[Rhodes22-list] Windage

[Ronald Lipton]

Bill,

  Now you are shooting geese in a barrel.  Windage only should depend on 
area facing
the wind. It's basically area (including spars ...) times a drag coefficient 
(one for a flat plate).
To the extent that the hull area facing the wild also increases with lenght 
there may be
a correlation, but it is not direct.

 I would guess the masts and rigging have a significant effect, especially 
since the wind
velocity increases with height and pressure goes like velocity squared.  (By 
the way
this is the same sort of boundary layer effect as in the teacup, but 
extended over
a larger area.  There is even an analogous flow pattern.  Air near the 
surface moves
in toward the center of a low, causing an upward flow near the center of the 
low -
just like the teacup!).  In addition if the boat sways in the wind the 
effective pressure
on the anchor will also increase.

Ron

----- Original Message ----- 
From: "Bill Effros" <bill at effros.com>
To: "R22 List" <rhodes22-list at rhodes22.org>
Sent: Thursday, January 19, 2006 10:31 AM
Subject: [Rhodes22-list] Windage


> Ron,
>
> Continuing from my previous post, but changing the subject line, when you 
> have time I would love to understand the common "windage" calculations.
>
> I see statements like "when you double the length of a boat, windage 
> causes the load on the anchor to increase 4 times".  Why would that be?
>
> Boats on anchor face into the wind--when the wind hits them broadside, 
> they swing so that they again face into the wind.  The boats swing long 
> before the increased load on the anchor becomes any kind of issue.
>
> It is hard for me to believe that a 44 foot long racing scull on anchor 
> will ever put more load on the rode than my 22 foot long, 8 foot wide 
> Rhodes.
>
> I could understand if doubling the beam squares the load.  It seems 
> logical that more freeboard means more windage.  I can buy that wind 
> dragging over a longer hull increases the load -- but doubles it?  That I 
> can't understand.
>
> The guy who used to sink anchors for a living in my cove once told me that 
> my mushroom anchor mooring would hold a battleship in less than 25 kt. 
> winds, and that people sinking bigger and bigger anchors "for safety's 
> sake" just didn't understand that what they already had was more than they 
> would ever need.
>
> Any insight you might have here would be appreciated--whenever you can get 
> to it.
>
> Bill Effros
>
>
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