[gurps] underwater sails

[Susan Koziel]

--- On Tue, 1/13/09, David Scheidt <dmscheidt at gmail.com> wrote:

> > Well if you were an underwater creature you could use
> a sail like object to maneuver via placing a sail in a under
> tow or counter current, as there are water organisms that
> basically move like that....
> >
> > But not being personally a sailor type what the heck
> is an under water sail; and why do you need a density
> difference for a sail... doesn't a sail work because the
> wind fills it an pushes a vessel along a surface - and wind
> has a velocity that you are harnessing, and the surface has
> less resistance then the force the wind exerts over the area
> of the sail. Density of the wind or the water has nothing to
> do with it.
> 
> No.  You don't (generally) sail by letting the wind
> push the sail.
> The sail is an airfoil.  It generates lift.  (even downwind
> sails,
> like spinnakers generate more lift than drag)  The keel
> resists the
> sideways component of the lift's vector, and what's
> left is where you
> go.   With out a keel, you can only go straight down wind. 
> Real boats
> can go much faster with the wind on their beam.  (Actual
> angle depends
> on the boat, and how fast depnds on the boat, too.)
> 

See... It just shows I'm really not a physicist.
:)
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.
:)
-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.