Why have a skirt? All modern hovercraft - large and small - use a skirt of one sort or another for their suspension system so that the power required to lift the craft can be minimised.

A hovercraft skirt is required to fulfil the following functions:

Contain the cushion of air beneath the craft at the  required hoverheight. Have the ability to conform or contour efficiently over obstacles so as to keep

to minimum, the loss of cushion air. Return to its original shape after having been deformed. Give adequate stability. Offer little resistance to the passage of obstacles beneath it. Have the ability to absorb a large proportion of the energy which is produced

on impacts or collisions with obstacles greater than hoverheight or cushion depth

A hovercraft skirt should have the following features:

Be easily maintained on site without the need to lift or jack-up the craft. Have a long operating life. Be relatively simple to make and fit. Have a low maintenance cost.  The initial cost of making the skirt may not be

very low but it is important that once made and fitted, the skirt be cheaply maintained.

Be tailored so that it is even in height above the ground all the way around the craft.  One part of the skirt should not drag whilst another is 20 or 30 millimetres above the ground.

SKIRT DESIGNS

There are several major designs of hovercraft skirts but only the three main types will be presented in the  following pages. Each has its own applications.  

 The bag skirt

 The finger or segment skirt  

 The bag and finger skirt

HOVERCRAFT SKIRTS 

The stability of a hovercraft is dependent upon the pitch (fore and aft) and roll (side to side) stiffness of the air cushion.  This stiffness is derived from two main sources:

The bag skirt employs an inflated bag surrounding the air cushion and it is the pressure of the bag which provides the stability.

All three designs use the movement of the centre of pressure on the collapse of the skirt to provide stability, ie., when the skirt crumples as the edge of the craft drops, the effective contact point where the skirt touches the ground moves.  There fore extra cushion area and thus more lift is provided at that side, moving the centre of lift pressure over and tending to raise the craft to restore it to a level position.

DESIGN SEQUENCE

The first action when designing a skirt is to decide upon the main use to which you will put the hovercraft and the type of terrain over which you intent to operate it.  For a cruising craft that will be operated over water you will probably opt for the smooth but stable ride of the bag and finger skirt.  If you fancy yourself as the driver of a racing hovercraft you may choose the full finger skirt which has very low drag characteristics or maybe a straight bag skirt if racing on terrain  where hull damage would otherwise occur if a soft skirt were used.   The next step is to develop  a section through the side skirt geometry, deciding where to put the hull structure to pick up the skirt and remembering the hydro-dynamics of the hull form.  The skirt and the hull shape must be designed together.  Finger skirt hulls generally have rounded corners whereas those fitted with bag skirts usually have square or angular ones.  At this point in designing a hovercraft a great deal of variation in the exact shape and size of the skirt and structure can be considered until the happy medium is found.  The bow shape can now be developed in

a similar way. The final stage is the development of the tailoring, splitting it into a sensible number of panels which, when sewn or glued together, adopt the shape required.  These panels should be sufficient in number to enable the skirt to look smooth and free from stress when it is inflated.  There should, however, be few enough panels to make construction of the skirt fairly simple and straightforward.  Finally, you must decide on the type of material.

Skirt Designs

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Here we will give specific instructions on how to make a wall skirt, and we will briefly explore into other types of skirts

As far as Hovercrafts go, there are three types of skirts to be concerned with: Bag Skirts, Wall Skirts, and Finger Skirts. Type I hovercrafts generally use Bag Skirts, Type II (our type) use Wall Skirts, and Type III large-scale professional hovercrafts for racing or recreation usually use finger skirts. You can mix and match the type of skirt with the type of hovercraft you're making, but as for now we've only tested Type I with a bag skirt and Type II with a wall skirt. As so far we don't know how to construct a Finger Skirt (they're really complicated), but down at the bottom of the page is a brief explination of what one is and how they work. 

* IF YOU ARE MAKING THE SAME AS OUR HOVERCRAFT (type 2), ONLY THE WALL SKIRT WORKS. A finger/segmented skirt or real bag skirt requires the frame to have a huge air chamber built in and a ton of stuff that costs a ton and takes a ton of time, and a bag skirt like the one on hovercraft 1 doesnt work too well. 

