This is an Instructable on how to make a rubber powered windup power boat. I have seen many wind up airplanes using a propeller. I have seen a lot of variations on paddle boats including one I did for another instructable. Paddle wheels lend themselves to be easily made since the paddle can just be put between a rubber band to make the power plant. I haven't really seen an example of a rubber powered boat propellor so I decided to try making one. I am quite happy with the results. I created the model using AutoDesk Inventor and used the laser cutter at TechShop Detroit to make the parts. Everything else is commonly available at a good hobby store.
I made it at TechShop
Step 1: Create the Propeller
I started with a Brodak 5" diameter propeller I found at the local hobby store. I cut the blades down to 2 inch diameter. Boat propellers are typically very small diameter relative to airplane propellers. Every wind up airplane propeller is setup for rotation as a tractor prop and not a pusher. If you look at the end they are setup so that the wire driving it only can push the propeller one direction. So to get it to function as a pusher propeller which is necessary for a boat requires a little rework. After reducing the diameter you need to cut groove into the hub of the propeller so that the metal wire that drives it can engage going the other direction. This will allow it to function as a pusher.
After doing this I removed the paddle wheel from the paddle boat I made for a prior instructable and glued a stick to it and mounted this propeller to test and see if it works. It worked much better then the original paddle wheel did. Concept works so on to designing the rest of the boat.
Step 2: Design the Boat on Autodesk Inventor
I designed the boat in the form of a Hydroplane. A catamaran with a center mounted, rear driving propeller. This is similar to the form of a racing hydroplane. I guess if you really cranked on the rubber band hard you might get some float going. Maybe. The boat is drawn so that all the parts will fit on a sheet of 1/8" x 3" x 24" balsa. The end of the motor stick needs to be 1/8" x 3/8" for the propeller to stick onto.
Step 3: Laser Cut the Parts
I laser cut the parts on the Epilog 60 watt laser cutter at Tech Shop. The settings I used for 1/8" balsa were 35 speed, 40 power, 500hz frequency. I have gotten good results cutting with these settings.
Step 4: Assemble the Pontoons
First, put the 2 pontoons together. There is a left and right side which are not the same. All the parts are the same but they need to be put together so that the inner and outer sides of the pontoons are on the right sides. I do this by laying down 2 inner hulls facing opposite directions and build onto those. I first glue 2 layers of hull sections onto each one, for lack of better words to call them. Then I glue the hull outer side to each of those. After that I sanded them a bit to smooth up the 4 layer seems. I used CA glue for this. The whole thing can be assembled in a few minutes. The hulls could be painted with epoxy or something else to make them water proof. I did not for this version.
Step 5: Attach the Pontoons and Motor Mount
Next I put the motor mount stick and the 2 pontoons together and then glued together. The hull platform can go on 2 ways along with the motor mount. It should go as pictured with the motor mount being shorter then the rear of the pontoons. This way the prop won't extend out too far beyond the back of the boat.
Step 6: Mount the Propeller and Give It a Try
Slide the propeller onto the motor mount stick. Stick a pin into the front of the motor mount stick to hold the front of the rubber band. I am using 1/16" x 1/8" rubber band that is commonly available at hobby stores. I used about 1 foot of rubber band cut from a 16 foot section. I put the rubber band through the ring on the propeller and tied a knot at the ends. Then I placed that around the pin. Now everything is set to go. Care must be taken when winding this as it's easy to wind it the wrong direction. The only consequence being that your boat will go backwards. This setup seems to work very well and gives good duration and power for the boat. I am quite happy with how it turned out.
Step 7: Video of Boat
Image should be a video file. Hopefully it works.