Turn the hovercraft hull upside down. Using a pencil, draw two lines parallel to the sides of the hull. They should be offset from the edges by 30% of the hull's width.

With a protractor, draw the bisectors of all the hull's angles. As shown in the picture, use these bisectors to reproduce the shape of the hull at a smaller scale.

You can now cut the two strips and fold them at the correct points to match the lines you previously drew. For small models (up to 40 cm hull width), the height of these strips can be 10% of the hull width. For larger models, I suggest limiting this height to a maximum of 4 cm. You'll notice that the strip isn't perfectly straight, and that there should be two strips facing each other - for me, this hull was just a draft.

Note that the front and rear of the vented bag skirt must remain open to allow air to escape (check this page for more details). This is why skirt attachments are not needed at the front or rear.

You now need to draw the shape of your skirt using drawing software like GeoGebra or graph paper. Draw it at a 1:1 scale to avoid mistakes — you need to be as precise as possible to get a good result. Start by drawing a horizontal line that represents your hovercraft hull.

Then, draw a vertical segment to represent one of your attachment strips (3 cm high in my case, because my hull is 30 cm wide). Next, draw a semicircle, with its center placed exactly below the edge of the hull and facing the end of the attachment strip.

Join the end of the semicircle to the end of the attachment strip with an arc (which is blue, in my example).

Sorry to say that I have no specific instructions for positioning the compass or setting its spacing — I usually try several times until I get a satisfying arc. In this case, the compass was positioned at the top of the drawing, right above the center of the semicircle.

In the end, you get a vertical cross-section of your skirt: this is what your skirt will look like when inflated.

From this single shape, you can design all the corner templates you need, so make sure to save or copy it. Remember that you will need one template for each angle value on your hull.

Erase the hull but keep the attachment strip.

Draw two horizontal and vertical axes that go through the center of the previously drawn semicircle.

Divide the semi-circle into 8 equal circular sectors, each one being 22.5°.

With a compass, measure the length of the arc marked in red. Use this arc length to divide the rest of the skirt. If necessary, add a final dot manually at the very end of the skirt, like I did.

On a real hovercraft, where the semi-circle may be around 40 cm in diameter, you can go up to 12 equal circular sectors for more precision — in that case, you will get 15° sectors. Of course, this level of precision is not required for models.

In any case, it is important to divide the semi-circle with an even number to ensure correct positioning of your dots.

I will rotate the skirt 90° to the right to continue the process. Draw three horizontal lines as shown, and a vertical axis.

In this example, let's say I'm making a template for the rear of the hovercraft, where I have right angles (90°). Whatever the angle value on your hull, divide it by two and use that result to draw the diagonal as shown.

Note that the diagonal must not come too close to your semi-circle — adjust your vertical axis accordingly.

We will continue the tutorial with older drawings. Draw a corner like shown.

We begin by drawing the first mark: draw a horizontal line joining the beginning of the skirt to the previously drawn diagonal, and from there, draw a right angle to join the corner's horizontal line.

Draw a horizontal line above the last dot that was drawn and repeat the process to get your second mark.

The space between two lines, noted X on the drawing, is calculated from the following formula: θ × (π/180) × r.

In this example, θ = 22.5 because we divided the semi-circle into 8 equal sectors, and r = 3 because the semi-circle radius is 3 cm.

Therefore, I get: 22.5 × (π/180) × 3 = 1.2 cm.

Once your mark is drawn, erase the two lines that you used to place it, to make your work easier.

Repeat this process for each mark.

Pay close attention to the final dot, especially if you added it manually in the previous steps — in that case, the last two lines at the top of your drawing may not have the same "X" spacing as the others.

To find the final "X" gap, use your compass to measure the distance between the second-to-last and the last dot on the skirt profile (bottom left), and use that value. A very small margin of error here is perfectly acceptable and will have no negative impact.

Connect the dots, and voilà — your template is ready to be transferred onto a piece of cardboard.

As mentioned earlier, you'll need one template for each unique angle on your hull, so repeat this process until you've created all the necessary templates.

You can see here the final result: two 45° corner sections placed side by side. Once joined together — by soldering or sewing — this part of the skirt will form a 90° angle.

Now that you have all your templates, it's time to cut the skirt pieces to the correct dimensions.

Let's say you've made the template for the rear of an RC hovercraft with a 25 cm wide hull. This means the top edge of the skirt piece should also be 25 cm long (or 25.1 cm to leave a margin for sewing or soldering the pieces together).

Thanks to the template, you don't need to worry about the bottom length or the height of the piece — they'll be exactly what you need.

Repeat this process for all sides of your hull.

Just be sure to use the correct templates for each distinct angle on your hull, and to apply the length corresponding to each hull side. If your hull design is complex, a single skirt piece may incorporate two different angle values, as illustrated in the drawing. In that case, you will need to use two separate templates for the right and left edges of those skirt pieces.

The drawing depicts an RC hovercraft hull with its two attachment strips and all skirt pieces ready for assembly. As you might expect, the longer skirt sections are adhered along the edges of the hull, while the shorter skirt sections are attached to the attachment strips—except at the front and rear, which do not have attachment strips, as explained earlier.

I will demonstrate the following steps using an RC hovercraft skirt made from trash bags. Unfortunately, I don’t have any photos of sewing larger hovercraft skirts at the moment, but the principle is exactly the same.

From this point, we need to join the skirt pieces together, either by sewing or by welding. Take two skirt pieces and place one on top of the other, aligning the corners precisely.

Next, take the appropriate cardboard template and position it 1 mm before the corner. Using your soldering gun, slowly trace the shape of the cardboard. The two skirt pieces will melt and fuse together.