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Floating Ships and Boats Lesson

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I am a Christian. I was an 8th-grade American History teacher. I am currently a freelance writer, public speaker, & homeschooling mom of 9.

A sailboat

A sailboat

This is part 2 of a 5 part hands-on unit study on Floating & Flying (Fluid Mechanics). This week's focus is ships and boats. Create working models of sailboats, submarines, and hovercrafts, test out jet power, examine the impact of density of liquids and surface tension on floating, and more! My lessons are geared toward 4th-5th grade level children and their siblings. These are lessons I created to do with a weekly homeschool co-op. We meet each week for 2 1/2 hours and have 33 children between the ages of 1-13. Use these fun lessons with your classroom, family, after school program, camp, or co-op!

Please DO NOT copy this elsewhere without giving proper credit: .

(Some photos on this page were taken by one of the mothers in our co-op

who operates Michelle Harrison Photography.)

Devotional: What Does Your Tongue and a Rudder Have in Common?

1. Pray. Read & discuss James 3:3-9. Say something such as:

-What part of the body was this passage from the Bible about? (tongue)

-In this passage, when they talk about our tongues, they really mean the words that we speak. What can we do with our tongues? (bless and curse)

-What did it compare our tongues to? (bridle on horse, rudder on ship, spark, fire)

-Is our tongue a small part of my body? (Yes) Is it a powerful part of my body? (Yes)

-Can we control our tongues, or what we say, or do our tongues, or what we say, control us? (Our tongues control us.)

-We’re going to learn about ships today. From small speedboats to big boats, many of them have a small handle that moves the rudder. The rudder is small in comparison to the entire size of the ship, but if you turn the rudder one way, your entire boat or ship will turn to the left. If you turn the small rudder the other way, your entire boat or ship will turn to the right.

-Can we control our tongues? (No) According to the passage, we can’t. It’s like this fire. [Set a small piece of paper on fire and let it burn up the paper.] I can’t control this fire, and I can’t control my tongue. What did the fire do to the paper? (It destroyed it.) When we use our words to tear others down, we do the same thing to them that the fire did to the paper.

-What can be done about this? [Take out a second sheet of paper that has had half of it soaked in water, and set the part on fire that wasn’t soaked in water on fire.] Just like the water on this paper will stop the fire from burning it up, God can give us the power we need to stop our tongues from saying words that hurt others and tear them down. Instead , He can help us to use our tongues for good, for blessing and encouraging others.

YOU WILL NEED: 2 small pieces of paper, matches or lighter, & tongs (optional)

Density of liquids

Density of liquids

Density of Liquids

2. Review what we learned last week about the definition of buoyancy and what makes ships float or sink.

3. (Prep: Fill 8 clear cups less than ¼ full of water.) Density of liquids: Ask children to remind you of what density is. Some liquids are less dense than water, so they float on top of water. Other liquids are denser than water, so water floats on top of them.

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-Divide children into 8 groups of three. Give each group a clear cup filled less than ¼ way with water. Tell the children the liquid in the cup is water.

-Pass around a bottle of cooking oil and have child #1 in each group pour about a 1/2 inch layer of oil over the water. After everyone has done this, ask them if cooking oil is more or less dense than water.

-Pass around a bottle of pancake syrup and have child #2 in each group squirt some into their cup of water until it’s about 3/4 inch thick. After everyone has done this, ask them if pancake syrup is more or less dense than water.

-Pass around a bottle of dishwashing soap and have child #3 in each group squirt some into their cup of water until it’s about 1/2 inch thick. After everyone has done this, ask them if dishwashing soap is more or less dense than water.

-Ask the children to tell you what they observe. (The layers float on top of one another without mixing. The syrup is at the bottom because it is the densest. The oil is the least dense of all 3 so it floats on the very top.)

YOU WILL NEED: 8 large clear disposable cups, 1-2 bottles of dish washing liquid, 1-2 bottles of pancake syrup, & 1-2 bottles of cooking oil


Buoyancy in Liquids

4. (Prep: Pass out a ball, piece of crayon, piece of uncooked pasta, screw/nail/washer, small twig, and paper clip to each group.)

