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

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