Recycled Cork Sail Boats Activity

You might that building a DIY boat would be complicated. But these little recycled cork sailboats make it so easy to put together. They need just 3 used corks and some elastic bands to make a raft that actually floats! Take them out for a sail on the pond or paddling pool on a sunny day. Or you could even try them in the bath. A perfect spring or summer craft for our students.

Our 5th graders tested sailboat sails and designs. The Sailboat STEM activity is a great way to incorporate the engineering design process into the classroom!

Materials

  • Wine corks (3)
  • Rubber bands (2)
  • Toothpick
  • Several screws or nails
  • Craft foam, wax paper, or paper milk carton to make a sail
  • Aluminum foil
  • Sink, bathtub, or a large container you can fill with water. The container should be deeper than the length of your nails/screws.
  • Tap water

Instructions

Step 1: Make your cork raft

Choose three corks and join them together with two elastic bands. If you want your boat to be really secure then you can glue the corks first and then wrap them with elastic bands. Use a strong PVA glue or a glue gun if you’re doing this.

Step 2: Make the sails

Cut two sail shapes out of strong paper or card. Then cut two little diamond shapes out of card/paper too (see step 5). These will be your boats’ sails.

Step 3: Thread the sails onto their poles

Make holes in the sails using a hole punch and pass the straw through. If you’re using skewers then you can just poke the end of a wooden skewer through the top of your sail. Push it through and make another hole at the bottom so that the sail is threaded onto the stick. Take care with the pointy ends of your skewers if you are doing this craft with very small children. You might want to put a ball of plasticine on the top of the pole for added safety.

Step 4: Add your sails

Cut the straws or wooden skewers so they are not too long. Then poke the pointy end of the skewer into the middle cork on your raft. Or if using straws, glue the bottom of the straw in place between the corks.

Step 5: Pop the flags on top

Fold the small diamond that you cut out of paper and glue it to the top of your flagpole to complete your boat. Your cork boats are all ready to set sail.

Digging Deeper

Do you remember playing with toy boats in the bathtub, or have you ever been on a real boat? Boats can float because of buoyancy. While they are pulled down by the force of their own weight (caused by gravity), they are pushed up by the buoyant force, which is equal to the weight of the volume of water that they displace. Some boats are made of materials that are less dense than water, meaning they have less mass per unit volume. These materials (like cork) will always float. However, other boats are made of metals like steel that are much denser than water—so how do they float? They can float because they’re hollow, so there is a bunch of empty air space inside the boat’s hull. The average density of the boat (including both the metal and the air) is lower than the density of water.

But boats don’t just need to float – they also need to stay upright and avoid capsizing (flipping over). To do this, they need a low center of mass, meaning their weight is concentrated towards the bottom of the boat, not the top. That might seem like it’s a problem for sailboats, boats with very tall sails that stick way up into the air. How do they stay balanced with so much mass concentrated way up high? They do so with another part called the keel, which is on the bottom of the boat (so if you’ve only seen a sailboat from above the water, you might not even know the keel exists!). The keel is a big part under the boat, shaped like a fin, that serves two purposes. It holds the ballast, or heavyweight, that helps lower the boat’s center of mass. It also helps prevent the boat from being blown sideways by the wind. In this project, you made a keel from nails and aluminum foil, which helped prevent your sailboat from flipping over and helped it go straight.