Ask children what happened last week when we dropped golf balls in the water. Were they buoyant? (No, they sank.)

-Ask the children to make a hypothesis regarding what will happen when they drop the same balls in the cup of liquids.

-Have child #1 in each group hold the ball. Let them drop it in. Ask them, “What happened? Was your hypothesis correct?”(The ball will float on the syrup.)

-Have child #2 in each group pick up the piece of crayon. Ask children to make a hypothesis on what will happen. Let them drop it in. Was their hypothesis correct?

-Have child #3 in each group pick up the piece of uncooked pasta. Ask children to make a hypothesis on what will happen. Let them drop it in. Was their hypothesis correct?

-Have child #1 in each group pick up the screw/washer/nail. Ask children to make a hypothesis on what will happen. Let them drop it in. Was their hypothesis correct?

-Have child #2 in each group pick up the small twig. Ask children to make a hypothesis on what will happen. Let them drop it in. Was their hypothesis correct?

-Have child #3 in each group pick up the paper clip. Ask children to make a hypothesis on what will happen. Let them drop it in. Was their hypothesis correct?

-Ask, “What does this teach you about the relationship between densities of liquids and the buoyancy of objects?

YOU WILL NEED: 8 small balls (like golf balls), 8 pieces of crayon, 8 pieces of uncooked pasta, 8 screws/nails/washers/bolts, 8 small twigs, and 8 paper clips



5. (Prep: Fill 8 cups with very cold, icy water. Fill 8 cups with hot water. Write an “S” on 8 cups. Fill them with the warm water and then pour A LOT of salt into each one. Stir them to try to dissolve the salt into the water.)

We have seen that different liquids have different densities. The denser or “heavier” the liquid, the better is it at making things float in it.

-Give each group 1 of each of the cups (cold, warm, and warm with salt), 3 straw pieces, and 3 small balls of clay.

-Have each child attach a ball of clay to the bottom of a straw. Tell them that this straw is a hydrometer. Have them say, “hydrometer.” A hydrometer can be used to determine the density of water. Hydrometers were invented by Leonardo da Vinci, who was a scientist, inventor, and artist. He painted the Mona Lisa and The Last Supper.

-Ask the children to touch each cup of water and guess what it is inside. Tell them that one has cold water, one has warm water, and one has salty water like what you’d find in the ocean. Ask them to make a hypothesis: Will their hydrometers all float at the same levels in each of the cups of water? If not, which cup will it float the highest in? Which cup will it sink the lowest in?

-Have the children place the hydrometers into the liquids and compare the different levels at which the hydrometers float. Ask the children to tell you what they observe.

-Explain that the particles of dense liquids are bigger or closer together. Dense liquids push harder on the hydrometer. The harder the push, the higher up in the liquid the hydrometer floats. Like air, water expands as it gets warmer and as a result becomes less dense. Water is most dense at temperatures near freezing. When water freezes, however, it expands, becoming less dense. If equal volumes of cold water and hot water are compared, cold water weighs more than hot water. Ocean water has salt, a type of “stuff,” dissolved in the water. With more stuff in it, ocean water is denser than fresh water. Put another way, a gallon of salt water weighs more than a gallon of fresh water. Because of this weight difference, when an object floats in salt water, a smaller volume of water needs to be displaced than would be needed if the water contained no salt. Because less salt water needs to be displaced, an object floats higher in the salt water.

YOU WILL NEED: 24 large, clear disposable cups, container of salt, spoon, 12 straws cut into 2 equal pieces, ice (brought from home), & 24 pea-sized balls of clay


Plimsoll Lines

6. Ask children, “Using what you just learned about the density of salt water and fresh water and hot and cold water, how might that affect how much cargo you would place on a ship? Would that affect how much cargo you would load on a barge that starts out in the fresh water of the Mississippi River but is sailing out to the salt water of the Gulf of Mexico? What about a ship that is sailing from the warm waters of Miami up to the cold waters of Canada?”

-Show children a picture of Plimsoll lines that are painted on the hulls of ships. Have them say, “Plimsoll lines.”

-Ask them what they think they might be or mean.

