Hovercraft Design – There have been a number of very futuristic hovercraft designs touted via the Internet of late that somehow lack credibility, so here are some of the features we think hovercraft designers need to consider before sourcing investment.
How to design a good hovercraft
Hovercraft need a low centre of gravity, otherwise cornering is a nightmare. If the design is top heavy, it simply isn’t going to corner very well – and cornering is important, you need to change direction now and then, to miss trees, people and boats.
Hovercraft need good clean airflow through the duct, another reason why hovercraft designs tend to be low, open and streamlined.
Hovercraft need to be very light, so designers should consider weight versus durability – make them too light, and they lack durability and don’t last so long.
Segmented hovercraft skirts are better than one piece skirts, since you can change sections when they get worn. We fit polyurethane coated anti-rip nylon weave, we tried neoprene coated nylon but found that material prone to UV sunlight degradation (not that we get so much sunlight where I live). Hypalon tears too easily.
Hovercraft engines. We prefer single engine designs to separate thrust and lift engines, to reduce weight, reduce fuel, reduce maintenance and simplify controls. Twin engine design lift engines tend to be sited at the front of the hovercraft so are subject to hitting a wave and sudden lack of lift – not so good to loose lift before thrust, you tend to fly over the handlebars! Hence one engine designs are best.
Engineering – keep it simple – a good design doesn’t need engineering complexity, so do away with elevators, trim levers, reverse buckets etc. Hovercraft can spin on the spot, so reverse isn’t a very useful feature. A simple design makes operation easy for all.
Hovercraft can plough into the water, so trim is important – we fit anti-plough skirts and have designed an anti-plough air management system.
Some people ask – why not make electric battery powered hovercraft ?- batteries are heavy, hovercraft are weight dependent.
Toy hovercraft with dual ducts and independent engines look swish, but small ducts are not very efficient, we prefer to make the duct as large as possible for greater efficient throughput of air. If the duct is smaller, (as in the twin duct design) you need more power to get the air throughput, so may have to rev the engine faster. Most of the noise generated from hovercraft is generated from the wind rush generated at the tips of the fan blades, so slower rotating blades are far quieter than fast rotating fan blades – fast revving engines are noisier than slow revving engines. More powerful engines can push more air through the duct by having a higher fan blade angle, so a more powerful engine can sound quieter than a less powerful engine.
Whatever the arguments for and against 2 stroke or 4 stroke engines, although 4-stroke engines are quieter than 2 stroke engines, most hovercraft noise is generated by the tips of the fan blades, so a quieter design results from careful duct design – large, with uninterrupted airflow.
Hovercraft payload. Starting on water – hump. All hovercraft create a pressure wave when starting on-water – it takes more effort to get over the hump or pressure wave. Generally hovercraft can lift 50% more weight when starting on land, so drill down to on-water starting payload when choosing plans to make a hover craft. Some suppliers only mention on-land payload, it makes their hovercraft look more capable, ask for on-water payload. If your hovercraft cannot lift the weight of you and your passengers when starting on water, it could be a long swim home!
Safety is important, front and rear guards are essential to keep little kiddies away from those horrible swishing fan blades that rotate at 2000 rpm. Self-build hovercraft enthusiasts making their own designs have lost the occasional finger from unguarded fans, professional hovercraft are guarded front and rear. Some designers offering cheap hovercraft leave off fan guards to improve air throughput, as this allows them to design the hovercraft with cheaper less powerful engines.
Hovercraft hull material. Glass fibre can shatter on impact leaving you with an expensive repair bill or trashed hovercraft – we manufacture hulls from highly durable buoyant HDPE and Carbon Fibre Composites. Ofcourse some will say – “they make boats out of GRP” – yes they do, but hovercraft glass fibre tends to be ultra light and ultra thin since hovercraft are weight sensitive – and not many boats travel up concrete slipways, over land and meet the occasional tree in their path!
Some designers use uprated engines – modifying an engine will invalidate the engine manufacturer’s warranty – no engine manufacturer wants his engine to run on high stress all day. If you are looking for a less stressful day, and expect full warranty, buy a Hov Pod Hovercraft!