## Re: An Idea ...

Expand Messages
• Peter, see below ... By definition is not the same as as measured in a wind tunnel . As measured in a wind tunnel, a foil with an AR of 1 has measurably
Message 1 of 77 , Dec 1, 2005
Peter, see below

--- In boatdesign@yahoogroups.com, "pvanderwaart" <pvanderwaart@y...> wrote:
>
> > In spite of the fact that fin keels have a smaller "lift"
> > and stall out more quickly with almost no residual lift,
> > they are preferred by racing designers because they have
> > more lift at lower angles of attack (which means they can
> > sail closer to the wind)...
>
> It's true that a stalled fin has little lift. Everything else I
> disagree with.
>
> 1) Before you can say that a fin has smaller lift, you have to
> establish some measure of equivalent size. On a sailboat, the size is
> determined by the amount of lift required, so different keel options
> have equal lift and therefore equal equivalent size, by definition.
>
"By definition" is not the same as "as measured in a wind tunnel".

As measured in a wind tunnel, a foil with an AR of 1 has measurably lower lift than a foil with an AR of 6 with the same area and at the same angle of attack, as long as it is not stalled out.

In actual practice, however, the low AR foil (keel, sail) usually has significantly greater area than a high AR foil on the same sized boat, making a comparison of the two a comparison of apples with oranges.

> 2) High AR foils are preferred by designers because they have high L/D
> ratios. Since the lift is a design constant (see above), it's the low
> drag that they are looking for.
>
This is also true, and I have already mentioned it using different words.

> 3) The well-designed boat with a low AR keel will be able to sail just
> as close to the wind as it's neighbor with a high AR keel, but it will
> be slow (see above). It may even be slow enough that it pays to sail
> at a lower angle where less lift will be required, and the drag
> penalty is less.
>
The low AR keel is usually larger, therefore has more surface drag as well as greater L/D drag, as I have mentioned before.

Except for point 1) above, I think we agree on most points.

T. Lee.
• ... We *DO*, however, have some partial Egyptian linen sails from way back. No kidding, some mummies have been unwrapped, and the fabric was recycled from used
Message 77 of 77 , Dec 3, 2005
--- Tord Eriksson <tord@...> wrote:
>
> But, as far as I know, no sail from that era exist
> (we have some clothes,
> that's about it, and (weaving) reeds, out of bone
> and possibly wood material.
>
> So it is essentially just speculations ...

We *DO*, however, have some partial Egyptian linen
sails from way back.

No kidding, some mummies have been unwrapped, and the
fabric was recycled from used sails. This is known
from matching up seams, stains, and so forth.

I don't know the rigging that was disclosed from this,
if any.

-Lew

------------------------------------------
"If your only tool is a hammer, everything
starts to look like a nail."
- Anon
------------------------------------------

__________________________________