-Plimsoll lines indicate how fully ships can be safely loaded under a variety of water and climate conditions. These markings came about over a hundred years ago, at a time when England was enjoying the fruits of the Industrial Revolution. Manufactured goods were being produced and exported as never before, and unfortunately, it was not uncommon for greedy ship owners to both overload and heavily insure their boats before launching them on their trade routes. As a result, a great many ships sank in the ocean and were lost; in one year alone 411 ships were wrecked along England’s coast, and over 500 sailors drowned. Not surprisingly, sailors in the Merchant Navy grew reluctant to work on what they considered dangerous ships. Many were more willing to spend twelve weeks in prison for disobeying orders than they were to set sail on such vessels. At one time a prison inspector in southwest England found that nine out of twelve inmates were sailors who had been jailed for desertion. Samuel Plimsoll, a Member of Parliament, became concerned about what he called the “coffin ships” of the times, and fought for several years for safety regulations. In 1876 Parliament pass a law requiring all ships to have load lines painted on the sides of ships. The overloading of ships was not as common in the U.S., and it wasn’t until 1929 that Congress passed the Load Line Act here. Since then, the practice of applying load markings has become worldwide. The basic load line symbol consists of a circle with a horizontal line passing through the center. The letters on either side of the circle indicate the organization that certified the load level. In the example above, the A and B stand for the American Bureau of Shipping. The placement of the line depends on a lot of factors, including various aspects of the hull shape, the length of the boat, and the type of cargo. The additional lines to the right of the circular symbol show the limits for different water types and climates, reflecting the density differences present at the time of loading.

YOU WILL NEED: picture of Plimsoll lines (You can use the picture from or from any other book or website)


Sailboat Models & Rudders

7. You may have noticed that ships and large boats have steering wheels. Smaller boats might just have a tiller instead. Both wheel and tiller are used to control a rudder. The rudder is used to steer the boat. At sea, sailors say “port” for left and “starboard” for right. Ask, “What do they say for right? What do they say for left?”

-We’re going to make a boat with a rudder that you can control. Explain how the rudder works: If the rudder points in line with the flow of water, the boat moves straight on. If the rudder points to the left or right, the flow of water is slowed by it and so the boat changes direction.

-Have children get their Styrofoam tray, scissors, paper, square of plastic, and markers. They can cut out a boat shape from the Styrofoam tray. Tell them the trays will be the main part of their boat, which is called a hull. (Have the children repeat the word, "hull.")

-Tell them that sailboats usually have 2 sails. The big sail is the mainsail. The small sail is the jib. Both sails are attached to the mast using rope. (Have them repeat the words mainsail, jib, and mast after you say those words.) Show the shape of a right angle, and tell them that right triangles tend to be the favored design for sails.

-Let them cut out a triangle-shaped sail out of the sheet of paper. Give the children a couple minutes to decorate their sails using markers. They can make 1 or 2 sails. (*If your children would like for their sails to be a bit more permanent, they can instead make them out of duct tape or cover their paper sails with clear packaging tape.)

-While children color their sails, do the following:

-Give each child a shish kabob skewer and have them push the skewer through the sail towards the bottom and top. If they made a mainsail and a jib, have them put the mainsail on first, pull the bottom part of the sail off the stick, thread the jib on, and then put the bottom part of the mainsail back on.

-Have them use the skewer to push a hole into the bottom of the Styrofoam hull towards the front of the ship. This will be the mast.

-Pass out small balls of clay and have the children place a small piece of clay on the bottom of the skewer (under the Styrofoam) so that it will stay.

-Have the children tape their rudder (a square cut from an OJ/milk container) to a drinking straw.

-Have the children use the straw to push a hole in the hull towards the back of the boat.

-Pass out a toothpick to each child and have them use the sharp side to push through the straw above the boat level. This will be the tiller.

-As children finish their sailboats, let them go outside to launch their boats into buckets of water. They can blow into their sails and steer by turning the rudder. Remind them that “port” means left and “starboard” means right. After the children have had a chance to sail their boats, ask them if they can adjust their rudders so that their boats sail around in a circle when they blow on their sails.

-Have them remove their sailboats from the water and come back inside.

