With properties of matter in mind, students with visual impairments will design a boat that will hold as much weight as possible.
Possible solutions to a problem are limited by available materials and resources (constraints).
At whatever stage, communicating with peers about proposed solutions is an important part of the design process, and shared ideas can lead to improved designs. Tests are often designed to identify failure points or difficulties, which suggest the elements of the design that need to be improved. Different solutions need to be tested in order to determine which of them best solves the problem, given the criteria and the constraints.

Students may need to practice a variety of shapes and methods to develop the most efficient design. The success of a designed solution is determined by considering the desired features of a solution (criteria). Testing a solution involves investigating how well it performs under a range of likely conditions. Density is a physical property, which means it is same for one substance, no matter how much of a substance is measured.
Different proposals for solutions can be compared on the basis of how well each one meets the specified criteria for success or how well each takes the constraints into account.

Fresh water always has a density of 1g per cubic centimeter; a cup of water in your hand and water from an entire river has same density. If a person goes up to the top of the mountain, his weight will be less, because the pull of gravity on him is less. Therefore, a ship has a much lower density than a solid piece of metal the size of the ship.