BAG SKIRT (Not like the ones on a racing or recreation hovercraft, but for one on a cheap homemade one): 

HOW THEY WORK: 

A bag skirt is like an intertube with a piece of plywood on top, holes feeding into the middle, and an air supply. When it inflates its the same principle as simply sitting on a O-shaped ballon, since that's essentially what it is. 

Air goes into the bag, inflating it so it is about two inches high. The air inflating it goes out the holes located towards the center, making the air also build up pressure in a chamber between the ground, the plywood, and the inflated ring of the bag skirt (plenum chamber). The pressure eventually buld up

Our Hovercraft

A bag skirt floating

The bag skirt with a disc mounted in the middle

enough so that it and the bag skirt is lifting the plywood, and the air slides out underneath the bag, creating a nearly frictionless environment. 

HOW TO CONSTRUCT A BAG SKIRT: 

This depends on what you're using the bag skirt on. If you're constructing a Type I circular, you'll want the bag skirt the cover the whole bottom, mounted in the center with a disc. This makes the skirt sections around the center inflate in a donut shape, carrying the outsides of the craft. 

You will want a thick sheet of plastic, nylon, or other air tight and durable material. (trash bags have been known to work, but we cannot confirm this.) This sheet has to be at least two feet bigger than your craft. lay your craft on top of it. then take the corners and sides of the sheet and fold them up onto the top of the craft. Make sure the skirt has enough slck to inflate, becuase if it has none it wont lift. Or it will explode. Then staple the skirt onto the plywood in lots of places, and duct tape it a lot to the top, making sure no air can get out. Then attach your coffee can lid. Cut six holes about 4 inches away from the edges of the lid, and a little more than one inch in diameter. The reason the holes in the skirt need to be closer to the center is so that the air doesnt immediately go out of the bag and away from the craft, but goes into the center where the bag contains it like walls, and it lifts the whole thing up a tiny bit for the air to slide out. 

NOTE: We have not guarantee this skirt to work on a type two craft. 

On a Type II hovercraft you want to go ahead and have the piece of cloth be mounted in a donut shape. This means you're going to need a long straight piece of material (make sure it's thick enough by holding the sides of it and seeing how far you can push it down. You want at least 5 or 6 inches of slack without having to mount the two sides too close together) and you're going to mount the outside edge of the cloth in a oval around the outside of your hovercraft, and the inside edge in a smaller oval further inward on the bottom of the hovercraft. We reccommend that you first staple the skirt in place, then when you know its in the right place, seal it tight with caulk. Make sure you leave enough slack so that it has space to inflate, but don't

hovercraft from xinventions.com

make a skirt thats TOO loose. Just like in the Type I hovercraft, you'll need to space small holes on the bottom of the skirt to let air escape. 

NOTE: We DO NOT reccommend using a bag skirt on your 8-by-4 Type II hovercraft because we HAVE NOT tried it before! If you try, you're doing so at your own risk of failure. _________________________________________________________

WALL SKIRT: (not generally used on high performance hovercrafts because disadvantages in repair capabilities and terrain handling capabilities. 

HOW THEY WORK: 

Wall skirts hang down from the edge of your hovercraft (hence the wall name). The skirt inflates and pushes outwards, so the hovercraft rides on a cushion of air. It's like an electric inflating matress, if the bottom was cut out of it, and a piece of plywood placed on top of it, the matress would still inflate, but when it was fully inflated some air would pick it up still a centimeter more so it could slide out from underneath. A good bag skirt is like a wall skirt that uses an inflated wall to contain the air. 

HOW TO CONSTRUCT A WALL SKIRT: 

Find some airtight (make sure it's airtight before hand!) material to use for your wall skirt. Next, get enough material to fit around the outer edge of your hovercraft, and remember to always get a little bit extra. If you're constructing an 8-by-4 hovercraft like we did, we recommend making your skirt around 13-17 inches tall, but make sure it stays the same height all around. If you notice that the material you're buying comes in heights more than twice the height you want your skirt, just go ahead and buy enough so you can cut it up and sew different pieces of the skirt together. This is what we did, since we bought a 9-by-5 foot piece of material, and cut it up into three skirt segments that were each 15 inches tall and 9 feet long. We then sewed these pieces together, and double stitched them just to be sure. So you have a long material that is about 15 inches wide. If you just put this on the hovercraft the skirt

A wall skirt doing its job

The bottomside, with top edge of the skirt mounted and bottom edge of the

skirt pulled tight.

