Frequently asked hovercraft questions

How does a Hovercraft work ?


1.  The Skirt - The skirt traps air underneath the craft.  The skirt is made up of several individual pieces called segments.  Each skirt segment is attached to the craft's hull by batons on the outer edge and by plastic cable ties on the hull's underside.  They are attached in this way so that they create a tight seal to prevent air loss and so that they can mould and fit to the terrain the hovercraft is passing over.  Using segmented skirts also allows for individual replacement should it be necessary.  Skirts can take a lot of punishment.  Should a skirt become snagged on something, it is designed to break the plastic cable ties holding it in place rather than tearing the skirt segment.  If the wire ties break, the hovercraft's air cushion will still be maintained since the neighbouring segments will billow out to fill the new gap.  In an unusual situation where a hovercraft might lose many skirts, it will still be able to hover.  It is always recommended to keep your skirt in the best condition possible to experience optimum performance.

2.  Steering - Viper Hovercraft use a motorcycle type handle bar for steering.  Turn right, the craft turns right.  Turn left, the craft turns left.  The handle bar is connected by cabling to the rudders on the rear of the craft. The air that is used for thrust passes over the rudders to provide the directional control.

3.  Seat - The seating is arranged on the craft's centre line (inline).  This is to allow for proper hovercraft trim.  This prevents the craft from leaning to one side or the other while carrying its operator and passengers.

4.  Engine -  Viper Hovercraft use the same engines used in light aviation.  These are either two or four stroke, which are amazing light for there power output. To be used in aviation, these engines must be reliable or they wouldn't even be a consideration.  When properly maintained, these engines can run for hundreds of hours before needing a overhaul.

5.  Transmission - The power from the engine is transmitted to the fan by a belt and pulley system.  A small pulley is mounted to the engine's crank shaft.  A large pulley is connected to the fan shaft via a flexible coupling.  A timing belt is routed from the pulley on the crankshaft to the fan pulley, thereby turning the fan.

6.  Fan - The hovercraft's fan is made of plastic composite fan blades and a aluminium hub.  Viper Hovercraft uses an integrated design, which means that one fan provides both thrust and lift. 

7.  Fan Duct - The fan duct serves to increase the flow of air through the fan.  The fan duct also provides protection from the rotating fan.  In the unlikely event of the craft rolling over, the fan duct also acts similar to a roll bar.

8.  Rudders - Rudders are used to channel the thrust air either left, right or straight ahead.  The purpose of the rudders is to turn the hovercraft. Experienced hovercraft pilots use both the rudders and leaning to help the craft turn.

9. Elevators - Elevators are used to channel the thrust air either up, down or straight ahead. The elevators are controled at the cockpit by the operator. The purpose of the elevators is to manually control the trim of the Hovercraft.

10.  Splitter Plate - This plate splits the air that has passed through the fan.  The splitter plate is positioned behind the fan is set at one quarter of the duct's opening.  One quarter of the air is split under the hovercraft for lift, while the remaining three quarters are diverted out the back to give you thrust. The air that is used for lift passes under the splitter plate (the dividing point separating lift and thrust air) and through the craft's hollow inner hull.  The air exits the inner hull through holes throughout the craft's perimeter, each aligned with a skirt segment.  This escaping air billows the skirt segments and pressurizes the space between the ground and the craft's bottom hull.

Where can a hovercraft operate ?

Viper Hovercraft can operate on mixed terrain including water, sand, gravel, mud, salt flats, snow, ice, concrete and bitumen.  No jetties or landing pads are needed as the hovercraft can hover directly from the water up a sloping surface such as a beach, bank or ramp. Viper Hovercraft can operate in debris littered waterways where conventional vessels experience difficulty. On land Viper Hovercraft can operate over dykes and up banks providing there is a slope at the bottom. Viper Hovercraft can operate in wind conditions of up to 25 knots, 500mm waves and 1.5m swell at reduced speed


Where can a hovercraft not go ?

Hovercraft cannot operate over any surface which does not seal in the air cushion. This includes cattle grids, small trees, small bushes and scrub. Operation may be limited on certain types of stiff grasses and small plant due to air leakage through the foliage as the stiffness of the plant may be sufficient to hold the hovercraft skirt away from the ground surface.

Do not consider buying a hovercraft if you can use a more conventional vehicle/vessel.

How fast can a hovercraft go ?

