Model boat kits are widely available at hobby, craft and toy shops. Many of these are scale models of existing craft such as naval ships, sailing boats or historic ships. These models are intended for display and therefore do not usually float. Use items from around the home to make a model boat that really does float. You can make a raft, sailing boat, tug or paddle boat in one afternoon.
Lay the milk carton down lengthwise on a flat surface. The seam at the top of the milk carton should be sitting vertically. This will be the bow of the boat. Measure 2.5 cm vertically down from the side facing up and draw a line along the side of the carton. Cut along this line all the way around the carton to create the hull of the boat. If desired, additional cuts along the sides can be made to shape the hull to represent the desired boat style.
Paint the soap bar box as desired for decoration. Make a hole large enough to insert the straw in the centre of the widest side of the soapbox. Glue the box into the centre of the boat hull. The side with the hole should be facing up.
Cut a square of paper half the length of the straw and no wider than the boat hull. Decorate the sail as desired with marker pens. Measure 1.25 cm down in the centre along one edge of the paper and cut a slit in the sail. Repeat on the opposite side of the sail. Thread the sail onto the straw so it is positioned toward one end of the straw. Insert the other end of the straw into the hole of the box. Glue the straw in place as necessary.
Measure a string long enough to thread from one end of the boat over the sail and reach the other end of the boat. Add 5 cm to the measurement. Tape one end of the string to the bow of the boat. Pull the string to the top of the straw mast and wrap the string around twice on the straw above the sail. Pull the remainder of the string tight and tape the end to the stern of the boat. Cut off any extra string. The boat is now ready to sail.
The milk carton can be painted before construction with waterproof spray paint if desired. Allow the paint to dry completely before sailing the boat.
Use a plastic milk bottle instead of the carton if you prefer.