Hovercraft from xinventions.com

would just flap out, so you need something to hold it. A rope is then attatched to the bottom and pulled tight. Make sure to use a strong rope that is braided rather than wound, so that if one part breaks it doesn't all fall apart. (We used a thick nylon rope for Home Depot) We folded an inch of the skirt over the rope and sewed it to itself to make a pocket. some people fold the skirt over the rope then duct tape it. But make sure that you make it with the rope already in it, and knot it so it doesn't slip out. 

The top edge of the material is mounted to the edge of your hovercraft, and the bottom end should have a rope strung through it (take the material, put the rope on it, fold it over the rope, and sew the material on itself to create a slot for the rope to be in) to keep it tight. This keeps the bottom of the skirt from flapping outwards, so it will inflate. Cut the skirt so that you have an inch overlapping and sew it by hand. tie the rope, pull it tight and burn the ends to prevent fraying. 

If your hovercraft doesn't inflate, try pulling your rope tighter. Before you finally cut the rope and seal the knot, try to make sure you haven't pulled your rope too tight, not allowing enough slack. Any part of the rope (like the knot) that's going to drag across the ground should get covered in something to protect it, like duct tape. 

FOR EXTRA PROTECTION: Cover the part of the skirt that drags on the ground (the section that the rope is strung through) in duct tape or some other strong material so the sewing doesn't come undone and the rope doesn't come out. 

FINGER SKIRT: 

HOW THEY WORK: 

Finger skirts are used on professional hovercrafts. A finger skirt has tons of little segments that each individually inflate that conform to the ground so the hovercraft can go over all terrain. Professional finger skirts are generally made out of very strong rubber material. The fingers are actually a bunch of seperated "little skirts" that inflate independantly. To build a finger skirt, you need a large hull with a built in plenum chamber and that takes a lot of work. 

A professional finger skirt

A FINAL NOTE ABOUT SKIRTS: 

When picking a material, make sure it can take a lot of wear and tear. Keep in mind this material is going to be dragging along the ground a lot, and needs to be able to maintain it's air tight manner.

THE BAG SKIRTDescription. The inflated loop consists essentially of a tube of material (similar in a way to a car inner tube) which is inflated at a slightly higher pressure than the air cushion beneath the craft and this is achieved in one or two ways:

The full flow system feeds all the lift air into the skirt and from there through small holes in the inner skirt wall into the cushion.  By controlling the number and size of the holes it is possible to alter the pressure differential between the loop and the air cushion.

The no-flow system pressurizes the loop via small scoops at the tip of the lift fan. The size of the scoop is about 10% of the total lift fan area.  The skirt is sealed and does not have any exit holes since most of the air is fed directly into the cushion.  Even small tears in this type of skirt can, however, lead to considerable loss of skirt pressure which in turn could result in dangerous instability.

Skirt Characteristics. The bag skirt is fairly simple to design and construct but gives a harder ride than the segmented type and has more limited obstacle clearance, depending upon the pressure differential between the loop and the air cushion.  Usually it gives fairly high drag over undulating surfaces.  The inflated loop skirt is very stiff in roll and pitch.THE BAG SKIRT CROSS SECTION. To design the cross section, the height must first be established and this should be about one eighth of the craft width. The cross section of the bag is comprised of two radii, the outer curve and the inner curve. For simplicity it can be assumed that the ground contact point is directly beneath the outer extremity of the hull and therefore the outer radius is equal to half the distance between the ground and the upper fixing point. The ground contact point can in fact be positioned fractionally in from the outer hull edge but for the sake of stability, it must never be outside. To design the cross section, make a scale drawing of the craft lower hull at the appropriate hover height and draw in the outer semi-circle. The radius of the inner circle is calculated by multiplying the outer radius by a factor given in the following table.  

