This is how the airflow works on a hovercraft.
For the newbie's here is a animation showing it.
Left is a single engine craft, but the principal is the same, flow to the back for thrust and downwards for lift. Right is a double engine setup.
▲ Animation made by Tony Lafata.
There are different ways to attach the skirt to the hull. Most builders just nail or screw them to a wooden attach-strip. I choose to use the Poly-Fastener from:
←Click here to go there and mail Bob.
This is how it works.
There are two sizes, I bought the "800" type. The "900" was not recommended as it is bigger and heavier, more expensive, and wouldn't hold the tarp we are using as good.
It was $ 77.-- for 100' incl. shipping COD, in the east of the USA. (2003)
First the holes
I made a setup on the work bench, with a counter sink drill (sp) so I could drill holes evenly spaced and deep for the head to sink in. If you don't do that, you'll be ruining the strip.
Cutting them to length is something you have to find out for yourself. The screwing on, too!!
I just want you all to know that a 20 minute pre
heated oven at 195°
F (85°
C) will bake your coils perfect in 10 minutes.
Get them out and put them with the open side down, walk over it twice and they
are as straight as if they where made a minute ago. Watch the hands !! Use oven
mittens or similar. No need to say that this should be done after they are cut
to length and gutted (core taken out).
After two hours driving I got my 3M 5200 kit today !!!
I put on the pre drilled strip loosely with a screw every foot and a half, in a
way that there was a 0.4 inch gap between the hull and the strip. This way I
could easily get the3M 5200 kit between the strip and the hull. No mess,
no stress just a lot of work getting in the rest of the screws ( I'll do a ss-screw
every 2"). An extra pair of hands is nice !
NOW THIS IS HOW IT LOOKS AFTER ALL THE ABOVE
STUFF
STARTING THE SKIRT CUTTING
First I cut the roll of material roughly to length and width for the 9 parts I need, otherwise it couldn't be handled in my attic. Next, I made blown up prints from the drawing. From this I could take sizes and calculate the real live sizes. This was drawn on the tarp and a pair of scissors did the rest.
The drawings where printed on a grid of 10 X 10 cm ( about 3" X 3") this made live real easy.
This is the skirt-drawing, I have a lot of drawing to do on the real tarp before I can start cutting the stuff.
What I found out !!
There are some basic rules you have to observe.
1: The skirt material will NEVER stretch. So if all the seams are just a bit closer than the official measurement of the outside upper tack-strip is, you’ll have a real hard time getting it on there; if ever !! So take the size real good. I always had them checked by a helper.
2: Think three dimensional (that’s hard) I mean discuss how you look at the craft (from what side) IE what’s left what’s right AND what’s the inside of the skirt and what’s the outside of the material. This all sounds simple, till you cut your first wrong piece of skirt and you’ll think of this piece of poetry !!!! Use a marker and write on every piece of skirt what’s up, inside and front, and most important what piece it is. Where is it going to sit on the craft??
3: Take your time and space to lay it all out. Make first all parts and arrange them before opening the glue.
4: Make seams so that they overlap smoothly in the way of travel, have the overlap-seam- fingers as much as possible on the inside at all times so they can not catch anything (water, dirt, road) Imagine making side slips too. Mark these areas before you start gluing and dry fit them.
5: The overlap-seam- fingers should be around 1”or 1.5” deep and shaped that they have the most surface covering along the whole length of the seam. Take notice of the extra material you need for the tack-strips on top/outside and bottom/inside. Mark this area with a line so when you attach the skirt you’ll have a reference on how straight you’re going along the tack strip.
6: Prepare yourself for double the time you thought you needed. The drying time of the glue, before you stick them together, has to be observed. If there is a beer around it’s easy forgotten and the seam is not 100% if the glue is too dry.
7: Write the sizes down as you go along the whole procedure; this saves you a ton of work the next time. If possible, make moulds/patterns of the complex corners. Plywood or rest skirt material will do just fine. Don’t forget to mark them ( in, out, up. front etc.) Do this, otherwise they’ll end up as a repair patch or bird feeder next year !
8: Find or make a roller (worst case buy) so you can squeeze the seams real good after you stick them together. Start squeezing ASAP after putting the parts together. It’s no use when the glue is on there long. Doing repairs under the craft, I used a rubber mallet and a block of wood to “hammer” the seams for a good bond.
9: Hang your skirt on the craft loosely when starting attaching. If possible inflate the skirt if it’s on just enough, so you can see if the corners are ok and if the lowest point of the skirt is nice and straight all the way around. Corners tend to drop a bit due to there weight.
10: Scissors work better than knives, and knives make faster and bigger mistakes. One exception for this is making the V-cuts. Draw where the point of the V-cut has to come with your marker (dot just off the actual seam) put the point of the knife on the dot and cut outwards. The V-cuts can be even smaller then in my drawing, for a larger contact area.
Old V-cuts good for straight- not corner seams Let it hang loose and look if all fits well before finishing
Winter 2008-2009
I'm thinking of making fingers under my skirt. After looking at some craft this summer, I'm still doubting, if it's worth the effort.
It's a lot of work and my hull is not 100% build to have a bag/finger skirt. Only luck I have is that my bag pressure was way to high. So I think it could be a good option to save on ware on the bag and have just that 3" more lift hight.
I'll let you know if I start or not!