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#1
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On Thu, 17 Feb 2005 00:13:16 -0500, rhys wrote:
On Wed, 16 Feb 2005 01:40:22 GMT, Brian Whatcott wrote: Warm water is less dense than cold water. Water expands more with temperature than the metals, so a ship sits lower in hot water. Moreover, water's rate of expansion increases as the temperature rises. Another factor: water like oil, gets considerably less viscous when warm, so a hull might be expected to be livelier, and maybe the swell higher.... So the worst case scenario for a loaded ship would be a laden tanker enduring a Red Sea or a Persian Gulf cyclone? I vaguely remember that those areas are the hottest oceanic bodies on Earth. By contrast, on a calm day in zero C. Antarctic water (ice-free, however), the same laden ship would ride high(er) and dry. Interesting! R. You actually contributed another gotcha: a crude oil cargo runs thin and expands, so the CofG would go up a little higher while the freeboard goes down, in the Gulf. Brian Whatcott ALTUS ok |
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#2
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"Brian Whatcott" wrote in message ... On Thu, 17 Feb 2005 00:13:16 -0500, rhys wrote: On Wed, 16 Feb 2005 01:40:22 GMT, Brian Whatcott wrote: Warm water is less dense than cold water. Water expands more with temperature than the metals, so a ship sits lower in hot water. Moreover, water's rate of expansion increases as the temperature rises. Another factor: water like oil, gets considerably less viscous when warm, so a hull might be expected to be livelier, and maybe the swell higher.... So the worst case scenario for a loaded ship would be a laden tanker enduring a Red Sea or a Persian Gulf cyclone? I vaguely remember that those areas are the hottest oceanic bodies on Earth. By contrast, on a calm day in zero C. Antarctic water (ice-free, however), the same laden ship would ride high(er) and dry. Interesting! R. You actually contributed another gotcha: a crude oil cargo runs thin and expands, so the CofG would go up a little higher while the freeboard goes down, in the Gulf. Brian Whatcott ALTUS ok G Not all crudes are "thin", and many cool down after loading, but these amounts (change in ullage) tend to be very small. Couple this with the fact that tanker GM's when loaded are normally VERY high, the degree of change in ride, be it comfort or submergence due to water temps in salt water, will not be noticed. otn |
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#3
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On Fri, 18 Feb 2005 00:13:54 GMT, Brian Whatcott
wrote: You actually contributed another gotcha: a crude oil cargo runs thin and expands, so the CofG would go up a little higher while the freeboard goes down, in the Gulf. You're right: I wasn't factoring in the nature of the cargo. I wonder if the viscosity of the oil (and its tendency to slosh in tanks) would also affect stability in this scenario. I seem to recall the phrase "surface effect" or some such factor relating to liquid cargo causing ships to capsize unexpectedly, or at least before it was theoretically anticipated. R. |
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#4
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rhys wrote:
You're right: I wasn't factoring in the nature of the cargo. I wonder if the viscosity of the oil (and its tendency to slosh in tanks) would also affect stability in this scenario. Tankers tend to have the majority of tanks divided into three separate tanks (i.e., 1P, 1C, 1S) and when loaded, the ullage will be very close to the top of the tank, so that any sloshing almost immediately pockets. Without going into a long discussion, this fact coupled with the large amount of stability, tends to negate the affects on stability. I seem to recall the phrase "surface effect" or some such factor relating to liquid cargo causing ships to capsize unexpectedly, or at least before it was theoretically anticipated. "Free surface effect". It's what caused the car carrier which recently sank after a collision, to roll over so quickly. Again, not normally a problem with tankers, unless they have double bottoms which are open port to stbd. otn |
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