Pressure Differential bag pressure / cushion pressure

Factor Inner radius / outer radius

1.2 : 1 6.0

1.3 : 1 4.531.4 : 1 3.51.5 : 1 3.01.6 : 1 2.661.7 : 1 2.431.8 : 1 2.25

The choice of pressure differential is based upon the degree of stability required.  The higher the ratio the greater the stability, but at the expense of undulating surface performance and higher skirt wear on uneven terrain. After calculating the inner radius, draw in the inner circle.  This will give the inner skirt fixing point and note that the changeover from the small radius to the larger radius is at a point 15 degrees in from the ground point. The skirt cross section calculated in this way has balanced geometry and will automatically take up this shape, provided that the pressure differential is accurately predicted. THE BAG SKIRT - BOW SECTION An ordinary side cross section at the bow would be very prone to plough-in problems, therefore the bow section is usually designed with a less bellowed outer curve.  This shape however, does not have balanced geometry and so it will not automatically take up this shape but must be forced to do so by the tailoring.  The inner curve has the same radius as that of the side cross-section, but the outer radius is now centered on a point retracted well in from the leading edge of the hull.  This is quite acceptable if the bow corners are tapered back, thereby providing a number of joints  where the skirt can be forced into this shape. If the bow is straight with square corners, the long front panels of the skirt will not adopt this shape and will tend to round out.  To overcome this problem, the bow skirt will need to be designed with balanced geometry which means using a much larger inner radius. To layout this cross section, center the outer radius at a distance equal to  r x 0.85 in from the leading edge and maintaining  a hover height of 1/8 hull width, use an inside radius equal to r x FACTOR as  used in calculating the side cross section - see table below.  

Pressure Differential bag  pressure / cushion pressure

Factor Inner Radius / Outer radius

1.2 : 1 6.01.3 : 1 4.531.4 : 1 3.51.5 : 1 3.01.6 : 1 2.661.7 : 1 2.431.8 : 1 2.25

The disadvantage of this skirt is the large overall width of material. As well as very high wear on uneven terrain around the ground contact line. Even if you can patch several times your bag skirt you will need to replace him once the patches produce major wrinkles in the lower section ( 3" inner and outer of ground contact line ). THE BAG SKIRT - PERIPHERAL JETS The bag skirt requires a number of holes on the inner fact to transfer air from the skirt to the cushion.  These holes vary in size but are generally 3 - 6 inches in diameter. The total required area of these holes can be calculated using the following formula:  

A  =             Q      20 X        Pb x Pc

Where A  = Total area of peripheral jets (sq. ft)       Q  = Air Flow                      (cu ft / sec)       Pb = Pressure in the bag           (lb. / sq. ft)       Pc = Pressure in the cushion       (lb. / sq. ft)

Cut about 90% of the calculated number of holes and then slowly cut out the remainder, checking regularly the relative pressures with a simple water manometer until the required differential is obtained.  Holes should only be cut in the bow and side sections of the skirt. No holes should be cut in the rear section as this can cause water scooping.SKIRT TAILORING Once the skirt cross-sections have been worked out you have to decide how to cut out all the panels of material and assemble them so that the skirt will adopt the required shape. Tailoring of skirts is quite an art and can be approached in two ways; one is by employing a mathematical method and the other is by using a system of templates. THE BAG SKIRT  The Mathematical Method: To begin, scribe marks around the skirt circumference at intervals of 100 mm, starting from the inside edge.  These marks will be the contour lines.  Measure the horizontal distance from the outer skirt fixing to each of these contours. These contours now have to be plotted on a scale horizontal plan of the craft. Each contour line should be drawn its respective distance from the outer fixing. The method to calculate a rear corner by drawing lines along every side. To design a piece of material from AA' to BB', draw a 'line (xy) midway between AA' and BB' at right angles to the body.  On a piece of skirt material, put a line XY and draw contour lines at right angles to it and at 100 mm intervals. Measure the distance between the AA' line and the xy line along each of the contours and transfer the distances. For example, the distance between xy and AA' along the 900 contour is 300 mm, therefore put a mark 300 mm from XY on the 900 contour and repeat this for the xy to BB' distances.  When this has been done for each contour line, link the marks and you will have the shape for the panel.  When cutting out the panel, allow a 20 mm margin to allow for sewing and gluing.  To make up the skirt, pin the two adjacent panels

