Griffon Hoverwork talks hovercraft

Jon Lawson
How can hovercraft adapt to new roles, embrace new technology and stay relevant?

Griffon Hoverwork is currently the largest hovercraft manufacturer in the world, with clients in various industries from disaster rescue to defence. Mark Downer, engineering director, answers our questions about design, materials and propulsion.

What did COVID-19 do to your hovercraft business?

Covid-19 has presented challenges which we have learned to overcome. Always following the Government’s advice we have constantly reviewed our Risk Assessment and safe working practices to maintain essential capacity on the production line and the support team. Social distancing has had some impact on our capacity but the greatest risk is any delays causing our supply chain to be late in delivering components, delays to clients being able to participate in acceptance trials or delays to customer training.

We have been trialling high definition video conferencing for progress reporting, examination and trials to mitigate delays. We have also worked to design and implement craft modifications for Covid-19-related medical roles such as high-speed patient transfer between the Isle of Wight and the south coast hospitals in Portsmouth and Southampton. To date the work from all our whole team has been exemplary, minimising the effect of Covid-19 and putting us in a better position than others who have not been as fortunate.

What are you working on now?

Our top priority has been to ensure our users such as Hovertravel, coastguards, border guards and the RNLI are in a position to continue their essential work. We have just delivered a hovering cricket pitch cover and we are currently building four brand new hovercraft for fisheries and conservation, marine police and border guard roles.

What are hovercraft customers asking for?

Generally, customers have been looking for craft with increased capability, capacity and safety whilst being more environmentally friendly, especially with tighter emission controls. These requirements have driven the design process for our 995ED and 12000TD, allowing us to double the payload of a small hovercraft to 995Kg whilst maintaining road trailerability and introducing state-of-the-art dual diesel-electric technology.

Is the role of hovercraft changing?

We are seeing a growing demand for vehicles that can overcome and respond to challenging, transitional environments in light of the effects of climate change. Extreme climactic events such as flooding affects tens of millions each year whilst global warming continues to raise new challenges across our planet.

Governments, navies, NGOs and coastguards are looking to plan disaster relief operations that don’t rely on conventional vehicles built for conventional environments; hovercraft can form a vital part of that operation.

Hovercraft offer a platform to users for moving a high payload at high speeds across cluttered environments and areas that cannot be accessed by other forms of transport. This trend in the ever-changing global environment continues to increase with essential government operations in areas where hovercraft excel.

Can you make hovercraft cheaper?

We are always looking for ways to make our craft more affordable for our customers and it is a constant factor in decision making and design. Our aim is to provide customers with specialised hovercraft that will provide the most effective, safe and long-lasting platform for successful amphibious operation. To do this, we source and develop the very best in marine technology to create high payload, built-to-class craft, proven in every environmental condition; from commercial to military. Whilst regulatory and statutory requirements tend to drive up costs, efficiencies in design are yielding better cost-effectiveness and value for money.

How has hovercraft design changed?

Hovercraft have evolved from designs based on aircraft in the 1960-80s to designs taking more account of the marine environment and regulations that were more like small fast boats from then until around 2015. Since then our latest designs have returned to using more aeronautical engineering combined with the latest automotive engineering developments all of which we specialise in adapting for the marine environment and legislative structure.

We look to develop structures as lightweight as possible whilst maintaining structural integrity to provide the highest possible payload for users. One significant latest change has been the introduction of aluminium adhesive bonding. In the 995ED the hull is completely adhesively bonded; allowing us to save 30% in overall craft weight with less than 1mm distortion to the hull form.

Is the hovercraft design process changing?

Design software such as Solidworks allows us to fully 3D model a craft, or sections of a craft. This brings several advantages, one being different systems can be brought together within one modelling space to check for any clashes or interference enabling any issues to be ironed out within the design team and are not passed onto production.

Computational Fluid Dynamics is also a tool used widely within the design department. The tool is used to both develop and improve our products as well as helping out customers with specific requests they may have on their craft. CFD allows us to visualise and determine how a change to a craft will effect it aerodynamically and more importantly what impact that change has to the flow of air entering the duct or lift system.

We have considered 3D printing for some specialist components but at this time we are not yet assured about material strength capabilities available for use in production hovercraft. We do not typically design with any bespoke small plastic components and therefore widespread 3D printing is not currently seen as an advantage to us in production. Whilst access to the best software is beneficial to the company, a large majority of potential lead time reductions occurs in the interaction between the design department, production and suppliers. We are seeing improved accuracy, less rework and greater schedule adherence to assure on-time delivery to clients.

Can You improve the user experience?

Our priority is in the safety and usability of our craft for the role they are used in. User experiences forms an integral part of this. For example, in the 12000TD passenger hovercraft user experience was key. For this spacious, comfortable passenger seating was installed in an air-conditioned cabin with internal noise below 75dB. Access was moved from the sides to the bow of the craft using stairs and a ramp for fast entry and exit. Our ducted propellers allow for slower tip speeds, reducing the external noise significantly.

Are there advances in power electronics for hovercraft?

