Re: [Paddlewise] flow

Matt and John are discussing whether water is displaced sideways (Matt's
idea) or vertically (John's idea). To them I ask, why one or the other,
and not a combination of both? My intuition tells me that water is
displaced normal to the local surface of the hull, and probably in a
uniformly thick layer. At least for a smoothly varying hull. If each
parcel of water is not displaced in the normal direction, then water
pressure anomallies are created as the parcel collides with an adjacent
parcel in one direction, and leaves a void in the other direction. I would
further imagine that this effect is what creates extra drag and
initiates turbulence. A cylindrical hull would minimize this effect, and
so to those who know, I ask could this be why the fastest hulls are
more cyclindrical in cross-section? Of course sea kayaks aren't just
interested in pure speed and therefore are willing to sacrifice a little
speed for better handling. 

Another interesting question is what happens to the displacement direction
of water at a hard chine?

Cheers,
kevin
	 ___________________                                                            
	/   Kevin Whilden   \
       |Dept. of Geosciences ___
       |University of Washington \
       |kwhilden_at_u.washington.edu| 
        ________________________/                       

On Tue, 25 May 1999, John Winters wrote:

> These days I think this gets done mathematically since one doesn't mess up
> the tank or models.

Can this really be done mathematically? I thought that calculations of
flow for any object that moves on the interface to two different fluids
was extraordinarily difficult. If it can be done... how?

> 
> One of the things that impress me has to do with the similarity in flow
> lines for widely divergent hull shapes. The flow lines (crudely done with
> yarn I admit) I got on my sprint boats looked remarkably like those I got
> for my canoes and they looked remarkably like the ones Taylor got on his
> ship models.
> 
> Matt asked why I thought the flow would dive under the hull and I must
> answer "I don't know" but the evidence points to something other than water
> being pushed only to the side.
> 
> Cheers,
> John Winters
> Redwing Designs
> Specialists in Human Powered Watercraft
> http://home.ican.net/~735769/
> 
> 
> 
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