WHEN WERE HOVERCRAFT DEVELOPED?
The very first air cushion design was proposed in 1716, but sufficient power sources only became available in the 20th century with the invention of the internal combustion engine. Initial hovercraft research and development was carried out in the 1950’s and 60’s in UK, USA, Russia and China. Sir Christopher Cockerell, the principal developer of the hovercraft in the UK, devised the Peripheral Jet System which made hovercraft a feasible means of transport.
Since that time the technology of skirt systems, ducted propulsion, aluminium and FRP structures, and high efficiancy power systems has been the focus. Since around 2015 focus has now begun on electrical powering of smaller craft, and hybrid power systems. Some SES projects are today looking at zero emission power systems based on fuel cells and battery driven electrical motors.
Air Cushion systems for industial load movement were also developed in the 1970’s and are marketed by a number of companies in Europe and the USA.
WHAT IS THE DIFFERENCE BETWEEN AN ACV AND AN SES?
An Air Cushion Vehicle or ACV, generally referred to as a ‘Hovercraft’ is a fully skirted amphibious craft. It is propelled by ducted propellers or fans.
A surface Effect Ship or SES (also called an Air Cushion Catamaran or ACC) is a slim hulled catamaran vessel that has its cushion between the hulls and skirts or seals at the bow and stern to contain it. In the 1970’s two contractors in the USA, Bell Aerospace and Aerojet General developed SES that could reach 100 knots on calm seas. Nowadays SES are used as ferries (in the Mediterranean for example), as military craft (the Royal Norwegian Navy have Minehunters and Fast Strike SES craft), and for Offshore Wind Farm service. They are economical craft and have a smooth ride in a seaway.
WHAT HOVERCRAFT OPERATIONS ARE THERE IN THE WORLD?
The ability for the hovercraft to operate in areas otherwise difficult to reach often means that they are out of sight to the general public.
Applications are diverse – passenger and freight vessels, military operations, coastguard & rescue uses, surveying and ice breaking are some examples. Military hovercraft have been in action in several conflicts, including the Vietnam War, the Falklands War and the Gulf War in Iraq. One characteristic of hovercraft is that they are almost completely resistant to underwater explosions.
The cross-channel hovercraft ferries between Britain and France ceased service in 2000. These hovercraft, designated SR.N4, were still the fastest commercial passenger-carrying vessels. Designed for 8-10 years service, they lasted for 33 and were so successful that there was no immediate need to build a new generation.
There area approximately 2,500 hovercraft in use today around the world. In 2021 the largest construction project for hovercraft is the replacement of the US Navy LCAC fleet with an updated craft called the Ship to Shore Connector (SSC)
Surface Effect Ships are also gaining market in 2021 mainly for Wind Farm Service duties.
WHAT ARE THE ADVANTAGES OF HOVERCRAFT?
With their amphibious capabilities and low cushion pressures, hovercraft have significant advantages over other modes of transport. They are less responsive than other watercraft, but much faster. Despite high speeds there is minimal wash, as they move over water and not in it. Difficult areas of terrain such as mud, sand, grass, ice, snow and very shallow water pose few, if any, difficulties for hovercraft.
Canadian Coastguard have used a hovercraft as specialized icebreakers since 1975 for the St Lawrence Seaway, including ice over 1m thick being broken using a combination of air cushion pressure and destabilization of the edge of an ice sheet. Ice breaks as hovercraft applies force from above an opens an air gap under the sheet, whereas ice breaking ships apply force end-on. One craft with a gross weight of 45t travelling at 15 knots is said to have broken ice up to 40cm thick in a path three times the craft’s width.
HOW DO HOVERCRAFT STOP?
There are no conventional brakes on a hovercraft. The cushion can be adjusted for skirt drag to help braking. The standard method of stopping quickly is to reverse the thrust until the speed is low enough to safely reduce the lift power, or to simultaneously reduce the lift power for a faster but less comfortable stop. The lift power can be cut completely for the fastest stop, but this can be very dangerous.
Smaller craft and racing hovercraft simply twist around their centre so they are travelling backwards and then apply full power for a quick on cushion stop.
CAN HOVERCRAFT REVERSE?
Hovercraft are generally not reversed, although some have limited reversing capability used for slow speed maneuvring. The majority of craft are able to make a complete turn in a short radius, if not around their central axis, so reversing is not considered to be an important function.
In an extreme emergency stop situation where other methods either fail or are unsuitable, a hovercraft might be spun around and full thrust applied against the direction of travel, although this is a dangerous manoeuvre for larger craft which can lead to capsizing and is unlikely to ever be necessary given safer methods of stopping suddenly.
WHY ARE HOVERCRAFT UNSUITABLE FOR ROADS?
Hovercraft use on roads is difficult, partly due to road camber and corner slopes. There is little room to manoeuvre, and dust and loose objects can be made airborne with both lift and thrust air creating a significant danger. The thrust air is too powerful for confined public spaces, and hovercraft have no conventional brakes. Noise also presents difficulties and prolonged travel over hard surfaces such as concrete and asphalt will lead to excessive skirt wear. In addition, road cambers demand great skill from the pilot to navigate with the bow pointing a little towards the crown of the camber.
IF THERE IS A TOTAL LOSS OF POWER, WILL A HOVERCRAFT SINK?
Foam or watertight compartments are included in the hull for buoyancy over water, just as for a boat. A hovercraft will therefore float if there is a total loss of air cushion pressure.
The hull of a hovercraft is also designed in a similar way to that of a boat so as to give suitable stability and freeboard when floating.
Passenger craft are designed to regulations set by marine authorities and so have to provide emergency escape routes, lifesaving equipment and life rafts for passengers and crew.
WHAT ORGANISATIONS REGULATE HOVERCRAFT?
This has long been an area of discussion.
Technically hovercraft fly as they float on a cushion of air, so some argument has been made that they should be governed by those organisations concerned with air transport. However, as they are in reality almost always in contact with the supporting surface due to surface irregularities, over water they are governed by maritime agencies.
Operations on land accessible to the general public carry significant safety issues, and are generally therefore limited to access points to areas of water unless the area is closed to the public.
Larger ACV and SES are generally built following the regulations of a ‘Classification Society’ such as Lloyds Register, Det Norske Veritas, Bureau Veritas, and the equivalent to these organisations in China, Korea, Australia etc. We have given links to these bodies in the ‘Resources’ page on this site.
WHERE CAN I BUY OR HIRE A HOVERCRAFT?
There are many organisations around the world that manufacture hovercraft and surface effect ships from one man racing craft to craft displacing hundreds of tonnes.
We have a listing of a selection of these under the resources section of this site – you will find a pdf document there to read or download.
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