Our mission was to build a fully operational sub out of some acrylic plastic tubes and a little elbow grease. We decided to salvage the motors and battery from a previous submarine to drive and power our sub. The original designs for our submarine had our sub made up of four tubes, one central tube with the battery with two engine tubes at an angle downwards on the sides and a ballast tube on the top. We eventually discarded this design because of its instability. The ballast system we decided on using consisted of a tube with four bulkheads.  The four bulkheads would stop water from sloshing around inside the tube and destabilizing the submarine. The tube would have numerous holes drilled in it so that it would flood with water. The incoming water would displace the air, reducing the sub’s displacement and causing it to sink. When air was pumped into the tubes, it would force the water out, thus increasing displacement, and causing it to rise. The second design of our sub was similar to the first one but the engine tubes were on the same plane as the battery tube instead of below it. This design would be more stable than the previous design. Eventually, we decided on this design, but not without minor changes. The single ballast tube was cut in half into two tubes and both were raised up above the battery and engine tubes by about an inch and a half. We had to remove the camera because of insulation problems, and the central “arm” of the sub was eliminated because of time and material restrictions.
    Although we managed to get the sub ready in time for the long beach trip, we could not test it because of a lack of time. When we reached long beach, we discovered to our dismay that one of the engines was cavitating. This means that the plane of the propeller (the invisible “wall” that the blades create) was too close to the edge of the tube, so that the water that the propeller had just pushed out would leak backwards behind the propeller, just churning the water, and producing very little, if any, thrust. We fixed this problem by extending the tubes. After this adjustment, the thrust coming from both engines was about the same, ridding our sub from moving in a perpetual turn. Our submarine, while being maneuverable, was slow. Its short length provided its maneuverability, but the tubes themselves were not hydrodynamic, resulting in a lower speed. However, the sub’s overall construction gave it more strength and durability (think short and stout). The aluminum frame that all of the acrylic tubes were attached to, added weight, but also helped reinforce the sub because it reduced the number of holes we needed to drill in the body tubes of the sub. Overall, we were too optimistic about our hypotheses, however, it performed all of the tests well. For the speed trials above the water, we had 14.65% error, which was fairly high, but it can be attributed to our differing piloting skills. Below water we had less error, 4.32%. Our sub’s average left turning radius was about 14 1/3 inches with a 9.3% error. The average right turn radius was 17 inches with an error of 9.8%, which could be attributed to interference (waves, etc.). In our tests on the buoyancy system, going up five feet, our sub had an average of 12.77 seconds with an error of 7.92%. Going up, the submarine had an average of 7.89 seconds with 6.54% error. Despite these high error percentages, we concluded that the project overall, was a huge success.
 
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