Wednesday, March 7, 2012

Explorer build

Here I go again It's the first of March 2012. The last build was a 16' Sevtec Surveyor and took me about 14 months to complete. This time I'm going for something a little bigger a Sevtec Explorer. This craft will have a flying width of 10 foot and it's length is 20 foot. Flying height is 15 inches. The craft on hover should be around 12 1/2 foot wide from the outer edges of the skirt.

I managed to find a workshop to build the craft in just 4 miles down the road from me. The building is a bit worse for wear to put it mildly and has no electricity, but it's under cover and secure, so what more do I need. I have had to do quite a bit of work to get the building inhabitable but after a few days spent boarding up & clearing up the mess that was strewn everywhere I was ready to begin.

It must be my lucky week as I mentioned to a neighbour that I will have to buy a generator for running a glue gun & sander etc and he said I have one in my shed that hasn't been used for a few years, and I was welcome to it it for free if I wanted it. So Monday evening was spent stripping the IC Briggs & Stratton 5hp driving the generator apart. Stripped the carb, washed out the fuel tank, fitted new spark plug, cleaned up the flywheel & magnet, put in a foam scouring pad as a temporary air filter. Put in new fuel and 6 or 7 pulls of the starting rope and it fired into life.  So now I have a 2kw genny.

I decided that because it is such a big craft I would build it on a jig to eliminate any discrepancies from any unevenness in the concrete floor. By Monday lunchtime 5th March I was able to start building the jig. The jig is very simple and made out of 3" X 2". The cross braces are 2.40 metres wide, which gives me a couple inches spare on each side. I have placed the cross braces at strategic points of the hull. I added 2 extra cross braces under the floor as I felt 112" between the front and rear of the floor panel was too large a gap to bridge. The hard hull of the craft will be 90" wide and 240" long

Anyway by Tuesday lunchtime the jig was built and ready to take the foam & GRP panels.

Pictures of the jig below:

Today 7th March 2012 I have ordered the foam core for the hull.  I have decided to use Tricast 6 PU foam.  The plan calls for 4.5lb density foam.  Tricast 6 has a density of 6lb and is approved by Lloyds for marine structual use so should be more than adequate for this application.  The foam has a 7 to 10 day lead time so hopefully it will be here by the end of next week.

I have also emailed several GRP suppliers today with a long list of items including polyester resin & CSM etc.  Last week I managed to buy a 100 metre roll of 200gram fibreglass cloth on ebay at a bargain price of £1 a square metre.

9th of March 2012, I have now placed the order for the GRP materials.  I had quotes back from two of the GRP stockist I emailed for a quote on the list of items I wanted.  There was a difference between the two quotes of over £130 including delivery.

I now have the difficult bit , waiting for all the stuff to arrive so I can start the build of my new toy.

Monday 12th March.  Over the weekend I had doubts to the amount of Tricast 6 foam I had ordered.  I had a funny feeling that I hadn't ordered enough.  I had ordered the amount listed for the explorer on the Amphibious Marines website.  I set about working out how many 25mm thick foam sheets I would need for panels (H6), H8a, side deck stringers H16.  I found that which ever way I cut & joined the foam I was going to be quite a bit short as the rudders used 3 x 600mm x 1200m, then there was the windscreen bolsters which would be approximetely another two 600mm x 1200mm sheets .  I then emailed Ian Speakman to see how many foam sheets he had used in his recent prospector build.  Turned out he had used more 25mm foam than was listed for the exploror and the explorer is a couple of feet longer than the prospector.

I am not going to use foam core for the rudders as I prefer foam/pvc board to make my rudders from.  I used foam/pvc for the rudders on my surveyor and I find they have many advantages over the rudders shown on the plans.  This means I can eliminate three sheets of 600mm x 1200mm tricast, but my order would still be at least 2 sheets short from what is needed.  I decided to order another four 600mm x 1200mm Tricast 6 sheets and four extra 12mm sheets to ensure I had enough for the build.  The postage for the foam to the highlands of Scotland is very expensive at £80 +20% VAT, so I would rather have a little bit too much foam rather than fork out another £96 delivery charge for one or two extra sheets.  I ended up telephoning Julie at Trident foams to increase my foam order by four extra  600mm x 1200mm sheets for the 25mm and the 12mm tricast 6 which is approx another £100 + 20% Vat.  At least I saved having to pay another expensive delivery charge.