together along the sewing line and sew several times for strength. Calculating the bow. The same techniques can be applied for the bow as that used for the other skirt sections. This is done by taking 100 mm contour points around the bow section and plotting these on a scale horizontal plan of the craft together with the side contours. The Template method. Cut out a number of full-size templates of the required size from stiff cardboard or plywood.  Turn the craft hull up - side down and affix the templates in position.  Place the skirt material over the templates so that it adopts the proposed shape of the skirt.  Where pieces of the skirt meet at the joint, they may be joined together with pins and subsequently sewn together as described in the mathematical method.   Or try to make a mock up from your finally skirt shape in foam - mark all different angles ( attachment panel to panel  )  and copy to cardboard. Lay cardboard on skirt material and transfer shape - allow again at least 20 mm for sewing and gluing panels together. Check shape on your foam mock up and continue.

THE FINGER SKIRTThe finger skirt is comprised of a large number of separate segments which are able to slide and bellow individually to conform with the shape of the water surface or terrain over which the craft is traversing.

The fingers should not be sewn or connected together in any way or else the design of the skirt which is to form a very flexible air seal between the hovercraft and terrain, will be defeated. To achieve this, the fingers should only be attached to the craft by a rigid strip along the upper edge and by some from of corner tie at the two innermost apexes. The straight finger serves well as a bow skirt due to the advantageous receding angle of attached which helps in riding over waves and ground undulations and at keeping frontal spray and dust to a minimum.  The straight finger however, is very unforgiving to being dragged backwards over obstacles.  The extended finger is best used at the side and rear of the hovercraft as it has a better obstacle clearing characteristic and also its design helps to maximise the effective cushion area because the ground contact point is much further out towards the hull perimeter than for that of the straight finger. The inner fact of the finger skirt is completely open which means that apart from a very marginal increase in pressure due to the peripheral jetstream, is a very soft and flexible with only actual cushion pressure holding it firm.  This is  vastly different to the bag skirt which has a peripheral pressure much greater than cushion pressure.  The finger skirts at the rear of the hovercraft must be equipped with either a single antiscoop flap or for improved flexibility, individual strips may be sewn to the inner edges of each finger which extend out belong the ground contact point.  This reduces their efficiency  in retraining cushion air from escaping, but unfortunately is quite essential if the hovercraft is to be used anywhere than over smooth terrain.CHARACTERISTICS OF THE FINGER SKIRT The straight finger skirt is easy to design and construct and repair work is also easy

because of the small size of each segment.  The extended finger however is a little more difficult to design . The finger skirt, straight or extended, gives a very smooth ride and has a low friction characteristic and so long as the cushion height is adequate,  is ideal for travelling at high speed over waves and rough ground.  Apart from the rear fingers which should have an anti-scoop flap, a hovercraft with a finger skirt does not trap water like a bag skirt at lift off.  An extended finger uses a great deal more material than a straight finger or bag skirt and for this reason, it has become common practise for the expensive low friction neoprene coated fabric to be used only on the knuckle which constantly rubs across the on-coming waves and for less expensive non-coated fabric to be used on the bellow and sides of the finger. To construct a Straight Finger Skirt. Straight Fingers are best used at the bow of a hovercraft. To design a straight finger you must draw the cross-section of the skirt under the bow and make a paper template to this shape.  Draw a rectangle of width equal to half the hoverheight and of height equal to the skirt length from the nose of the hull to the ground contact point.  Duplicate the cross section pattern and lay these alongside the rectangle. Allow for a seam at the top of the rectangle and then using this completed shape, make a full template out of plywood. To make the skirt, simple mark around the template and cut out as many fingers as are necessary to evenly fit across the bow of your hovercraft.  TO CONSTRUCT AN EXTENDED FINGER SKIRT. Extended fingers are best used at the side and rear of the craft although it is common practise to use them as bow fingers also, in lieu of the straight finger which has a set back ground contact point.

