A large hovercraft that you can ride! I made this before I found instructables so these pictures are the best I could do.

Step 1: Materials

1. Shopvac.
2. Plywood, 3ft or 4 ft square, 3/8in or 1/2in thick.
3. Coffee can lid or other small plastic disk.
4. Tarp 1ft larger then the wood.
5. Electric saber saw, drill, razor, staple gun, duct tape.

Step 2: Make the Board

Cut the plywood into a circle, or any other shape, with a 4 foot diameter. Cut a hole in the plywood that fits the shop vac hose exactly. It is a good idea to outline the hole by tracing your pencil around the circumference of the hose. If it isn't perfect you can later seal it with duct tape. This hole must be placed half way between the center and the edge of the plywood.

Step 3: Make the Skirt

Lay your plywood in the center of the plastic sheet or tarp. Fold the edges of the sheet up over the plywood, then use the staplegun to staple it to the top of the plywood disk. Put the staples about 4 inches apart around the whole circumference. The plastic should be tight against the wood, but not too tight or it will tear when inflated. Cut off the excess tarp and seal with duct tape.

Step 4: Skirt Underside

Poke a hole in the center of the coffee can lit. Attach it to the bottom of the hovercraft with small skrews. It goes over the plastic sheet and pins it to the wood. This helps with lift.
Cut six vent holes in the tarp with your razor. Make shure to space them so there is plenty of space between each hole. If they are too far away from the center they will be plugged when the sheet lays against the floor.

Step 5: Finished

Flip the hovercraft over so the plastic sheet is on the bottom. Place it on a smooth floor and stick the shopvac hose into the hole. Turn it on and the skirt should inflate. If not lift up the plywood and let it inflate. This hovercraft can easily lift one adult, and has lifted two adults with a lot of strain. The amount of total weight that a hovercraft can raise is equal to cushion pressure multiplied by the area of the hovercraft.