As I write this, the engine room is carefully adjusting the ship's ballast. This is an interesting physics problem for all you scholars out there. As we burn fuel, we transform the heavy liquid into a gas exhaust that leaves the confines of the ship. Therefore, we're getting lighter.
As we get lighter, we sit higher in the water, losing some stability. How do you correct for that? Can you think of a way to do it? Well, this is actually a topic I overheard Captain George Silva discussing with Chief Engineer Jeff Little and First Engineer Jim Schubert.
If you guessed that the best way to offset the weight of the fuel lost is to replace it with salt water, you're right! Underneath the lowest decks of the ship are the fuel containers and ballast containers. They run all the way from the bow to the stern and all the way from port to starboard. As you may imagine, it pays to have many tanks of different sizes in many locations. But how do you know when to fill certain tanks?
"Well, there's actually a stability program, that takes into account different factors associated with the stability of the ship," said Jim. There are many things to consider, including how far the ship could tip before it would roll over, bow vs. stern trim, port vs. starboard list, and the comfort of passengers (to prevent seasickness).
In addition to all those, this program is designed specifically for Atlantis. It factors in the location and weight of critical equipment such as the cranes, A-frame, and Alvin. That's why it's also important for scientists to provide weights and locations of any significant equipment they add to the ship. As fuel is burned, the computer program factors in all of these issues and decides which ballast tanks to fill.
"Tanks are either completely filled or empty so as to prevent the water from sloshing and upsetting the balance," Jim continued. As we've been traveling and burning fuel, we've been filling the ballast tanks. So now, we have a fair amount of water and less fuel.
How do you keep the tanks from corroding in the salt water? "The ballast tanks are concrete-lined and they have sacrificial zincs," explained Jeff. These zincs are common on ships in places that come in contact with salt water. The idea is that the corrosion takes place on the zinc instead of on the steel.
"It's also important to remember that the fuel and water are in separate tanks, so there is no mixing of fuel and water."
When we come into San Diego, the first order of business will be refueling at a fuel dock. This is an island-like platform with large containers of diesel fuel.
"We can take on 20,000 to 30,000 gallons of fuel per hour comfortably," said Jeff. "So, it'll take us about 4 to 5 hours to completely fill up."
This is no small task, because as the fuel is being added, the ballast tanks must be carefully pumped out. In this way, the ship will remain in the same position in the water. The ballast water has an interesting history.
"We need to exchange our ballast water in the open ocean, outside of 200 nautical miles, according to maritime regulations," explained Jeff.
Can you think why it is not permissible to dump water from one port (say Manzanillo, Mexico) into another port (like San Diego, California)? This is not an easy question, but the answer lies in the microscopic organisms living in the water. Atlantis and other ships that travel between ports could potentially carry organisms to new locations, introducing them to environments where they didn't exist before.
These organisms could potentially thrive in their new environment and take over and become invasive and out-compete the organisms that lived there (we call these native species). Since ballast water is one of the primary ways that this could happen, Atlantis and other ships are required to empty their ballast tanks and take on new water in the open ocean, which is believed to contain relatively few numbers of potentially invasive organisms. There are several other ways to minimize introducing new organisms, but this one seems to work well.
Isn't that fuel just going to sit in the tanks in Atlantis on the dock for a while?
"Right," said Jeff. "We add two things to the fuel. One is a treatment for the reduction of smoke when we burn it. The other is to control biological growth. If you let it sit for too long, this fungus will begin to grow."
Where will this fuel be taking Atlantis? Well, after we are unloaded, safely back ashore, Atlantis will begin preparing for its next adventure to Easter Island, off the coast of South America.