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

["Karl & Shirin Fuller" <fullerk@voyager.co.nz>]

Katie,
My understanding is this.
There are two main reasons for there to be resistance of a hull in a fluid.
The first is drag due to surface area drag, the greater the wetted area, the
greater the drag. Round hulls have low drag but little form stability due to
shape. The second is due to hull form or shape. Plotted on a graph, these
two causes will change places for low speed and high speed. At low speed,
the significant cause of resistance is wetted area and conversly, at close
to hull speed, the shape will take over as being the greatest cause of drag.

As has been mentioned, The yacht will displace less in salt water and
therefore, at lower speeds, there will be less frictional drag, I believe.
But at higher speeds this will it seems reduce as the significant form of
drag. The drag induced by shape at higher speeds my differ only minutely as
the yacht is moving less volume of water aside in salt water but it has a
mass equal in theory  to the greater volume of fresh water.

I agree with Carsten, imagine an extreme or test extremes and the results
should be easier to detect.

Hope I've helped,
Karl.
> Hi,
>  This may seem silly to you and you might not even
> read it but here it goes:
>     I'm in the eighth grade and I am searching for
> research for the completion of my science project. My
> Problem Statement is "Will a buoyant object, such as a
> sailboat go faster in salt water or fresh water?". I
> have been researching water, salt, sailboats, and
> wind. I stumbled upon your email when attempting to
> research buoyancy. I am not sure,though, if I am
> researching the right topics. Do you have any helpful
> information on the effect buoyancy has on the speed of
> a sailboat? Or do you have any helpful research
> information or topics?
>     Further information on my experiment procedures:
>        I'm using a toy sailboat and placing it in two
> different gutters, one containing fresh water and one
> containing salt water. At one end I'm going to place a
> box fan on high and time the boat untill it reaches
> the other end of the gutter.
>   Thank you if you read this. Your help will make my
> research more complete. I assure you the time,if any,
> you use to help my will be useful in my experiment.
>                                   Thank You,
>                                  Katie O'Bryan
> __________________________________________________
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