Sept 16th- GRNG 101- Boat Design Challenge

The Greenengineering 101 students did another introductory design challenge:

Working in teams of 2, design a boat structure that will carry at least 25 pennies, and that will fit within the aquarium.

Available Materials: 

• Large Plastic Cup
• Duct Tape- 12"
• 10 plastic drinking straws
• 10" of plastic wrap
• 1 item from the prototyping bin.

The design above was very stable, as the pennies were below the waterline, lowering the center of gravity....

Straws serve to increase the initial stability of the boat....

Discussion:

Large variety of designs- in engineering, there are often many possible solutions.

Some design solutions tended to converge.

Ship stability - low center of gravity helps ship be more stable

https://en.wikipedia.org/wiki/Ship_stability

The ship is stable because as it begins to heel, one side of the hull begins to rise from the water and the other side begins to submerge. This causes the center of buoyancy to shift toward the side that is lower in the water. The job of the naval architect is to make sure that the center of buoyancy shifts outboard of the center of gravity as the ship heels. A line drawn from the center of buoyancy in a slightly heeled condition vertically will intersect the centerline at a point called the metacenter. As long as the metacenter is further above the keel than the center of gravity, the ship is stable in an upright condition.

Video:

Discussion: The Swedish ship Vasa  sank a few minutes into its maiden voyage due to an excessively high center of gravity:



https://en.wikipedia.org/wiki/Vasa_(ship)

"...Vasa sank because it had very little initial stability, which can be thought of as resistance to heeling over under the force of wind or waves acting on the hull. The reason for this is that the distribution of mass in the hull structure and the ballast, guns, provisions, and other objects loaded on board puts too much weight too high in the ship. 

The center of gravity is too high, and so it takes very little force to make the ship heel over, and there is not enough righting moment, force trying to make the ship return to an upright position. The reason that the ship has such a high center of gravity is not due to the guns. These weighed little over 60 tons, or about 5% of the total displacement of the loaded ship. This is relatively low weight and should be bearable in a ship this size. 

The problem is in the hull construction itself. The part of the hull above the waterline is too high and too heavily built in relation to the amount of hull in the water. .."