In High school physics, we have a project where in groups of 6 people, we build a boat using whatever we want. We have a month to build a boat that can carry two people and can race against other boats from a different school. Is it better to build a cardboat boat or a plywood boat? Where should we start? Please help and give ideas..plywood the cardboard would absorb the water.

First decide how big to make it. By Archimedes principle, it will have to displace an amount of water equal to the weight of the boat plus the two passengers.

The depth of the boat needs to be less than the depth of the water, of course! sail

You probably need to make a frame, for strength, and then cover it with something waterproof. A box shape (vertical sides and flat bottom) is probably easier than a traditional boat shape with a keel.

You could use (thick) plastic sheet as a covering material instead of plywood.

Think about stability – see the reference. The passengers will probably need to sit or kneel, so you need enough space so they can do that.

To race, the passengers need to be able to row or paddle, and also steer.

More information at How to build a boat carrying two people for physics class?