While on the telephone Julie said that it is looking very likely that my order will be ready to be sent out tomorrow, so I may have my foam by the end of the week.

Friday 16th March 2012.  Today I had two large deliveries.  First one was from Trident foam, a pallet full of Tricast 6.  Not long afterwards a second delivery from Cornish Fibreglass Supplies, of resin & glass matt etc, which weighed in at 172 kilograms.  It has been a busy few days as we have workmen coming to fit external insulation on our house, so I have had to move my large shed, take down a lean to and a fence.  All stuff I could do with out right now.  I am hoping to start marking & cutting out some of the hull panels tomorrow.

Picture below of my two deliveries.  This is what the bare bones of a 20 foot Sevtec Explorer looks like:

Saturday 17th March:  Today I actually feel I have finally started on this build.  I cut out 7 of the panels.  These were H6 (floor), the two hull stringers, H8a & H8b, and two  H16 panels.  Next job is to glue the panels together then start fibreglassing.  I decided to do the longest panels first so I could use the jg to keep them flat while glassing them.   Four of these panels are nearly 20 foot long.  I also knocked up an 11 foot long X 4 foot wide laminating table, so I have somewhere to glass the smaller panels.

I am hoping to have the floor & the 4 longest panels finished before I go back to work on Wednesday.

Sunday 18th March 2012.  I managed to glue the foam together to form panels H8a, H8b & the two hull stringers.  I also cut out the relevent matt & cloth for these panels.  I was hoping to get the panels glassed but I ran out of time.

Monday 19th March was a cold wet & windy day.  I finally started to glass the panels.  I started with H8a & h8b.  I managed to get one side of them glassed before lunch, then I made sure that the two hull stringers were straight and used a few panel pins along their edges to make sure they stayed straight while applying the 200gram  glass cloth.  After lunch I glassed the two stringers on one side then glassed the other side of panels H8a & H8b.  I was hoping to glass the other side of the two stringers, but they were still a bit too green to take a chance on turning them over, so that is a job for tomorrow.

It is now April 6th 2012.

I have made steady progress with making and fibreglassing the panels.  My son had to be admitted for two weeks to a hospital near Edinburgh which is about 220 miles away.  This cost me some building time but he is well and home now which is the main thing.

So far I have finished 10 of the panels and have the two H9 panels glassed on one side ready to have the hard points cut out and filled with a putty made up of 300 grams of resin, 75 grams of 3mm chopped fibres, 30 grams of micro balloons and 4.5 grams of collloidal silica..  The plans show some of the panels have wood inserts along one edge which would be the upper skirt attachment.  I have decided that I am not using wood for this and I will use the hard point putty mix for the skirt attachment.  I will put the panel in place before cutting out these hardpoints, so I can make sure they are in the correct position.

I have been weighing the panels as I have finished them and comparing the weights to what was stated on the plans.  My floor panel came out 7 lbs over weight.  The other panels have either come out with weights as stated or slightly under.  Overall so far I am approx 4 lbs over weight,  which I feel is acceptable.

The floor panel I beefed up a little on the rear edge where the small panel is that the fan panel fits to.  The area is prone to damage if the craft is landed heavily, so I added another two layers of 450 grm CSM under the glass cloth.  This would account for some of the weight increase of the floor panel.

I have also found that since using a resin roller to apply the polyester resin, my panel weights are close to if not lower than weights stated on the plans.  I was using throw away brushes before to apply the resin, but the roller makes a much easier and better job, so worth the extra money. 

This was one of the first panels I had glassed, ready for final trimming & fitting.

Floor panel under construction

Floor panel completed.  This gives an indication of the size of the floor panel

The floor & fan panel (H1).  H1 is 89 inches wide.

Tuesday 1st May 2012.  I have been making steady progress with the build since my last post.  I have made all the lower hull panels in front of panel H1 (lift fan panel) and have started to assemble them.

rather than waffle on about what I have done during the build I shall let the following pictures tell the story to date.

Floor panel, H1 (lift fan panel) and H8 (lower bow panel) in position on the jig.

Panel H8 has been glassed into position.  The wood support frame has been screwed to the jig to ensure the panel stays in the correct position while the other panels are joined to it.

