Sunday, June 26, 2011

An Carranach Article (Published March 2010)

Recently there was an unusual vehicle travelling on the water of Lochcarron.  It was a 16 foot hovercraft.  The hovercraft had its maiden voyage on the Loch on Saturday the 12th Dec.  Ironically it was 55 years to the day from when Christopher Cockerall the inventor of the hovercraft, patented the original hovercraft design.

The hovercraft is a unique vehicle, as it is capable of travelling on land, water, snow & ice.  The hovercraft floats above the surface on a cushion of air contained within its surrounding skirt.  This means that there is no friction between the hovercraft and the surface of whatever it is travelling over making it capable of operating in areas that are out of bounds to other types of vehicles.  The hovercraft is also capable of floating like a boat, so can be used for fishing.  The hovercraft also has its limitations because of the air cushion on which it travels, as they don’t work very well on slopes or in strong winds.

The hovercraft in Lochcarron was built by a local ambulance crew member in his spare time.  The hovercraft was built from a set of plans purchased on the internet from a company called Amphibious Marine based in the USA.  Amphibious Marine, owned by Bryan Phillips bought the manufacturing rights a few years ago of the Sevtec range of hovercrafts, from a man called Barry Palmer.  Barry Palmer was an aeronautical engineer, who back in the 1970’s designed the Sevtec range of hovercrafts in his spare time.  There are seven different hovercraft in the Sevtec range.  These hovercrafts are of various size & can be built using various engine sizes.  The smallest hovercraft in the range is called the Scout, which is 11 feet long and can be powered by a 12 horsepower lawn mower engine.  The largest craft in the Sevtec range is called the Mariner which can be built up to 28 foot long, carry up to 16 people and powered by a car engine. 

The hovercraft in Lochcarron is a Sevtec Surveyor.  This hovercraft design can be built in two different sizes, which are 14 & 16 foot long.  There is very little difference to building costs between the two sizes.  The 16 foot version was opted for as this gave a bigger carrying capacity, but more importantly more buoyancy making it a safer craft for use in open water.  The Sevtec Surveyor can be fitted with a range of engines.  It can be powered by a one or two engine configuration.  With a two engine version, an engine of approximately 12 hp would be used to supply the lift and another engine of approximately 18hp to 22 hp for driving the thrust propeller.  The Sevtec in Lochcarron is powered by a 35 hp Briggs and Stratton engine. 

The 35hp engine drives both the lift fan and the thrust propeller via a series of pulleys and belts.  The lift fan is a 2 foot diameter nine bladed air-conditioning fan, which are readily available in the UK.  The thrust Propeller was Imported from the USA, as there are no manufacturers of suitable propellers in the UK.  The thrust Propeller is a 2 bladed 72 inch composite aircraft propeller.  It is the propeller that gives this hovercraft its distinctive sound similar to an approaching helicopter.  Hovercrafts have had a bad reputation in the past for being very noisy.  This was largely due to the use of high revving 2 stroke engines and inefficient thrust fans.  There is still some work to be done on this hovercraft as regards to reducing noise levels.  During the winter months a new exhaust system will be manufactured & fitted, which is hoped will reduce noise levels even further.  Noise levels are already below the HCGB acceptable levels.

The hull of the hovercraft was built from a foam cored fibreglass sandwich.  This is a very easy way of building otherwise complex structures.  The foam used is not the beaded white polystyrene type of foam, as this would not be strong enough and polyester resin dissolves it.  The foam used is a high density foam used amongst other things for marine applications.  This foam offers exceptional strength for little weight gain.  The hull is made up of a lot of smaller panels which are later bonded together. 

To make the hull all the separate panels are measured and drawn onto the foam sheets.  They are then cut out using nothing more than a straight edge and sharp craft knife.  Each foam panel is then fibreglassed on both sides.  These panels are then trimmed again to the correct size & joined together with fibreglass tape.

The skirt is made from vinyl covered polyester as used for making banners.  This vinyl material is easy to obtain, reasonably cheap but more importantly easy to work with and repair.  The skirt looks quite complicated, but when broken down into individual pieces is again, fairly straight forward to manufacture and fit.  The skirt is made from several pieces, which are then glued together using a special contact adhesive. 

The hovercraft was built using all new parts and has taken approximately 14 months to build.  The hull materials, engine, & propeller were the biggest single monetary outlays, but it was the smaller and seemingly insignificant items that soon sent the cost of the craft over the initial budget.  

This hovercraft is going down to the Isle of Wight in April 2010 to take part in a planned event to cruise around the island.  There may be a similar event held on the North West Coast of Scotland in the Summer 2010, (subject to correct permissions & insurances being gained).

Hovercrafts are becoming more popular these days.  There are basically two types of hovercraft.  There are cruising craft such as the Sevtec range, which are used for exploring & fishing etc.  There are an increasing number of cruising craft in the UK as this form of hovercrafting is growing in popularity.  The other type of hovercraft is the racing craft.  Hovercraft racing is very popular in the Southern half of the UK and Europe, but no hovercraft racing events are held in Scotland.  Racing craft can reach speeds of up to 80mph.  Racing craft are not suitable for use in deep water, as they are built with very little inherent buoyancy.  The 2010 world hovercraft racing championships are to be held in August at Towcester in the UK.

If you are considering a hovercraft, the first thing you need to do is decide what you will want to use the hovercraft for, (cruising or racing).  Then you need to gather as much information and advice as you can on the different types of hovercraft & manufacturers.  It is possible to buy new “ready to go” hovercraft from several hovercraft manufacturers in the UK, or there is the self build option, such as the one in this article.

A good place to find out more about the different forms of hovercrafting is from
The Hovercraft Club of Great Britain.  Their website and members have been very helpful with advice while building the above hovercraft.

HCGB web address:

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