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Page 8
Connections and Applications:
Modern Tankers and Submarines
In this activity, we saw how ships use the concept of an average density with buoyancy to determine loading capacities and design ships’ interiors. Another area where this is important is with submarines, not just for the design of the interior space and for load capacity, but also with a submarine’s most critical system: its ability to dive underwater.
Submarines have chambers filled with air that can be filled with seawater to increase its weight relative to the buoyant force of the ocean. By controlling the amount of water in the tanks, submariners can control how quickly the submarine submerges,
and how deep it will dive. When the crew needs to surface, it can use pumps to empty the chambers and lower the weight of the sub until the water pushes it toward the surface.
Picture of Submarine Chambers
Pose this question: If a box shape (like in barges) holds weight so well, why do ships and submarines not have more box-like shapes? What shapes do they have?
Resistance
A boat does not just sit in water - it moves through it using engines and turbines. The engines need a certain amount of fuel, depending on the energy required to travel a certain distance. A box shape does not allow water to move around it very easily; it exerts a lot of resistance compared to a smooth, curved shape. This creates a problem because the more resistance the boat has to overcome in order to move, the more work its engines do. This means that the resistance generated by the shape of the boat affects the amount of fuel needed (Think of the aerodynamics of a car. The shape of the car is designed to minimize friction, in this case with the air, to improve fuel economy). If resistance is increased, it will need more fuel to cover the same distance and thus reduce what cargo can be carried. This is why boats use the shapes they do, even if this design limits the available space.
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