Panel H1 (lift fan panel).  The panel is supported by a temporary frame screwed to the jig while it is being bonded with fibreglass matt & tape to the rear of the floor panel.

Panels H1a & H15 can be seen in the background.  H1a has not been trimmed to final shape which will be done when panel has been bonded into position on the hull.

A closer look at the frame supporting H1

One of the 4 screws used to secure panel H1 to the sipport frame.  The two upper screws are within the lift fan duct area, so will be cut out at a later date.  The two lower screw holes will need filling and small glass tape patches bonded over them when the screws are removed.

View of the completed panels at this stage of the build.

H1a now in position and trimmed to final shape.  A support frame was also used as can be seen in the picture.

H8a upper bow panel now joined to H8.  Wood support frame screwed to the jig.

Close up of the framework sipporting H1 & H1a.

Uprights being screwed to the jig.  These will support the hull sides.

The angle pieces of ply screwed to the jig in this picture have two purposes.  Firstly they help keep the iprights verticle and in the correct position.  Secondly they are cut at the correct angle and height to supprt the lower hull side panels. 

Panels H7 are now resting in position on the jig ready for bonding to the floor panel.  No glue or other support was needed to keep them in the correct position.

View from the front of the hull.

View from front after the two bow side panels have been added.  All the lower panels have been bonded in position.

This is the join of the lower side panel to the floor in the lift fan chamber.  I have added extra layers of glass matt here and a layer of 200 gram glass cloth.  I felt this is a potential weak spot, so beefed it up a little.  This added approx 2 lbs to the weight, that I felt was a worthwhile penalty.  The glass cloth is 6 inches wide.

Another view of the lower hull looking from the lift fan chamber.

The two hull sides in position.  Only a few clamps needed to hold the panels in their correct position.  The port side in this picture has already been fibreglassed into position.

The hull deck stringers are put in place ready to be bonded to the hull.
View from the front

Side view of the hull

View of the hull from the rear.  This is as far as I have got with the build to date other than fibreglassing the two stringers into their final position.

Next stage of the build will be to make and fit the helm & bow panels.

Date 15/05/2012.  The past week I have had a lot of hours working on the hovercraft, but it doesn't seem like I have made much progress with the build.  I have ceviated away from the plans slightly by madding four support ribs down either side of the hull.  I feel these will add extra strength to the hull, give extra support to the upper side panel when being walked on.  They are also the starting point for some storage compartments, so the small amount of added weight I feel is well justified.

Upright support ribs

Panel along the bottom of support ribs to form storage compartments.

I have also made and added the deck bolster panels.  I still have to trim them to their final shape.

The metal drum in this picture is 16" high, which will give a good idea of how high the side are on the hull.

I have also started making the rear seat.  I have made & glassed in the rear seat panel and the arm rests.  I still have to round off the top edges of the arm rests then glass them in place. 

 Rear seat panel & arm rests

The arm rests have two main purposes:  Firstly they will add a little extra strength to the hull between the lift fan bay and the deck stringer.  The point just in front of the lift fan bay is a potential weak point as there is a lot of weight at the rear of the craft and again passengers in the front, so this area is a stress point.  I have also added an extra layer of 450 gram glass matt & 200 gram glass cloth to each side of the deck stringers in this area.

Second purpose is that the two fuel tanks will be housed under the rear seat.  As this craft will be fitted with a roof, I need air vents to the outside of the craft from the fuel tank area to stop any build up of petrol fumes, which could be disasterous.  The arn rests will hide the vents on the inside of the craft, but more importantly create chimneys either side of the tank area to guide the fumes to the outside.  To hide the vents on the outside and to stop water coming through the vents to the inside I have made up a plug and then a mould from which I can make two identicle vent covers..

I have also made a 370 round trip to Stonehaven to collect a Subaru Forrester.  The vehicle has done 94000 miles and still has several months tax & MOT left on it.   The engine when new gives out approx 125 brake horse power, so should be fine for the purpose I have in mind for it.  I shall be using the engine & ECU and associated wiring.  The radiator, heater & heater vents ect.  The rest of the vehicle will get scrapped.  I was hoping to use either the front or rear screen from the subaru, but they are too narrow.  The top of the hovercraft deck is 70 inches wide and the widest part of the Subaru screen is 60 inches, so I will have to think again about the craft windscreen.