YOU WILL NEED: 48 wood shish-kabob skewers (half will be used for another activity), 24 toothpicks, waterproof tape like duct tape, 8 straws (cut each one into 3 equal pieces), Styrofoam trays or the lids of egg cartons, scissors, markers, paper, rudders (made from a 1x1inch square of OJ or milk carton), pea-sized balls of clay, & containers of water

The physics of sailing


Jet Power

***If you have 16 or more children, divide them into 2 groups and have them rotate between activities 8a and 9a-c. Only include activities 8b-c and 9d if you are not limited by time.***

8a. Most boats and ships have propellers which push them along. The propeller cuts through the water, pushing it back behind the vessel. This push against the water propels or makes the vessel move forward. A jet-propelled boat can travel at high speeds with a propeller. The jet, or fast-moving flow of water, pushes the boat along. We are now going to create jet-powered boats.

-Have children get their soda/water bottles with the hole in them and a handful of pebbles. They should drop the pebbles into their bottles to weigh them down.

-Help them to put clay around the bottle neck to weigh down that part of the bottle.

-Allow children to use sharpie markers to draw designs on their jet-powered boats while you work with individual children to fill up their boats.

-Take the child to the kitchen. Give the child a balloon. Let them stretch it a bit. Tell them to not drop the balloon into the bottle. Work with them to place the balloon inside the bottle with the mouth of the balloon sticking out. Help them to stretch the balloon neck over the faucet tap and fill the balloon half full with water. Have them pinch the balloon neck closed.

-Take them back outside. While they are still holding the end of the balloon, have them pull the balloon out of the neck of the bottle as much as possible (so it doesn't just release inside the bottle). Have them put the bottle in the tub of water and then let go of the balloon. They can watch the jet of water shoot out and push the boat along. (Have them do this as soon as they are ready. Don’t have children wait around and then do it at the same time.)

-Explain that when the water shoots out of the balloon, it pushes against the water in the tub. This pushing force propels the jet boat forward. The quicker the water escapes from the balloon, the faster the boat travels.

YOU WILL NEED: 25 balloons (not inflated), plastic soda/water bottles each with a hole drilled or punched toward the bottom, small handful of peddles or pennies that will fit through the hole in the mouth of the bottle, ball of clay, sharpie markers, & tubs for water


Surface Tension

8b. (Optional) If you are not limited by time, allow the children who have finished with their jet powered boats experiment with surface tension.

-Ask, "Have you ever notices how water collects into tiny drops on shiny shoes?" The weight of the water tries to make it flow and spread but water has a kind of stretchy elastic skin that holds it together. Give each child a cup. Have them pass around pitchers of water. Let each child fill a glass to the top with water. (Please assist younger children.) Ask, "Can you see how the water's surface bulges slightly over the brim of the glass?" The force holding the water together is called surface tension. Have the children say, "surface tension." Pass out a small sheet of tissue paper and a sewing needle to each child. Do they think it will float or sink? Normally it would sink. Demonstrate this, but tell them to not do it themselves. A metal needle does have a higher density than water, so it should sink. However, sometimes the water's surface tension can help out the buoyancy of an object. Have the children float the needle on the "raft" of tissue paper in their cups. The tissue paper will become waterlogged and will sink, leaving the needle floating in the water.

YOU WILL NEED: cups, pitchers of water, tissue paper, sewing needles


8c. (Optional) If you are not limited by time, pass out a piece of cardboard to each of the children. Have them use scissors to cut it into a boat shape. Let children use pens so to put their names and a design on their boat. While they are doing that, use a nail to punch a hole near the stern (middle back) of the boat. Have them cut from the stern of the boat to the hole. Have them put the boat into a small container of water and watch their boat float. Quickly squirt liquid soap or glue into the hole near the stern. The boat will shoot forward. Ask the children why they think that happened. Explain that the soap breaks up the surface tension in the water behind the boat. The surface tension pulls the boat forward. As the soap/glue wakens the surface tension at the back of the boat, the boat floats forward, pulled by the stronger surface tension in front. Some pond insects can skim along the surface of the water in the same way. They're light enough that surface tension can hold them up, and they use their legs to break up the surface tension just enough to move.

