Propellers are neat things that you can attach to motors. When they turn, they create a pressure difference on the front/back of the blade. The front has high pressure, and the back has low pressure.
These are done in Sketchup using a technique that I am developing. Each blade is 120 degrees from the others. The profile is extruded up 1/16" and then the top edge is rotated on the center point. The new top edge is then extruded again 1/16" and rotated by the same number of degrees. There is a line through the center to help locate the rotation point. This line would also be useful for placing a hole to accomodate a motor or other post.
This design would be good to print and then make a mold of so you could make lots of propellers for underwater robots or airplanes or similar.
After printing a few versions, it appears that the props need to have a steeper angle for proper Makerbotting. This will reduce the overhang, but will likely also require a taller blade to get enough surface area on the blades.
If the profile of the blade is 1/16th of an inch, it seems to print neater and faster with abs. The included g code is based on MK5 with automated build platform. Having the angle too steep also makes for a sloppy print with lots of loops and drips. The three holes will allow the prop to be bolted onto a laser cut acrylic motor adapter.
Print it out and see how well it works.
You will need to make a center hub for attaching it to the rotational device of your choice.
This is a very new design and technique, so mess with it and share your results!