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From: Larry N. Brown (no email)
Date: Sat Apr 21 2007 - 07:57:09 EDT
> Sorry, I'm not following you. By definition the projected area is the
> cross
> sectional area perpendicular to the wind. Anyway, if you are at anchor,
> the
> boat should head up in to the wind, no?
>
> Regards,
>
> --Jim
There's at least one other big fly in the ointment as pointed out in Hinz's
book on anchors and anchoring. The boat does not always head up into the
wind at anchor. It tacks, constantly exposing more than the simple frontal
profile. Say your boat sticks out of the water 10' and has a 12' beam.
Depending on the aerodynamic shape of the boat, it presents roughly 120 sq.
feet of "flat plate" drag. (Hull form may reduce this but this is a
conservative number.)
Now, say your boat yaws 20d to the wind. To the wind, your original 120 sq
ft will apparently shrink a little due to the angle but you will now be
exposing a portion of the side of the 40' hull as well. The greater the yaw,
the greater the load.
Calculate the worst case scenario and figure your anchor size. Then, to
paraphrase Ted G, go up at least one anchor size. Wayne Flatt on Skinwalker,
a 49' (I think) boat has a 75# SuperMax and he says he wishes he'd gone up
one size.
Regards,
Larry & Teri Brown
MV Cigano, 47' Prairie Sundeck
Still glued to the dock in Covington, LA
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