Can't I just buy one?
You could, of course, buy a ready made craft rather than build one yourself!
In the UK there are only a few hovercraft manufacturers and the craft designs they offer are all very similar in style and construction - fine if you like the style but hard luck if you don't!
If you do an Internet search for UK hovercraft (or look at the Hoverclub UK web site) you will find most of the UK manufacturers. Alternatively you could buy a second hand hovercraft on eBay or some place else. If you have no experience of hovercraft then I would strongly recommend that you join the Hoverclub and find a member nearby who would be willing to show you a hovercraft in action. Buying is fine if you know a bit about what you are actually getting - it could be a nightmare if you don't! The Hovercraft Buyers Guide has information on some of the potential pitfalls when selecting a suitable cruising hovercraft.
What type of craft should I get?
The answer to this is a bit difficult! First you really have to decide where you want to use a hovercraft. If you want to race on inland courses then you need to buy or build a racing style craft. The Hovercraft Club GB has plenty of information available on the various formulas used in racing and the construction requirements for these craft.
The other alternative is cruising. Cruising in the UK is primarily carried out on or next to water (rivers, lakes, inshore waters, estuaries, mudflats, beaches, etc). The type of craft you can use will depend upon the type of water you wish to cruise on in the same way as choosing a boat. For inshore or sea cruising (or even larger lakes that can have big waves!) you need a craft that can handle these types of conditions safely. If all you want to do is cruise on small rivers or mudflats then a smaller, less seaworthy craft would be fine. You also need to consider the amount of weight the craft is designed to handle - do you want to carry passengers, camping gear, etc? If you look at the link page you will find links to information on craft types and their capabilities. If you still can't work out what you need then post a question on one of the hovercraft discussion boards (see link page) - there are plenty helpful people in the hovercraft community.
As I have no direct experience of building or operating racing hovercraft, this site only contains information on cruising hovercraft.
To cruise in the UK means having a seaworthy and stable craft. In my personal opinion, this automatically rules out small (under 11ft) hovercraft and many craft that have finger-only skirts. The actual performance of finger skirts is fine - the real problem is with their durability on rough water. They are designed to partially detach from the craft under heavy loads to prevent the skirt material tearing - this 'feature' makes it likely that multiple fingers could come loose on rough water. If this happens when offshore it could result in a loss of cushion and the inability to reach land. Not all finger skirt craft suffer from this potential problem - some more modern designs have more secure skirt attachments. A lot of craft designs also suffer badly from a condition known as "plough-in" - this condition results in the front of the craft hull coming into direct contact with the water surface at speed - which causes very fast deceleration. On small craft the driver can even be ejected over the craft nose during plough-in! Plough-in is caused by the front skirts becoming "attached" to the water surface and the resulting drag pulling the craft nose down until the hull itself becomes attached to the water. Good hull and skirt design can prevent (or at least minimise the effect) of plough-in.
The hull design is also critical to the stability and safety of the craft. It should have enough buoyancy to support at least 110% of the maximum craft weight including payload. The hull should also be designed to prevent flooding of the passenger or engine compartments during a stop on rough water. The hull really should provide similar protection and stability to an equivalent sized boat. The lift system should be capable of providing enough air volume to allow the craft to be used over choppy water or waves without losing significant cushion pressure. The mechanical components should be protected as much as possible from salt water or spray and the engine should be a low-stressed reliable 4 stroke type.
The other major consideration for a cruising craft is noise. In the UK, as in other countries, the issue of noise pollution is becoming much more important. Hovercraft have a reputation for being very noisy machines. Partly, this is due to the use of very noisy two stroke engines, poor exhaust design and noisy, inefficient fans used for thrust. In the interest of all current and future hovercraft owners, I would strongly recommend that you select a craft that is as quiet as possible - for a cruising craft I would not exceed a noise level of 82dB at 25 metres - roughly equivalent to a van driving past. It is currently easily possible to build practical hovercraft that produce noise levels less than 79dB - the same as a small car. Low noise levels also makes it much more comfortable for the driver and passengers!
Driver and passenger comfort are important considerations when choosing a craft if you want all year round cruising. A cruising craft should offer some weather protection to passengers - it's not much fun cruising along at 30mph in near zero temperatures and rain! Even a simple windscreen is better than nothing! Some larger craft can be fitted with heaters, windscreens, wipers and full covers to provide the best comfort level.
How do I go about building a craft?
If you do not have an in-depth knowledge of the design of the various elements of a hovercraft (very few people do!) and how they interact with each other I would strongly recommend that you do not try to design your own! Like most things, they are not quite as simple as they might look!
It's much safer and easier to build a proven design from a set of plans. The cost of a set of plans represents excellent value when you consider the amount of development time that has been spent on them. Basically you are paying for someone else's knowledge, experience and mistakes!
Once you have a working hovercraft then there is nothing to prevent you from attempting to improve it! Hovercraft are relatively under-developed compared to other modes of transport.
