Re: [PSUBS-MAILIST] Bouancy (please read)

[MerlinSub@t-online.de (Carsten Standfuß)]

Hi Katie - I love this problem also..Its new for me..

There is another point - its geological.

The oceans with the high density saltwater like
the dead sea, the read sea, the black sea etc.
are near the aquator than the ocean with the freshwaters like
the baltic sea. And they gravity of the earth is not constant..
its about 9,78 m/s2 at the äquator and about 9,83 m/s2 on the
north- and south pole...

Also the watertempature in this high density
saltwaterareas is normaly higher than on the freswater areas
near to the North or South. But the wind blowes 
higher were ? I think on the Äquator areas..

Also the capicity to hold the temperature is higher in saltwater. 

But your are right in commercial ship tank test they made also
messuring of density of the water and the temperature. 

Unfourtunatly the scale problem with your model 
and the original cover (maybe) the small amount of effect. 
(means for your model the atoms of the water are bigger in scale
than for the original scale ship. So its creates other geometry of 
waves than the orignial ship.)

Lot work if you figures with so small effects..

Carsten - and if your sailboats sails in mercury it will capzied
without wind. 

Alec Smyth schrieb:
> 
> Katie,
> 
> I love this problem! But I disagree with Jonathan, who said:
> 
> "salt water should cause anything to be more
> bouyant, but it is also more dense which means
> the boat would have to plow through more matter
> than fresh water."
> 
> In fact, it is true that salt water is denser, but according to Archimedes'
> principle, the object will displace a lesser volume of it -- it does not
> plow through more matter in salt water. On the contrary, while the displaced
> mass is the same, the displaced volume of salt water is less, so the object
> might move FASTER in salt water due to less hidrodynamic drag.
> 
> If the object is moved by wind, whether by design (e.g., sailboat) or not
> (e.g., oil tanker cruising empty), you have to consider its DIRECTION OF
> TRAVEL relative to the wind. A sailboat for example can move with the wind,
> or against it. If it floats higher in salt water, you can argue that it will
> catch more wind and move faster... but only if the direction of movement is
> WITH the wind. If your sailboat is moving upwind, then floating higher will
> only slow it down.
> 
> If the object moves solely as a consequence of water currents, there isn't
> any difference between sweet and salt water.
> 
> Finally, I suggest you tell your instructor that the aswer depends on the
> WATER TEMPERATURE. You see, sweet water freezes slightly warmer than salt
> water. So if the temperature is just right, your salt-water boat will sail
> fine while the sweet-water equivalent will go nowhere at all.
> 
> :)
> 
> Alec Smyth
> 
> -----Original Message-----
> From: owner-personal_submersibles@psubs.org
> [mailto:owner-personal_submersibles@psubs.org]On Behalf Of Jonathan
> Wallace
> Sent: Monday, February 28, 2000 1:04 PM
> To: personal_submersibles@psubs.org
> Subject: Re: [PSUBS-MAILIST] Bouancy (please read)
> 
> Well, salt water should cause anything to be more
> bouyant, but it is also more dense which means
> the boat would have to plow through more matter
> than fresh water.  I'd guess that there may be
> a theoretical advantage to speed in salt water
> since drag would be less (less boat in the water),
> but I'd also guess the difference is imperceptable
> and possible immeasurable.
> 
> ok all you armchair scientists, have at it.
> 
> Jon