This is dependent upon a number of factors including the size of the craft, engine, load, surface, environmental conditions and skill of the operator.  Sometimes increasing the engine power does not increase the maximum speed because the speed is limited by the stability of the skirt system. As the hovercraft moves forward through the air it encounters air resistance which exerts a pressure on the skirt at the front. When the pressure approaches the same as the cushion pressure, the skirt starts to loose structural stability and therefore becomes unstable. Typically a high speed design will operate at a higher cushion pressure and conversely a low pressure design will not be able to achieve high speeds. In all design situations there is a trade off between many factors. Designing for high speed alone would produce a hovercraft that was difficult to handle at low speeds and may never be able to get over hump speed due to large wave making resistance formed by a high cushion pressure.

What licence is required ?

Each country has its own licensing requirements and should be ascertained from the relevant marine or air operators' authority.  In Australia this is controlled by the Department of Transport, Marine Division.  For private operation an ordinary boat licence is required with a limit on craft size of up to 12 metres length.  For commercial operation a coxswain's ticket is required which is endorsed by the Department of Transport after training on the specific hovercraft is undertaken by a recognised training authority.

What training is required ?

Learning to operate a hovercraft has much the same level of difficulty as learning to drive a car. Viper Hovercraft provides training on all its hovercraft.

Hovercraft and the environment

For any vehicle to operate economically, the drag or resistance to motion, must be kept to a minimum.  On water, the majority of drag arises from the motion of the vessels hull through the water; therefore we can reduce drag and consequentially propulsive power by minimising hull contact.  The hovercraft achieves this by using low-pressure air to form an air cushion underneath it, thus actually lifting the hull clear of the water.  In addition, by using air propulsion to generate forward movement, the hovercraft becomes amphibious, and able to traverse land, soft terrain or water.

Being amphibious, the hovercraft can use direct routes across sandbanks, marshes and flats, with no loss of speed or comfort.  Environmentally disruptive channel dredging becomes unnecessary, whilst rivers and tidal estuaries present no problem for the passage of the vessel.  Previously inaccessible areas may be accessed economically with little or no impact on their environment.

Hovercraft do not damage the shore environment, such as beaches, mudflats and vegetation due to the hovercraft's low pressure "footprint".   For example, the average human being when standing on a beach exerts a pressure of some 3lbs per square inch underfoot, rising to 25lbs per square inch when walking.  The average hovercraft by comparison, exerts a pressure of approximately 1/3lb per square inch on the surface regardless of speed.  This "footprint" pressure is less than that of a seagull standing on one leg!

Hovercraft create virtually no under water noise, just atmospheric noise levels that would be typical of a diesel truck or bus.  The fact that there are no underwater protrusions or propellers eliminates the usual thrashing noise signature associated with conventional propeller driven craft, as well as negating any possible seabed erosion when operating in shallow waters.  It therefore becomes obvious that fish and other marine life are in no way affected.  This has been confirmed by independent scientific tests.  The major noise factor with any hovercraft is the propeller noise, which in any case is largely directional in characteristic. Viper Hovercraft propulsion systems have been designed to minimise atmospheric noise.

There is no exhaust discharge into the water as with most conventional watercraft, thus eliminating the pollution of the marine environment by oil and fuel particles, particularly prevalent with outboard motor usage.  The low friction with the surface, and subsequently low power requirements, the hovercraft is in itself a fuel-efficient mode of transport, thus lessening the pollution of the atmosphere even more.

The wake created by the passage of a hovercraft is minimal, ensuring that riverbank erosion and damage to foreshore by the waves created is virtually nil.  A study in the United Kingdom concluded that the passage of hovercraft over inter-tidal areas caused no damage to sea grasses or invertebrates.  It was also noted that bird life rapidly adjusted to the presence of hovercraft.  This has been confirmed on the Gold Coast in Australia, where a commercial operator passed over the same area of beach many times a day for more than four years without any affect to the 'Yabbie' population actually living in the sands directly under the flight path.

Are Viper Hovercraft expensive ?

Some may ask, if it is so simple, why is it expensive ? Well, for starters, not many hovercraft are made. Most, if not all Hovercraft are hand made, so production costs are higher than mass producers. In addition to this, the components required to build a good design, such as light weight engines and high end fibreglass composites, come at a considerable cost to the manufacturer. As far as Viper Hovercraft prices go, we try to build at a price equal to a boat the same size and power, using the best engines and materials available. Realistically, the retail price should be 30% higher than advertised, when compared to some other hovercraft makes available.


VIPER HOVERCRAFT
A Division of NELL FABRICATION
Goulburn. N.S.W. 2580 Australia
Ph: +61 418649350
sales@viperhovercraft.com.au

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