I have built from commercially available plans. I have built a Universal Hovercraft UH18SP, a Sevtec Scout and a Sevtec Prospector. All of these craft are US designed and are completely different, both in look and construction, to the typical UK cruising craft. A typical UK style hovercraft has a GRP hull with segmented skirts and a ducted fan producing both lift and thrust and is fitted with a high output two stroke engine. The USA has a very strong hovercraft cruising community and this has resulted in the evolution of a range of craft designed specifically for that purpose. The typical US design cruiser has a foam composite hull with a bag skirt, a propeller for thrust and a separate fan for lift and uses a small car or industrial engine for power.
What skills do I need?
I would have to say that if you have no DIY or engineering skills or aptitude then I would not recommend you try to build a hovercraft. Although the skill levels needed are pretty basic you do need to have some knowledge and understanding of machinery. You will need to learn how to lay fibre glass - not that difficult with a little practice. You will also need some basic woodworking type skills to cut and layout panels and build simple structures (you don't need to be a qualified carpenter - if you can assemble flat pack furniture without too much hassle then you should be OK)! Some basic engineering is needed to assemble the drive components - it's useful to have some knowledge of engines and simple mechanical drives. All is not lost if you feel you can't do some of these things - just ask for help in the hovercraft community or pay someone else to do them for you!
How much will it cost?
Depending on the actual design chosen, it could cost anything from about £1000 to £4000 upwards. A typical 2-3 seat cruiser hull should cost around £600-700 for materials. You then need an engine, the drive components (fans, prop, pulleys, etc) and a skirt.
Small new industrial or lawnmower engines can be quite expensive (£400-£1000 or so) so it may be better to choose a larger craft design that uses a small car engine - easily sourced from a breaker or scrap yard. Popular lightweight car engines include the Suzuki Swift and Subaru Justy. For large craft a Subaru MV pickup engine is also popular. The main criteria is to choose a lightweight engine that is durable and easily maintained. Almost any car engine can be used although modern engines can be difficult to install due the the need for the complete engine management system. Often it is simpler (and cheaper) to get an complete MOT failure or accident damaged car which then allows you to test the engine before removal and to strip the entire control system and wiring at the same time. With a car engine, you only need the engine, not the gearbox/clutch/etc. Some engines have the gearbox and clutch assembly integrated into the engine casing - these are obviously not suitable.
The fans used in almost all hovercraft are designed for use in air conditioning systems (MultiWing, Hasconwing, etc). Although not absolutely ideal for hovercraft, they do provide adequate performance and are easily available and relatively cheap. A typical lift fan should cost about £80 or so. Propellers are not easily available in the UK. The type used on hovercraft is usually the same as those used by microlight or ultralight aircraft. They can be bought from microlight manufacturers or distributors in the UK or imported from the US. Wooden core props can also be bought as bare cores or can be made from scratch (see the UH site for details). A typical prop should cost about £250.
The skirt material is readily available in the UK. Bag skirt craft use nylon or polyester reinforced PVC - otherwise known as truck curtain siding material! This can be bought from tarpaulin suppliers. Bag skirts are usually glued together at the joints using contact cement. Finger skirt craft use reinforced neoprene material - again readily available - and are stitched together. Material for a typical bag skirt should cost about £60 and for a finger skirt about £130.
How long will it take to build?
This an almost impossible question to answer! If you look at the plan suppliers web sites they give estimates of build times. Remember that they are just estimates - they are for the "average" skill level builder and don't allow for inevitable first time builder problems. A small craft could take about 200 hours to complete and a larger craft around 400 hours. Remember that if you do have a problem there are plenty of people who have probably had the same problem and are willing to help you quickly solve it.
What I've done
In the last three years, I have built three hovercraft. The links above are a rough record of the building process and the various problems and experiences I have had with each craft.
Which plans are best?
The UH plans are hand drawn, which makes them look a bit dated. However, they do contain all of the required information and don't have many errors. The Sevtec plans look CAD drawn but are actually produced using a graphics program - they look much nicer but the content and error rate is about the same as the UH plans. Both plan sets do not have every detail required to build a hovercraft - in some areas (like control cable routing for example), suggestions are made but there is no specific detail given. I would recommend that you also buy the (rather amateurish in presentation) videos offered by both companies - they contain many useful practical tips on construction. At the end of the day, the cost of these plans is insignificant in relation the cost of the materials needed to construct a hovercraft!
Which craft is best - UH or Sevtec?
There is no answer to this - each craft has it's advantages and disadvantages. They are all significantly different in size, power and performance. They all perform to the specification defined by the manufacturer therefore that is all you can expect.
The UH18 is a very fast cruiser capable of travelling comfortably at speeds in excess of 60mph - far faster than any UK style craft. The Scout is a very manoeuvrable hovercraft with amazing performance for it's power. The Prospector is a lower speed sea-going cruiser with high comfort level. For use in very small spaces (small narrow rivers for example), the Scout would be the perfect choice, for cruising long distances in sheltered water, the UH18 would be the winner, for comfort and rough water performance, the Prospector would be the best choice.