Sunday, August 7, 2011

North West Highland Hovercraft Cruise - Summary

North West Highland Hovercraft Cruise

The North West Highland Hovercraft Cruise took place from the 23rd to the 30th July.

This was the first time this event had ever took place.  Three hovercraft attended the event this year.  There was a Sevtec Surveyor owned and built by myself and local to Lochcarron.  A Sevtec Prospector owned and built by John Robertson from Melrose.  The other craft was a Sevtec Vanguard owned and built by Steve Holland from Aberdeen.  There was also an enthusiast that drove up from Perth on the first Saturday of the event for a few hours.  He came out for a fly in my hovercraft for a couple of hours before returning home.  All three hovercraft are of a GRP foam core construction and are built from plans available from Amphibious Marine in the USA. 

All the hovercraft owners adhere to a cruising code of conduct set out by the Hoverclub. More details can be found on the Hoverclub website at


Hovercraft are probably the most environmentally friendly power craft that can be used on water.  They float on a cushion of air, so there is no rotating propeller in the water, which means that they do not create a wake in the water disturbing the sea bed or damaging the wild life.  There is no fuel or oil coming into contact with the water so they do not polute the water.  The biggest concern with hovercraft is noise, which is being addressed and modern hovercraft are much quieter than they were twenty years ago.  Hovercraft are unique in that they are able to reach places no other type of vehicle can. 

A question always asked wherever we go is, “Do hovercraft float if the engine stops?”  The answer is “yes” they do as they have ample buoyancy built in.  I regularly use mine as a fishing platform as it is very stable when floating.

The weather for most of the week was blue skies and sunshine, the only downside for some of the days being the strong gusty northerly winds.  The hovercraft were out exploring every day.  On Saturday 23rd July was only a short trip to the bottom of Loch Carron, as it was late afternoon before the first of the visiting hovercraft arrived.  On Sunday the three craft went out of Loch Carron and around the corner to Reraig and Loch Kishorn then flew around the point to Kyle and over to Loch Na Beiste on the Isle of Skye.  The wind was very strong and gusting to over 30mph; at one point we encountered waves of five foot plus high which all the hovercraft managed to negotiate safely.   

On Monday the winds were still quite strong, John and Steve flew to Plockton.  On Tuesday we started off by trying to sort my craft out as it was not hovering as well as it should.  We discovered the problem, so I spent the day sorting out my craft while Steve and John went exploring the area around Loch Kishorn.

On Wednesday the gusting wind had abated so we set off to explore Loch Alsh and Loch Long.  John and Steve flew their hovercraft around to Kyle of Lochalsh, but I decided to trailer mine to Kyle after the fright I had on the Sunday with the big waves going around the point.  This time I took my son with me while Steve and John took Dawn and Anne.  We flew to Eilean Donan Castle then under the bridge into Loch Long.  The route up through Loch Long is stunning.  We stopped on the Nonach salt marsh at the top of Loch long for our lunch.  From there we headed back to Loch Alsh and out to Glas Eilean.  Brandon & I decide to head back to Kyle, while the others flew on to Glenelg bay.

On Thursday it was overcast and the northerly wind had picked up again.  Anne & Dawn wanted to visit the West Highland Dairy shop at Achmore.  We landed on the beach below Achmore while Anne & Dawn walked to the dairy shop.  On their return we started to fly around to a quiet bay behind Plockton.  I turned back just before going around the point as the sea waves were getting beyond my comfort zone again.  The others continued on into the bay.

On Friday the weather started off overcast, but very light winds.  Today was to be a hundred mile sea trip for John and Steve as they flew their hovercraft from Lochcarron around the coast to Loch Torridon.  I decided I was not experienced enough to undertake the whole trip in my craft all the way around the exposed west coast to Torridon.  We landed on a small island above the Crowlin Islands and to the west of Toscaig.  We parted company here and John and Steve headed north to Loch Torridon while I followed the coastline back to Lochcarron.  I still managed a respectful 46 mile cruise along the rugged but beautiful coastline.

All in all it was a successful week and a good time was had by all.  We were made to feel welcome pretty much everywhere we went, although a gentleman in Lochcarron had a moan at Steve, which I felt was disrespectful and uncalled for!  I am hoping to host the event again next year where it is hoped more hovercraft will attend.

