Building a boat out of straws takes some creativity and design flexibility. Plastic straws are light enough to float on water, making them useful materials for boats. Build every part of the boat out of straws, except for the sail and deck. To have a fighting chance in a boat race, your straw boat should be waterproof and relatively stable.
Form four plastic flexible straws into a square. Bend each straw at its joint. Insert the shorter end of one straw into the longer end of another. Repeat until all four straws are connected into a square.
Spread plastic wrap over the top of the square. Tape around all four sides of the square, sealing the plastic wrap to the straw square with duct tape.
Poke a hole in the plastic wrap with a knife. The hole should be close to the edge on one side of the boat. The hole must be large enough for a straw to fit in it.
Cover one end of another straw with duct tape. The duct tape should be secure so that water can not travel up the straw. Insert the straw into the hole in the plastic wrap so that the duct taped end is underneath the boat. This straw is the mast. Cut a 3-inch piece of duct tape in half, lengthwise and secure the straw to the plastic wrap. Use the other half of the duct tape strip to secure the straw to the plastic wrap on the underside of the boat. If the hole is too big, cover the rest of it with duct tape.
Form a triangle out of 3 straws. Attach them in the same manner as the square. Cut a 6-by-6 inch piece of plastic wrap. Place it over the straw triangle and tape it around the edges of the triangle with duct tape. This is the sail. Tape one edge of the straw triangle to the mast straw with duct tape.
Cover any space between the joints of the straws in the square with duct tape. If there are any gaps, water will seep in and cause the boat to sink.