[gurps] underwater sails

[David Scheidt]

On Wed, Jan 14, 2009 at 12:14 AM, Susan Koziel
<kataryna_dragonweaver at yahoo.com> wrote:
> --- On Tue, 1/13/09, David Scheidt <dmscheidt at gmail.com> wrote:
>\\
> I still don't see how the density (g/L) has anything to do with it though. As I mentioned earlier I know there are creatures that use different currents to maneuver - whom ever mentioned that it means you have to move in the directions of the current is correct, but as long as that's where you want to go that's fine. IIRC this is something deep vent creatures use as a way to both move and maintain temperature.
> :)

That's not sailing.  that's just drifting.  Sailing is exploiting a
flow in a fluid to move you the direction you want, even if that's not
the direction of the flow.  You can only do that at the intersection
of two different fluids (air and water, in the case of a boat.)
Density difference is what provides the interface; without it, the two
layers will tend to mix, especially when you try to use a "keel".
Here's a pretty decent, though superficial explanation of some of the
physics.

http://www.physclips.unsw.edu.au/jw/sailing.html


> -Sue-damn it Jim I'm a Biologist not a Physisist
> PS: wind on their beam? (don't sail either - being rather land locked here) I thought that you turned the sails to catch the wind... but would like to know better.

you turn the sails depending on the direction, true.  but if they're
"catching" the wind, like your kite did on your skates, you only have
drag.  If the wind moves across them, you've got lift as well, and you
can go lots faster.  (fast boats can go two or three times the speed
of the wind, in fairly light winds.  they don't get much faster as the
wind increases, as the speed of a sailboat is limited to about the
square root of its length in feet, answer in knots.)


-- 
David Scheidt
dmscheidt at gmail.com