Photos and videos of the week can be seen on my website, as can other information regarding hovercraft at

Alan Wilkins (Lochcarron)


Sunday, June 26, 2011

BBV Hovercraft

North-West Highland Hovercraft Cruise 2011

The North West Highland Cruise will take place from Saturday 23rd July until Saturday 29th July.  This is a great opportunity to use your hovercraft in some of the UK’s most spectacular and beautiful scenery.  The North West coast of the Highlands has a wide diversity of landscapes and wildlife to explore. 

The regular wildlife we encounter includes seals, dolphins, and numerous species of birds.  The landscape varies from mountainous cliffs, rocky shores to golden sandy beaches.  This is not an organised event, but rather a get together of like-minded individuals pursuing their hobby of hovercraft cruising. 

There is no entrance fee and anyone with a cruising hovercraft is welcome whether it is just for a day or for the whole two weeks.  For your own safety, it is a good idea to make sure that your hovercraft is capable of operating in tidal waters and is in a seaworthy state.  Please adhere to the Hoverclub’s code of conduct to avoid unnecessary disturbance for local people and wildlife.  Remember that other people have to continue to live and work in this area after you have gone home.  Hopefully this cruise will become an annual one, so please use common sense when operating your hovercraft so this can be an enjoyable cruise for all concerned, and help it continue for future years.

There will be a voluntary curfew of using your hovercraft near to shore in Lochcarron before 09:00 or after 21:00.  The curfew is as mentioned is voluntary, but please remember that there are young children and elderly people living in the area that may be asleep in bed.  

Legal Stuff

As mentioned above this is not an organised event and is a group of like minded individuals getting together to pursue their hobby of hovercraft cruising.  I am not an event organiser or have any commercial interest in this cruise.  People attending the cruise are solely responsible for their own actions and conduct.  I am not financially liable for any damage, losses, or costs incurred by you or any of your passengers.  I am merely making lists of possible places to stay, launch sites and cruise destinations, as I already live in this area. 

I do not endorse any business or accommodation listed as they are only added to the lists to make it easier for any people wishing to attend the cruise find somewhere to stay and stock up with provisions if they need to do so.  Where you stay, what you do and where you go is entirely your own decision and at your own discretion.

Cruise Location

The main launch site will be in Lochcarron IV54 - which is situated in an area of outstanding natural beauty.  There are several free public places where it is possible to launch hovercraft from.  Below you will see them marked on the map.  There is a height restriction of 2 metres in Murray Square.  This is the most suitable launch site as there is a car park large enough for several vehicles & trailers.  This is a Highland Council maintained area and I am hoping to have access to the key for the height restriction barrier for most days of the event.  Once a month the car park is used by a mobile cinema, which would probably render the car park out of bounds for our use that day.  At the time of writing I do not know if any of the cruise dates will clash with the cinema.
There are two other possible public launch sites in Lochcarron, but neither as good as the Murray Square location.  There is a narrow dirt track leading down to the beach alongside Lochcarron golf course.  I have used this to launch from but it is quite awkward to reverse the trailer down, the beach is strewn with large rocks and the water can be a few hundred metres away if the tide is out.  I have used this site but I would suggest not taking a two wheeled drive vehicle down the track as the ground can get very soft. 

There is a concrete public slipway opposite the Lochcarron hotel.  The slipway is pretty straight, but only approximately 4 metres wide, with a drop of several feet either side.  The slipway is also tide dependant.  I would suggest the safest way if you feel you must launch from this slipway, is off a trailer as if launching a boat or unload the craft in the parking area and walk it down, as there is usually a breeze blowing across the slipway.

How to get here

Lochcarron is situated on the North West coast of Scotland.  For those of you with Sat Nav, post code is IV54 8XQ.

If travelling from the south, then personally I would use the A9 route rather than the A87, as it is a much better road for towing a trailer.  It is approximately 50 miles longer than the A87, but usually the quickest route.  The A87 is a more scenic route, so the choice is yours.

