Author Topic: Builders Guide: Questions to answer before you start!  (Read 339 times)

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Ian Brooks

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Builders Guide: Questions to answer before you start!
« Reply #1 on: Aug 09, 2010, 3:07 am »
A builders guide to Cruising Hovercraft

 

There are two ways to own a hovercraft, buy one or build one. Buying a craft is of course the easiest way, although patience will be needed to find a good craft. Many people choose to build a craft - this can help with budget and can be a very rewarding experience, but can also be fraught with difficulties. I hope this will help to avoid the worst problems, but would encourage all potential buyers to make contact with the Hoverclub UK for advice and guidance. (www.hoverclub.org.uk).



Ian Brooks 2010



So you're thinking about building a cruising hovercraft?

What type of craft?

There are three main types of craft that are in mainstream use, known as 'Integrated', 'Twin fan' and 'Twin Engine'. These are described here:

Integrated
This is the simplest type of craft. A single engine drives a single fan that provides both the lift air and the thrust air. In some respects this is a compromise, and as one might imagine this results in some downsides. The advantage is of course is simplicity in mechanical construction, but the downside is that the craft will be a little noisier and consume more fuel than a similar twin fan craft.

This is a simple craft to operate and is recommended for beginners.

A homebuilt integrated craft based on the well known Osprey 1

Twin fan
This type of craft has two fans, or a fan and a propeller, driven by the same engine via shafts or belts. The advantage is that each fan can be design specifically for its purpose, making it more efficient and quieter. It turns out the the design of a fan for lift is different to the design of a fan (or prop) for thrust. The downside of course is the additional mechanical complexity involved in splitting the drive to the two fans.

This is also a simple type of craft to operate and is recommended for beginners.

A twin fan SevTec Scout, an easy first time build

Twin engine
This is similar to the twin fan design in that it has two fans (or fan and prop), each specifically designed for its proper purpose. However, each fan is driven by its own independant engine, which means that it can be controlled separately - which can be an advantage in some circumstances. This is the hardest type of craft to pilot and is recomended for expert pilots.

A twin engine SevTec Surveyor at Clevedon

How big should I build it?

The general rule here would be large enough for your needs. If you want to take passengers, then you might consider 12-14ft or larger. Sea-keeping abilities are directly related to size, so in this respect bigger is better, but if you will normally cruise 1-up then 10-11ft may be adequate. If you want to take to whole family, then you should look at 16ft plus.

Plans or own design?

Once the prospective builder has decided which type of craft to build, the next question is what design. Some might be tempted to design their own craft, but this is strongly advised against. Unless you are a professional engineer and have have excellent background knowledge, a home-brew design is unlikely to be work well. Remember, not only will this craft cost you several thousands of pounds and hundreds of hours to build, your life is going to depend on it.

We recommend that the prospective builder buys a set of plans and sticks pretty rigidly to them. Minor cosmetic changes are usually fine, so you can customise your craft to suit yourself, but al structural and functional parts should be constructed per the plans.


Where can plans be obtained?

There are several places where good plans can be obtained. A good set of plans is an investment, and the few pounds these cost will pale into insignificance compared to the overall cost of the build so don't skimp. If you're unsure which craft to build, buy several sets of plans and then decide. There's nothing worst than completing a craft only to find out it does not do what you wanted it to.

SevTec
The SevTec range of craft are wel proven in the home-build area, and there are several excellent examples in the UK. These craft do not look pretty, but they work exceptionally well, are safe, capable, and well designed. Plans can be ordered online, along with quirky instructional build videos - these are highly recommended, they will pay for themselves by the avoidance of waste from silly mistakes!

http://www.sevteckits.com

A SevTec Vanguard and Prospector on the Clyde

Universal Hovercraft
The UH line of craft are also well proven in the home build market, but have less acceptance in the UK so far. Several have been built, they are very fast but lack the "all terrain" abiliy of the SevTec machines. The larger craft (UH18 plus) are not really suitable for beginners, but the smaller machines are. Plans can be bought here:

http://www.hovercraft.com

A UH18

ASV Superwedge
This is an Australian design for an integrated craft. Several have been built in the UK and the craft has been successful.

http://www.asv-aust.com/products/kitplans.htm

ASV Superwedge "HOW MUCH was it??? Not very much, dear, quite cheap really"

UK Plans
Unfortunately there are no home-grown plans available that can be recommended - this is a bit sad considering that the UK is the home of hovercraft technology! The HCGB offer the "constructors guide" but this is not recommended as the design is very old and it does not result in a craft suitable for cruising.

What budget should I allow?

The cost of building a hovercraft varies tremendously, depending on the specification of the craft, its equipment, its size, etc. It is essential that a suitable budget is available if the build is to be successful, and as guidance one might expect to spend in the region of 3000 - 5000 for a medium sized (around 14ft) craft. The good news is that this amount would be spent over the course of the build process, so it does not need to be found all at once.

We find that the cost of similar builds will vary tremendously from builder to builder. This depends largely on how much the builder does himself, on the standard of the build, and how much he has done for him, which of course also impacts on the total build duration. Fast builds tend to be expensive!

When I built my craft, I stopped adding up the cost after it first hovered, since any further spend was "maintenance"!!!

How long will it take

Most people take between 12 and 18 months on the build. This might typically require one day per weekend and an hour or so most evenings. It can be done a lot quicker, of course, if more time is available, or if more work is sub-contracted out.


What are the main construction methods?

There are three main construction methods available to the home builder.

Traditional Fibreglass
For most home builders this means purchasing a finished hull from an established manufacturer and then completing the build. In most cases, other major components will also be bought making this really a kit assembly rather than a true homebuild.

"Freedom 1" hull as delivered to the home builder

Foam-fibreglass composite
This is the build method adopted by the Sevtec range. It is suitable for unskilled persons, and most beginners find it relatively easy once the basic techniques are mastered. In addition, basic metalwork skills and some wiring will be needed.

A foam composite SevTec Surveyor lower hull during build

Wood
The ASV is built from marine plywood, which is an advantage for this already skilled in woodwork. The UH range are also constructed extensively from wood (in addition to some fibreglass work).

ASV hull under construction

What skills and facilities will I need?

A hovercraft can be built by anyone with well developed DIY skills. It helps to have some understanding of mechanics and of electrics such as might be needed for car maintenance, but the build can be completed without these - that's what the Club is there the help with. Most of the specialist skills such as fibreglassing can be learned fairly easily by a competent handyman.

The builder will need a dry and fairly large workshop or build area - a domestic garage will suit craft up to about 12 or 14 feet. It is possible to build hovercraft in temporary buildings or even tents, and one noted Dutch gentleman built his in his attic and had to hire a huge crane to bring it down when it was finished! The level of workshop equipment needed will vary with the type of build, but you should allow some of your budget for tools.

Where can I find on-line suppliers?

There is an extensive list of useful parts suppliers in the Forum, here

Don't forget the Club Discount Zone where you could save hundreds on a typical build!

A list of hovercraft plans and kit suppliers can be found here

Join the Club!

The Hoverclub is here to help you make the right choices, and to assist as you move through the build process. You'll get personal advice from members via our builders forum, and access to the collected knowledge stored in our technical information section, here. Joining will be the single best investment you will make! See you soon!



Ian Brooks
August 2010
« Last Edit: Aug 18, 2011, 1:13 am by John Robertson »

 

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