OPA 90, the legislation enacted after the Exxon Valdez incident mandated double hull technology, essentially wrapping a second hull around the first, on all newly built tankers. While this has been mostly effective and (had it been mandated for use on container ships) would have prevented last year’s San Francisco Oil Spill, it fails to protect the environment during catastrophic groundings. Mo Husain of MH Systems, Inc. has recently worked on perfecting alternative means of “loss of containment” prevention. He tells us:
CONCEPT MADE SIMPLE
Imagine a Straw…The underpressure concept is best understood by making an analogy with which most people can identify. Imagine sipping water half-way up through a straw and sealing off the top of the straw with your fingertip. A simple principle of hydraulics allows the water to be held in the straw at this level until the finger is released.
This same principle allows oil to be contained within the hull should a rupture occur in the tank. When a tanker is loaded, the oil level inside the tank is higher than the surrounding seawater level. This causes a higher pressure to exist inside the tanker due to hydrostatic pressure. Normally, when a hull is ruptured, the pressure inside forces oil to flow out up to the level of the surrounding seawater (discounting density). Using AUPS, this complete loss would not occur.
The system equalizes the pressure inside and outside the tanker at the rupture point by applying a slight underpressure of 2 to 4 psi in the ullage space of the tank. As oil flows out, it is replaced by seawater up to the rupture point only. Oil loss is held to a minimum as all oil above the rupture point will remain in the tanker. In the event of an accidental grounding bottom rupture, AUPS would prevent virtually all oil spillage from the tanker.
For a comprehensive look at this system click HERE and for the work Mo is doing on Ballast Water Treatment visit his company’s blog found HERE.
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4 responses so far ↓
1 OldSailor // Feb 1, 2008 at 6:53 pm
The concept is scientific and interesting. The cost of the ship also is expected to be lesser than double hull ships.
2 Robert Hart // Feb 1, 2008 at 10:02 pm
I noticed that the paper was written in 2004 and the test conducted in 2001, any word on what’s happened with the design since then?
3 John // Feb 2, 2008 at 2:09 am
Robert, I actually found this while researching Water Ballast Treatment solutions and found it interesting so we posted it. The truth is that after the Exxon Valdez ran aground their were a few alternatives to double hull design proposed by various parties. DH won out and now, nearly 20 years later, every layer of the industry has invested too much money for a change of this type to be done easily. That doesn’t mean we can’t gently remind them their are other, potentially better, ideas out there.
4 gertbue // Feb 3, 2008 at 11:22 am
AUPS, I gather, has a significant problem: inside a tanker’s hull free floating surfaces potentially inhibit a ship’s stability. I haven’t followed the discussion but I assume this is the reason why double hull prevailed.
However, neither AUPS nor DH can prevent a grounding. Another technology that was developed following Exxon Valdez pontentially can - ECDIS; it highlights and warns of charted shallow waters ahead. Unfortunately, the press seems not to take notice of it.
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