If you decide to take the A9 route or other routes mentioned below, then the following maybe of help:

From Perth take the A9 to Inverness, when entering Inverness continue forward over the Kessock bridge.  Continue for another seven miles to Tore roundabout.  At Tore R/A take second exit A835 (signposted Dingwall, Ullapool).  Continue along the A835 until the Maryborough R/A then the take second exit A835 Ullapool.  Continue forward for approximately 13 miles and you enter a village called Garve.  When leaving Garve village you continue forward for approximately half a mile and bear left at Gorston, signposted A832 Gairloch, and Lochcarron.  Continue forward to Achnasheen.  At roundabout take first exit signposted A890 Lochcarron and Kyle of Lochalsh.  Continue forward on this road for 18 miles until the junction of the A890 and the A896.  Take the A896 signposted Lochcarron.  This is straight on so do not turn at the junction.

From the East head for Inverness, then take the A9 North over the Kessock bridge towards Dingwall and Ullapool.  Now follow the same directions as if travelling from the south.

From the North take the A9 south to Tore roundabout.  At Tore R/A take the fourth exit signposted A835 Dingwall and Ullapool.  Follow directions as per travelling from the South.

North from Ullapool follow the A835 south to Gorston.  At Gorston turn right, signposted A832 Gairloch and Lochcarron.  Now follow directions as per travelling from the South.


For accommodation in this area check out my website where a list can be found of various types of accommodation, from campsites to hotels.  I am not endorsing any of the properties or businesses on my website but have compiled a list of them to make it easier for people wishing to attend the North West Highland Cruise find somewhere to stay.  I would advice that you book accommodation in advance as it can get quite busy in this area at this time of year with tourists. 

Food, fuel, & general supplies

Lochcarron has several places for eating out; these range from either of the hotels, riverside cafĂ©, and Juliennes bistro.  There are other hotels that serve food in Plockton which is a 7 mile hovercraft trip from Lochcarron or 22 miles by road.  There are also other restaurants in Strathcarron & Achintee - approx 4 miles drive from Lochcarron. 

There are two shops in Lochcarron.  The Spar is in the centre of the village and is open seven days a week.  This shop holds a wide range of groceries and stock they also have a hardware department upstairs.  They also sell petrol & diesel, which is on the opposite side of the road to the shop.  This is not self-service for fuel - pull in to the pump area and blow your horn.

The local post office can be found within the spar shop.

The other shop can be found at Lochcarron garage.  The garage is open six days a week, (closed on Sundays).  The garage also holds a wide range of groceries and stock.  They offer vehicle repairs and recovery.  The garage also sells auto gas, petrol and diesel, and also stock calor gas bottles.

None of the above is obtainable without money.  There is a branch of the Bank of Scotland at the bottom of the village opposite the shinty pitch near the Murray Square launch site.  They are only open three days a week - Monday, Thursday & Friday.  They also have a cash machine in the wall available 24/7.  Cash can also be withdrawn via bankcards from the post office in the spar shop, just ask at the counter.

Other places besides the two in Lochcarron for refuelling your hovercraft are in Kyle of Lochalsh.  You would need to moor in the harbour and walk approximately ¼ a mile to Morar garage, on the main road running through Kyle.  Another fuel station can be found at Broadford on the Isle of Skye.  The best advice I can give is make sure you have enough fuel before setting out on the cruise each day.


For your own and crews safety below are some safety tips.  These are in no way exhaustive and may not be relevant in/to every situation you encounter.  It is up to you (hovercraft captain/pilot/crew) to decide what is right or safe for you, your crew and craft in any situation you encounter

The weather is very changeable in this part of the world and can be calm and sunny one minute then be wet and windy ten minutes later.

Some common sense safety tips that maybe worth considering:
Ensure your craft is capable of operating in tidal waters, is well maintained and in a seaworthy state.
If conditions do become beyond your hovercraft or your own capabilities, I personally would seek shelter on the nearest beach or harbour, but it is at discretion what you do.
If going out on your hovercraft alone the common sense approach would be to tell someone where you intend going and the time you expect to return.
It is usually a good idea to wear a life jacket while operating a hovercraft on the water.
If you have one it is a good idea to carry either a portable and or fixed VHF radio.
It is probably a good idea to have a spare set of dry clothes on board, as hypothermia can set in very quickly when wearing wet clothes.
Other basics which are good to carry are a bottle of drinking water, smoke flares, fire extinguisher, first aid kit, and tow rope.

