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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. Actually, bending stresses would be more of a concern, than the minor variation in draft from Tropical to Winter. If you've flown in turbulent weather you've watched a wing flex ..... imagine watching a whole hull doing that. otn |
On Thu, 17 Feb 2005 06:34:58 GMT, otnmbrd
wrote: Actually, bending stresses would be more of a concern, than the minor variation in draft from Tropical to Winter. If you've flown in turbulent weather you've watched a wing flex ..... imagine watching a whole hull doing that. My father, who turns 80 tomorrow, was in the British Merchant Marine during WWII. He said that while the losses from U-Boats were devastating, he found a lot of sailors feared the kind of storm that could "bridge" a single-hulled, laden freighter between two wave crests, causing it to fail and essentially snap in half. He said the ships rushed out in the latter half of the war were worse for this sort of thing, akin to the "Liberty ships" in the States. R. |
rhys wrote:
My father, who turns 80 tomorrow, was in the British Merchant Marine during WWII. He said that while the losses from U-Boats were devastating, he found a lot of sailors feared the kind of storm that could "bridge" a single-hulled, laden freighter between two wave crests, causing it to fail and essentially snap in half. He said the ships rushed out in the latter half of the war were worse for this sort of thing, akin to the "Liberty ships" in the States. R. The Liberties were one of the first ships massed produced with all welded construction. Initially, from memory, there was a serious problem with breaking in half. Much of this was corrected/lessened by adding a riveted plate (crack arrestor) around the hull at the main deck level. Again, from memory, this was considered a "stop gap" solution that seemed to have good results and in fact you tended to see these "crack arrestor" plates on much construction until well into the 60's. otn |
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 |
"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 |
In article . net,
otnmbrd wrote: rhys wrote: My father, who turns 80 tomorrow, was in the British Merchant Marine during WWII. He said that while the losses from U-Boats were devastating, he found a lot of sailors feared the kind of storm that could "bridge" a single-hulled, laden freighter between two wave crests, causing it to fail and essentially snap in half. He said the ships rushed out in the latter half of the war were worse for this sort of thing, akin to the "Liberty ships" in the States. R. The Liberties were one of the first ships massed produced with all welded construction. Initially, from memory, there was a serious problem with breaking in half. Much of this was corrected/lessened by adding a riveted plate (crack arrestor) around the hull at the main deck level. Again, from memory, this was considered a "stop gap" solution that seemed to have good results and in fact you tended to see these "crack arrestor" plates on much construction until well into the 60's. otn The Liberties that I've heard of were ferro-concrete and not particularly successful. We have a few of those grounded within our cruising grounds. -- Jere Lull Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD) Xan's Pages: http://members.dca.net/jerelull/X-Main.html Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/ |
Jere Lull wrote:
The Liberties that I've heard of were ferro-concrete and not particularly successful. We have a few of those grounded within our cruising grounds. Other than knowing there were a number of the "ferro" ships constructed, I have little info on them. I seem to remember there were one or two grounded above the Carquinez (sp?) bridge enroute to Martinez, Ca.. otn |
On Thu, 17 Feb 2005 20:02:51 GMT, otnmbrd
wrote: Again, from memory, this was considered a "stop gap" solution that seemed to have good results and in fact you tended to see these "crack arrestor" plates on much construction until well into the 60's I believe I recall seeing them years back on some of the older "LakeMax" frieghters here on Lake Ontario, which are limited to the lock size on the Welland Canal of about 750 feet.. R. |
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. |
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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