atlantic!