Map of intended cruise area

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:

How Does A Hovercraft Work?

So how does a hovercraft work?  The principle is pretty simple, in order to hover, a hovercraft needs to sit upon a cushion of pressurised air.  The tricky bit is to get enough pressure between the hovercraft hull and the surface of whatever it is you wish to hover over, to enable the craft to lift above it.  Not enough air pressure and the craft will not hover or not gain enough height to hover efficiently.  Too much air pressure will create excess water/dust spray from all around the craft.  A happy medium needs to be found.

To create the air pressure beneath the hull of the craft you need two things.
Firstly you need a way of generating the air beneath the hull.  This is achieved by using a multi-bladed fan, known as the lift fan.  Some small hovercraft use what is known as an integrated system to supply lift air but more on that later.  The fan is enclosed within a shroud which diverts the air beneath the hovercraft’s hull at a rate of many litres per second.  If we take a quick trip back in history to when Christopher Cockerell carried out his experiments with an air blower, set of scales and tin cans, he discovered by having one can inside the other and diverting the air between them air pressure was increased significantly compared to using a single can.


So drawing on this principle as a way to significantly increase air pressure, by forcing air through a restricted space we can generate enough through air that with the aid of another item called the skirt create enough air pressure that will lift the hovercraft hull above any surface.  Without the skirt not enough air pressure would be generated.

Now what is the skirt?  How does it work?  What properties does it need to have?

The skirts main function is to contain the correct amount of air beneath the hovercrafts hull, which will increase the air pressure to the correct level.  Although the skirt looks a fairly simple thing, its design is critical to enable the hovercraft to function correctly.  It also determines what height the hovercraft will travel above the surface.  As mentioned above too much air pressure and you have an excess dust/water spray depending on the surface you are operating on.  Not enough air pressure & the craft will not hover efficiently.

The skirt also needs to be tough enough to handle the rigors of everyday use and be flexible enough to follow the undulations of the surface the craft is travelling above.  In an ideal world all surfaces would be perfectly flat & level, but in reality they rarely are.  Usually the skirt is made of a vinyl type material as it is reasonably tough flexible and easily obtainable.

We now have a vessel with the correct amount of air pressure that is capable of hovering above the surface at a predefined height.  We now need a method to propel the vessel forward.  This is achieved in one of two ways.  Some small hovercraft use multi bladed fans set inside a shroud diverting the air flow to the rear of the craft.  This fan is known as the thrust fan.  These fans are usually around one metre in diameter.  This method is fine for smaller craft, but it does have its limitations.  Most commercially available small hovercraft in the UK  use this method to create sufficient thrust and is more than adequate and can propel small highly tuned racing hovercraft to speeds around 80 mph. 

Above I mentioned about the integrated system.  This is a way in which both the lift air and thrust are created by the same rear facing fan.  A portion of the fan duct is partitioned off to allow a percentage of the air generated by the thrust fan to be diverted beneath the hull to create the lift.

Diagram of an integrated system

The other common method of creating thrust is to use aircraft propellers as used on micro-lites.  This method uses a rear facing 2 or 3 bladed propeller at the rear end of the craft, as in the picture below.  The propeller is surrounded by some sort of guard for safety reasons.
Rear end of a Sevtec Surveyor Hovercraft fitted with a 2 bladed propeller.

It is all very well being able to hover and have a method of propulsion, but neither is of much use if you cannot control the direction the craft travels.  So we need a method to steer the hovercraft.  Steering the hovercraft is by a simple method of using rudders as used by early aircraft.  These rudders are connected to a steering wheel/handle bars at the front of the craft, by means of cables known as control cables.  By generating a large airflow across the rudders via the thrust fan/propeller, we are able to divert the air in either a left or right direction enabling us to steer the hovercraft.  The picture above shows the rudders on a Sevtec Surveyor hovercraft being test fitted for alignment.

To generate power to operate the lift & thrust systems of a hovercraft an engine is used.  Early small hovercraft used two stroke engines, but today most manufacturers have moved to using four stroke engines.  Four stroke engines are slightly heavier than two strokes, which is the main downside of their use.  On the positive side to using four stroke engines they are usually more robust and reliable, they offer better fuel economy and are much quieter than two strokes. 

Short Cruise