To draw a development, you must draw the cross  section of the skirt under the bow and make a paper template to this shape.  Next draw a rectangle of height equal to the straight fore edge of the cross section and of width equal to half the hoverheight.  Transpose the cross-section shape along both sides of this rectangle  and then draw in two smooth curves from the centre of the top of the rectangle out to the outer hull contact points of the two adjoining skirt cross-sections.

The extended skirt knuckle is developed by extending two curved lines upward from the centre of the top of the rectangle to intersect with a horizontal line equal in width to half the hoverheight and at such a height that the distance along the outward radiating curves is exactly equal to the upward radiating curves.  The lengths of these curves must be equal as they represent the common stitch lines on the finished finger and the hull contact point on the cross-section shape and the top of the knuckle must come together at the same point.  Allow for a seam at the top of the knuckle and then using this completed shape, make a full template out of plywood.  The knuckle template will naturally be separate from the lower part, but when making the skirt, it may be an advantage to leave a web of material between the two curve lines on each side to

facilitate stitching.

If you use straight fingers on the bow, you will need to make approximately three fingers on each side with progressively more knuckle bellow to accommodate the transition between the straight fingers and the extended fingers.

THE BAG AND FINGER SKIRTThe integrated bag and finger skirt compromises between the flexibility of the finger skirt and the economy of the bag skirt. It is the most complex and sophisticated Hovercraft skirt - a combination of a pressurized bag skirt and  finger skirt. This combination uses the positive aspects of both skirt designs while only implementing marginal disadvantages of the finger and bag skirt. You will see this skirt design in nearly all commercial craft and some noncommercial.

Detail of commercial Bag and finger skirt as used on the Hover ferry.The advantages are a relative smooth ride over most uneven surfaces with the finger section quickly adjusting to the surface contours. Low friction from the small cross section of the finger compared to the wide and relatively inflexible bag skirt. As shown in several tests it is seldom that you damage several finger at the same time and it is easier to repair in the field once damage occurs than a bag skirt. Even with the partial loss of up to 3 finger your craft will fly safely. Most of the time you can get your craft at a save location if not even back to your home base or trailer. It is easier and more inexpensive to replace some finger than a whole bag skirt of a craft. All patches and repair on a bag skirt will only be quickly chaffed off if they are close to the "ground contact" line. While a replaced finger has the same ground contact shape as all the other finger and will not be worn off quicker than the surrounding finger.  

Reduce "plow in" compared to a racing finger skirt  provided by the upper bag section of this skirt. The bag section is not only a flexible  attachment for the finger but as well a pressurized flexible cushion to the craft. The bag section provides higher stability to the craft while absorbing great forces to the bow and side section just before "plow in" would occur. In the integrated bag and finger skirt ( short B/F-skirt ) the bag section

can be easily drained once water found its way in. Several small drain holes in the bags aft section will allow the water to drain out of your skirt and hold craft weight low.

Where there is a lot of sunshine is always some shadow - the biggest disadvantages of the B/F-skirt are the high weight, big amounts of material and much labor to build. Because of these downsides this skirt design is not at all useful for a racing craft. A craft mostly used over ice or smooth water would as well not benefit from the B/F-skirt. For all cruising craft with a mixed use of land, water, ice and uneven terrain the skirt would provide the biggest benefit. If you use your craft over not totally frozen bodies of water you could reduce damage from floating ice.  As you see the skirt selection is mostly done from the final application of your craft.

 Building sequence:

You can break down the building sequence into five  major steps : 1.)  Dimension of bag section and finger. 2.)  Cut and mark the fabric for final glue joints 3.)  Glue the finger to the bag sections and bag sections to each other 4.)  Apply to craft and adjust bounce web. 5.)  Set your craft on temporary feet, start lift and mark ground contact line on finger, cut  in shape and enjoy flying.    

 Sequence 1.)

Before you can get your bag and finger cross section you have to determine your actual hover height which should be about 10% of your craft width.  Once you know your hover height the bag section should provide 10 - 20 % and the finger section the remaining 80 - 90% of your final hover height.  Hold in mind that your bag section has to provide a section which is  parallel to the surface  to attach your finger.  Once you have the shape you can either make a temporary  mock up to get the dimensions or follow bag skirt and finger skirt pages for the dimensions.