EmpirBus DCMs are used on most craft to simplify power distribution as well as using them to control various alarm functions on the craft. The distribution network means considerably less cable is required, saving overall weight in the craft. Most larger craft built will have extensive power networks requiring a mixture of AC and DC power. Recent advances in MasterVolt technology has made transforming power more compact, whether it is supplied from the batteries, engine or shore supply, taking up less space in the service bay as well as weighing less.

Our standard navigation equipment fitted to the craft is continuously updated incorporating the most up to date features and navigational aids.

Will hovercraft ever be autonomous?

Autonomous hovercraft is a very real prospect in the near future and we are preparing for this to become reality. Particularly in logistics supply across amphibious environments.

Talk me through your recent hovercraft patents

Our most recent patent was for the mixed flow fan design we use in the lift system on our newest craft; 995ED and 12000TD. We are constantly innovating, incorporating new applications and using the patent process to protect our Intellectual Property.

Is there still much physical testing in hovercraft production?

All of our craft are put through a rigorous testing procedure to ensure each performs as intended and there are no shortfalls. This remains a requirement for Flag authorities and IACS and annual surveys.

At component level, we recently developed a new skirt fabric for craft that are used in harsh ice environments. Part of the development included 6 months of overall testing of the material fitted to hovercraft in a wide range of conditions and environments. Testing was imperative in determining the suitability of the fabric for a hovercraft skirt.

Have there been many material changes?

Apart from the above, the standard hovercraft skirt fabric hasn’t changed much over the last 20 years. Thrust propellers were unguarded and over the years have transitioned to ducted propellers with a variable pitch, larger diameter, reduced noise, while efficient and high power-weight diesel propulsion has replaced gas turbines, with increased use of composites.

What more material advances do you foresee for future hovercraft?

Marine aluminium still currently provides the greatest build material for long lasting, robust hovercraft hull design to survive challenging environments. As adhesive bonding allows us to offer increased payload we continue to develop this for larger structures. Aluminium will remain the most effective build material. We are starting to introduce composites into the craft but these do not form part of the structural integrity. On the 995ED most of the topside structure that you see is GRP and has been CRP for some projects. The GHL-patented mixed flow fan is now manufactured from carbon fibre.

How can hovercraft props be made better?

The propellers on a hovercraft have always been the main source of noise. The noise produced by the props correlate to the tip speed of the blades. Reducing the tip speed would lower the noise level but as a result of this, the thrust generated would be sacrificed. A prop design that does not sacrifice thrust but also produces less noise would be extremely beneficial on a hovercraft. Any reduction in weight would also be advantageous as weight is the single most important variable in hovercraft design and operations.

Are lubes improving in marine environments?

Yes, recently we have worked with one of our propeller suppliers to change the grease and lubricants that are used on the hub of the propeller. The new improved grease should equate to a longer lasting product in the marine environment.

What’s the latest in marine diesel?

Tier 4/IMO III marine engines are the latest diesel engines in the marine industry producing the least amount of toxins into the atmosphere. Tier 4 engines are fitted with Selective Catalyst Reduction (SCR) amongst other technology to reach the latest guidelines set out by the IMO.

What options are there for alternative hovercraft?

Griffon already manufacture a diesel-electric hovercraft, the 995ED. Unique to this model are its two standard power modules each containing a diesel engine driving an integral lift fan and electric generator.

Alternative fuel options such as biofuel, compressed air, alcohols and others are constantly monitored by the design team but this technology is currently impractical for hovercraft use. The weight, power and cost penalties are too great compared to traditional fuels but this sector will most definitely evolve in the years to come. Looking to the future, new technology to allow for fully electric hovercraft is approaching; we are working to ensure we are ready to utilise this.

Where are we with marine batteries in hovercraft?

Batteries are entirely feasible in terms of technology readiness, but less so when it comes to hovercraft operations. The current energy per unit weight (kWh per kg) in modern batteries only allow for extremely time-limited hovercraft expeditions, therefore conventional diesel engines remain superior for power to weight ratios. Although this sector is rapidly evolving and a fully electric hovercraft could very much be viable in the coming 3-10 years.

What about fuel cells?

Whilst hydrogen fuel cells have plenty of advantages such as very low vehicle emissions other than water vapour and a high fuel economy, this technology is still incredibly expensive.

It also requires extremely high pressure, on-board hydrogen storage which is difficult in a vehicle such as a hovercraft that is constrained by volume and weight. Hydrogen is expensive to transport and there is no infrastructure in place to refuel a hydrogen vehicle. This is also another technology that we expect to rapidly evolve and become viable in the near future.

Unlike other maritime transport, hovercraft do not require the same level of infrastructure to operate. Rather than relying on dredged channels, docks or pontoons, they can fly over the undisturbed marine environment to land on unprepared beaches or slipways.

Whilst still reliant on diesel engines for lift, when accounting for the wider picture hovercraft allow for environmentally-sensitive operations. We continue to incorporate the latest technology and innovations to ensure our hovercraft range is as green as possible and compliant with environmental regulation.