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#21
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#22
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#24
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I just did some research on this. Sea water density increases as it get
colder until the temperature hits 4 degrees celsius then expands until it freezes. So don't take a loaded boat too far north. JR Gilbreath wrote: Brian Are you sure about this. It would seem to me that the cold water would be less dense. It expands as it freezes. JR Brian Whatcott wrote: On 15 Feb 2005 14:34:42 -0800, wrote: Brian Whatcott wrote: After numerous ship losses, Plimsoll legislated a hull mark in Parliament, the "Plimsoll Line" which accounts for salt and fresh, warm n cool water, beyond which a commercial vessel must not be loaded. Unaccounted ship losses were much reduced thereafter. The difference between salt and freshwater displacement and waterlines makes sense to me, since the salt increases the density of the water, right? But why is there a difference between summer and winter? Thanks, Brent 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.... Brian Whatcott Altus OK |
#25
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In article .com,
wrote: Maybe I've killed too many brain cells over the years or just forgotten some basic stuff but my understanding of Archimedes Principle is that the buoyant force on an object is equal to the weight of the fluid it displaces. This means that my boat that weighs 8000 lbs must displace 8000 lbs of water in order to float. This is true and is a basic principle of floating objects. If she takes on 8000 lbs of water, she sinks cuz the buoyant force doesnt balance the weight. Right? I suspect that's false. Your boat may or may not have that much reserve buoyancy. Our 3.5 ton boat is rated to carry at least 5 tons. Would take somewhat more to sink her in calm water. Hull (without keel) is a bit more than a foot submerged. We have 3'+ more freeboard and the hull gets FAT up there. So, why do people make a distinction 'tween displacement and weight? Sounds better, and is more technically correct. Reminds me of a hairy old story: New engineer is told to find out how much more of something is on a barge. After hours of laborous measurements and calculations, the foreman comes by to see what the matter is and points out the numbers marked on the hull -- showing displacement. -- 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/ |
#26
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"JR Gilbreath" wrote in message
... I just did some research on this. Sea water density increases as it get colder until the temperature hits 4 degrees celsius then expands until it freezes. So don't take a loaded boat too far north. ----------snip------------ Winter displacement will be more affected by frozen spray than any variation due to temperature. Not to mention the required antifreeze for the crew. surfnturf |
#27
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We don't have to worry about frozen spray like you do but we still use
the antifreeze just to be on the safe side. surfnturf wrote: "JR Gilbreath" wrote in message ... I just did some research on this. Sea water density increases as it get colder until the temperature hits 4 degrees celsius then expands until it freezes. So don't take a loaded boat too far north. ----------snip------------ Winter displacement will be more affected by frozen spray than any variation due to temperature. Not to mention the required antifreeze for the crew. surfnturf |
#28
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Water is a rather unusual liquid. It gets more dense as it cools, then at 4 degreesC, it's as dense as it's going to get, and when cooled further, expands a little again. That's why water in cold lakes freezes from the surface down. When water turns to ice, it shows its other strange characteristic - it REALLY expands. That's what does for your outside copper pipes. Brian Whatcott On Tue, 15 Feb 2005 20:56:25 -0500, JR Gilbreath wrote: Brian Are you sure about this. It would seem to me that the cold water would be less dense. It expands as it freezes. JR Brian Whatcott wrote: On 15 Feb 2005 14:34:42 -0800, wrote: Brian Whatcott wrote: After numerous ship losses, Plimsoll legislated a hull mark in Parliament, the "Plimsoll Line" which accounts for salt and fresh, warm n cool water, beyond which a commercial vessel must not be loaded. Unaccounted ship losses were much reduced thereafter. The difference between salt and freshwater displacement and waterlines makes sense to me, since the salt increases the density of the water, right? But why is there a difference between summer and winter? Thanks, Brent 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.... Brian Whatcott Altus OK |
#29
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As someone has said, the WNA marking is mainly related to weather and is
applied to ships below a certain length above a specific latitude. The basic idea being to allow some minor additional freeboard as a safety factor. There are a number of these draft markings, all the way to Tropical Fresh which are mainly used when loading at a specific locale and going to another, to give you a basis as to how deep you can load, as you can't be below the draft requirements at the next port. Regarding markings on the side of a barge ..... I've never seen any denoting displacement, however, reading the draft is a quick and easy way to know how much cargo (weight) has been loaded. otn |
#30
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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. |
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