Bag section moldsSequence 2.)

Take the dimension (length ) from the  lower skirt attachment line and top skirt attachment line  of your craft. Mark and cut the fabric as well as mark the final glue joints. Start with the side sections of the craft , and mark the bag skirt section first, remaining fabric can be used for finger. On the outer surface of the bag skirt panel mark the location of your finger - it is useful to start from the CL of the bag and work yourself to the aft and front corner. Leave the last 1 ? ? ( or 50 cm ) open for the final corner finger  - which can be easiest done if your bag skirt panels ( side and front / aft ) are temporary glued together. Mark the corner glue joints and don't forget to allow at least ??  ( or 1.2 cm ) for overlap and glue joint. Turn the bag skirt fabric around and mark location of the bounce web.  Once you have all lines on the fabric, make a template of a single finger and mark to the left over material. Satisfied with the layout start cutting all the finger and bag skirt sections.

Sequence 3.) 

Lay the bag skirt sections (sides of craft) on a flat surface and make sure that there are no wrinkles in the fabric. Glue every second finger ( reference point A ) to your bag skirt section. Allow enough time for the glue to set before bending them over and glue one side section ( reference point B ) to the bag section. Do not attempt to glue both at the same time since this would loosen the wet glue joint. After the glue has adequate set apply the last finger section ( reference C) to your bag section. 

Top= Finger / X-X-X- Line = folding line top = a, left = B , right = C  Bottom template for finger 

Once  you are done with the first set apply the remaining finger ( every second one) on glue joint (reference A) to the bag section. Allow at least 24 hours for your glue to set before applying the side sections of these finger in the same building sequence as described above for the first set. Before gluing the finger to  the front and aft sections of your skirt verify your CoG on the craft and be sure that the fingers ground contact line  will have an equal distance ( CoG to front ground contact line as well as CoG to aft ground contact line.) to the CoG. Only if this is the case start gluing the finger in the same sequence as on the side panels of the skirt. 

side front and aft finger attached - ready for corner layoutOnce all finger are attached to your bag skirt  section decide on a nice and clean layout for the corner finger. This is best done when you glue the corners of the bag skirt along the lower corner together while the fabric is still laying flat on a surface.  Even if it is very time consuming to apply the corner finger - if you rush now you will increase friction of the craft. Once you have all finger in place you can turn your skirt around and it should stand on all the finger 45 degree pointing upwards. Apply the bounce web to the inner side of the skirt and if you are 100% confident that the dimensions are correct - glue as well to the top craft attachment line (not recommended). Now is the best time to glue all corner joints on your bag section.  More or less done deal.

Sequence 4.)

Once your skirt is all glued and well dried - you can start to attach it to your craft - start with the aft lower craft attachment line and work yourself forward. Once the skirt is attached to the lower hull set your craft on a leveled surface. Now the bag and finger skirt should lay quite flat to the  floor and it is the best possibility to attach the bounce web ( temporary with SS staples ) before you fold the

bag section over and attach to the top hull attachment line. When the skirt is all sealed it's time to start your lift unit and apply pressure to the skirt - the bag section should inflate while the finger should slowly expand and hold the air under your craft. Most of them will be tucked under the craft and show wrinkles in the ground contact line. If you have no major wrinkles in the bag section and the appearance is more or less smooth it's time to get to the final adjustment of the finger.    

Sequence 5.)  

Final adjustment. Try to support your craft  on a leveled surface to actual hover height. The easiest way is to let the lift unit lift your craft and slide precut temporary feet under the craft. Once you have supported your craft even - reduce lift pressure to just over idle. This should provide enough pressure to hold the bag section inflated and apply a small amount of pressure to the finger.  Mark all finger along the ground contact line and shut lift unit down. Once the pressure escaped from your skirt it is relatively easy to cut your finger in shape. Just for safety reasons leave at least ?? (1.2 cm ) from your marked  ground contact line to the actual cut. 

Once all finger are even the required air volume should be less and friction between surface and finger nearly nothing. Start your lift unit and your craft should fly gently off the temporary feet - ready for your first test flight.