YOU WILL NEED: cardboard (2x4 inches), scissors, pens, liquid soap, containers for water


9a. Ask children if they can name any famous ships. Tell them that we’re going to read about the largest passenger steamship ever made at that time in 1912, almost 100 years ago. This “unsinkable” ship sank on its first voyage across the Atlantic Ocean. Read a book about the Titanic, Survivors the Night the Titanic Sank by Caryn Jenner.

YOU WILL NEED: Survivors the Night the Titanic Sank by Caryn Jenner


9b. Ask the children from what they know about what floats and sinks, why did the Titanic sink?

-Show the children an ice cube tray. The Titanic had 16 huge compartments of air, called bulkheads. (Have the children repeat, “bulkheads.”) The compartments of the ice cube tray represent the individual bulkheads of the Titanic.

-[Place the army men on top of the ice cube tray.] I’m adding the toy people to remind you that there were over 2,000 people (dads, moms, brothers, and sisters) on the Titanic.

-After the ship hit the iceberg, the compartments of air (Ask, “Which are called what? bulkheads) began to fill with water. [Fill the first two compartments at the end of the ice cube tray with water – as if water is entering the hole in the side of the Titanic.] What happens? (Not a lot). [Tip the ice cube tray to the right so water leaks into some of the compartments and spills over the lips of the ice cube compartments until all the compartments on the right hand side and fills them] What happens.? (The tray starts to tilt at that end where the water has displaced the air. The water leaks over into the other compartments.)

-[Allow water to fill it the tray completely and then push the tray under the water – as most ice cube trays will float in water even if they are full.] lAs the water flows filling the compartments, the tray/Titanic sinks. The sinking of the Titanic is a great example of what happens when the air is forced out of a steel ship. The Titanic was designed to be unsinkable. It was made of steel and was watertight. Therefore, no water could get in from the outside. The problem was that the compartments inside the vessel were not “watertight”. Each compartment did not extend right to the top of the hull – effectively allowing air to flow from one compartment to another. When the iceberg ripped a horizontal hole in the side of the ship, the compartments started to fill with water. As five of the compartments filled with water, enough air was pushed out of the ship to lower the front end (the bow) deep into the sea. Water continued to pour over the top of the breached compartments into those that were still full of air. The more the Titanic sank, the more water poured into the air- filled compartments and the heavier the vessel became. Eventually, air was forced out of the hull so that the whole ship became heavier than the water around it and consequently the Titanic sank, along with about 2/3 of the passengers and crew.

YOU WILL NEED: 1 ice cube tray, some army men or other toy people who can get wet, 1 plastic container (like a plastic shoe box – it needs to be large enough to hold the ice cube tray) filled with ice water, & 2 towels


9c. (Prep: Ahead of time, fill your 2 bowls with ice and water and put them in the freezer. You’ll want them to be as cold as possible.) Many people died of hypothermia. The Atlantic Ocean water was so cold that it froze the people to death. The water was 28 °F/-2°C. Divide children into 2 groups. Have them place a hand in one of the bowls of ice water. See who can keep it in there the longest. The people left in the ocean didn’t just have a finger in the water. Their entire body was in the water for over an hour before ships came to try to rescue them. It was a very unfortunate event.
YOU WILL NEED: 2 big bowls, ice, & item used above: 2 towels

Titanic trailer

Exploring the Titanic on the ocean floor


Types of Ships

9d. (Optional) If you are not limited by time, ask children what type of ship the Titanic was. (An ocean liner.) Have them name a few other types of ships/boats. Read part of a book about parts of a boat and types of boats, What Makes It Go? What Makes It Work? What Makes It Fly? What Makes It Float? by Joe Kaufman.

YOU WILL NEED: a book about parts of a boat and types of boats such as "What Makes It Go? What Makes It Work? What Makes It Fly? What Makes It Float?" by Joe Kaufman

Good Picture Books on Types of Ships

Also look for "Boats" by Ruth Lachman, "Boats" by Gallimard Jeunesse, "Snoopy's Facts & Fun Book about Boats" by Charles M. Schulz, and "The Big Golden Book of Boats and Ships" by Patricia Relf, and "The Boat Book" by Joe Kaufman. All of these books are colorful and simple enough for young listeners.