How much weight can different types of boat hulls hold?

We built 4 diffrent boat hulls and tested which one could hold the most weight.
Aaron Yeung Sam Crockett
Grade 6


Our hypothesis is: If the boat has a circular hull (Boat 2) then it will hold more weight because the hull will cut through the water instead of tipping the boat over.



 To find our topic, we went to the science buddies website. There we saw the "how much weight can a boat float" project and we thought that it would be fun to build the boats and float them.
What determines whether an object floats or sinks? It is the density of the object compared to the density of the liquid. If the object is more dense than the fluid, it will sink. If the object is less dense than the fluid, it will float. If the object has the same density as the fluid it will neither sink nor float. If too much cargo or weight is added to the ship, the density of the ship becomes greater than the density of water, and the ship sinks.
 Background research for a flat bottom hull: in this case the flat hull is designed to rise up and ride on top of the water rather than cutting through the water, thereby encountering the reduced friction of moving through air instead of water. Boats with "flat-bottomed" hulls are very stable, great for fishing and other uses on calm, small bodies of water.
 Background research for a round bottom hull. Round-bottomed hulls are typically displacement hulls, and are designed to move smoothly through the water with little effort. An example of a round-bottomed hull is that found on a canoe. One drawback to the round-bottomed design is that it’s less stable in the water and can capsize more easily. So, extra care needs to be taken when entering, exiting and loading these types of boats.
 Background research for a V shaped hull. V-shaped hulls are planing hulls, and are the most common type of hull for powerboats. Deep v-shaped boats are designed to plane on top of the water at higher speeds and provide a smoother ride through choppy water. These boats are usually equipped with a larger engine than flat or round-bottomed boats.
 Background research for pontoon boats. Pontoon boats have a flat-bottomed hull that relies on long cylindrical tubes, called pontoons, for buoyancy. Pontoon boats float, with their pontoons, due to the principle of flotation that states when a boat displaces an amount of weight in water that is equal to its own weight then the boat will float. Multi hull boats are some of the most stable on the water.



Our controlled variables are: Amount of cardboard, Water temperature, Type of  weights, Type of tape, Type of scale and Where we put the boat in the hot tub. 

Our manipulated variables are: The shape of the boat hull and The amount of tape used.

Our responding variables are: The amount of weight the boat was carrying when it sank.




  1. Use the cardboard and tape to construct at least four boat hulls with different sizes and shapes.
    1. You can fold or even cut the cardboard if you want.
    2. Make sure the hulls are not too large to fit in the Hot tub you will be using.
    3. Make finishing touches to the boat hulls so that they are ready to test.
    4. Make sure the hulls seem to hold their shape. If they do not, add a little tape to make them stronger.
    5. Assign a number (1 to 4) to each boat hull. You could do this by using a permanent marker to label each hull with a number or by putting a flag on the boat to identify each boat hull. You can also draw or discribe each boat like we did. However you do it, just be sure you have a way to identify each hull.
    6. Get the boats ready for testing.
  2. To mesure the volume of each boat we used a displacement method. We filled up a bucket of water with markings of the amount of water. Then we submerged the boat enough so most of it is in the water, but no water is leaking in. Then we looked at how much the water went up. Then we had to do lots of calculations on how to get g/cm3. The displacment method eliminaded the whole size varible.
  3. Put a boat in the hot tub.
    1. Keep adding a marble to each side of the boat until it sinks.
    2. When ever you put a marble into the boat, be ready to catch it in the net incase it sinks.
    3. When the boat starts going lopsided, we will catch it in the net.
    4. If the marbles dont sink it, then we put a 3 pound weight on and then added marbles
    5. Then we put all the weights/marbles on the scale to see how much weight the boat was carrying when it sank.
    6. Record the results in your lab book.
  4. Then repeat the step #3 for each boat.   
  5. Put the results from your lab book on a spreadsheet. We used Google Sheets
  6. Look at the results and record what you see.


We observed that the water was seeping through the cracks in the bottom of the boat. We think that the water on the inside of the boat weakened the boat. Also, when we took the boats out of the water, the inside was soaked. For the flat bottom boat, the marbles weren't able to go on the boat evenly because the divider was in the middle and the boat was a different length on each side. For the V-shaped boat, we noticed that the water seeped in where we cut but didn't where we folded. We think this is because the tape isn't as strong as tape and cardboard together. For the pontoon hull, the pontoons were holo and filled with air, so the pontoon boat had more buoyancy. Therefore; holding more weight.

During this project, we had some limitations. Here are a few, covid hit so we couldn't go to each others houses. Sam plays hockey so he can't work sometimes. Aaron sometimes can't work so we can't present or practice on those days.


Boat 1 the flat bottomed boat held 0.301 g/cm3

Boat 2 the round-bottomed boat held 0.770 g/cm3

Boat 3 the V-shaped boat  held 0.435 g/cm3

Boat 4 the pontoon boat held 0.161 g/cm3

We did not do the second test because it takes too long to build the boats and with covid, it's hard to get together and do our testing. In the future, we could make multiple boats instead of only one. Then we could test multiple times at once. This would make out test more acurate.


Our hypothesis was correct. Our hypothesis was right because boat two held the most weight, and when we put another weight on it sank into the water a tiny bit, instead of tipping over.


Our project helps the world because if people want to build a boat then they can look at our project and decide what boat to build. Our project will tell them which type of boat hull is the most sturdy, so, if they want to build a boat with a sturdy hull then they know to build a round bottom boat. 

Sources Of Error

We could have done better in these areas:

- Making sure the boats are the same size. We used the same amount of cradboard to build each boat, however; we did not think about what would happen if we did not use all of the cardboard. For example: Aaron used all of  his cardboard but I did not. Therefore; Aaron had bigger boats than I did. We fixed this by useing the Archimedes method.

- Making sure the amount of tape we used was the same. We did not think about the amount of tape we were useing and how it would affect the amount of weight the boat held. For example: Sam put tape on he inside of the boat so it was better at keeping the water out. However; my boats did not have tape on the inside of the boats so the water weakend the boat from the inside. The water on the inside of the boat also affected the weight of the boat. It made the boat sink faster because the water weighed the boat down.

If we were to do this again, then we would:

- Use the same amount of tape. (example: one roll each boat)

- Plan ahead of time. (example: Plan when we are going to present)

- Talk about how we should build the boats so they are all the same. (example: With or without tape on the inside)


We would like to acknowledge our parents for: Letting use use Sam's hottub, Buying our materials, Helping us measure volume and Helping us edit and present.

We would also like to acknowledge our teachers for: Giving us feedback to make our presentation better, Helping us edit to make our slide show better and Supporting us the whole time.