Title: Alvin Buoyancy Category: Technology Subcategory: Difficulty: Unknown Year 2004 Bowl: Shore Bowl Author: C. Grant Law Contact info: ext 310 IMCS, Rutgers University 71 Dudley Rd. New Brunswick, NJ 08901

QUESTION Round:Time: 4 minutesStandard/Category: Technology Difficulty: Difficult QUESTION: One of the most significant daily operating costs of DSV Alvin is the iron plates used as ballast on descent. Once Alvin reaches its target depth, the iron ballast is released and abandoned on the seafloor. If the use of disposable iron plates for ballast is so expensive, why is this method preferred? Why doesn’t Alvin simply use its ballast tanks and compressed gas to control buoyancy as military submarines do? Come up with 3 reasons why the Alvin team continues to throw their money away (6 points for each acceptable answer, with a 2 point bonus for answering all 3 correctly).

ANSWER Round:Time: 4 minutesStandard/Category: Technology Difficulty: Difficult QUESTION/ANSWERS: If the use of disposable iron plates for ballast is so expensive, why is this method preferred? Why doesn’t Alvin simply use its ballast tanks and compressed gas to control buoyancy as military submarines do? Come up with 3 reasons why the Alvin team continues to throw their money away (6 points for each acceptable answer, a 2 point bonus will be given if all 3 answers are correct). ANSWER:- Conservation of oxygen and electricity: because oxygen and electricity are being consumed during descent, it is important to get to the work site as quickly as possible. For this reason, the submersible needs to be very negatively buoyant. The massive iron plates accomplish this without being bulky. (6 points) - Quick transition from negative to neutral buoyancy: once the submersible approaches its target depth, it must quickly attain neutral buoyancy by lowering its density. This is easily accomplished by dropping the iron plates. (6 points) - Conserve ballast system’s compressed gas: If the submersible were to use its ballast tanks alone to achieve neutral buoyancy at depth, a volume of seawater equal in mass to that of the iron plates would have to be displaced. At Alvin’s working depths, this could consume a significant amount of compressed gas. (6 points) - Safety: becoming too negatively buoyant as a result of ballast system failures can be extremely dangerous, so the buoyancy of the sub must be very close to neutral when the ballast tanks are full. Without negative buoyancy however, descents are prohibitively slow. The use of disposable Iron ballast allows Alvin to make quick descents without sacrificing safety. (6 points) - Because they can: military submarines must be self sufficient, but Alvin gets re-supplied after every dive. (6 points) If the students include more than one of the above points in a single answer, award 6 points for each. Photograph of ballast plates being mounted on Alvin provided by the author.