Let's not forget we are judging a 1971 design with a 2008 eye and comparing
it to a computer generated keel profile. Many fast keel shapes have come and
gone in that timeframe.
C270 in 1993 was the CAD generated design. Now that I've said that it could
have been the Catalina 37 Congressional Cup Boats based on when the designer
joined the firm.
I had a morphed a Compu Keel profile into a template profile that faired a
C22 swing keel and remained within class rules back in 1993. We liked the
results but the boat wanted to sailed a little differently in various
conditions. The boat was also flipped long boarded and an epoxy - Teflon
bottom was applied to all underwater surfaces. She wasn't unbeatable but we
always new when we screwed it up.
Phil Agur C270 Wing Tip
Secretary, Call Sign WCW3485
IC27/270A MMSI 366901790
www.catalina27.org Vessel Doc# 1039809
----- Original Message -----
From: "David Shugarts" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Monday, March 17, 2008 8:51 AM
Subject: Re: catalina27-talk: Keel Fairing
Hi, Tim--
I think your summation of it as "like a Chevy" is a pretty good analogy.
To
go back to the source, I have now heard Frank Butler answer a number of
sophisticated questions with what sure sounded like naivete to me, so I
have
a hunch that our factory keel section was a "oh, whatever" decision at the
time. Then these better keel sections would naturally be an improvement,
but
only because the bar was set so low.
It would be interesting to hear from an expert here, because I just feel
as
though the designers of the cool toys are way beyond NACA foils. Or
perhaps
they really are more about the bulb than the keel section itself. For
instance, if we could hang a heavy lead bulb on a carbon fiber keel, we
would probably do it, and we might find that ANY keel foil would be fine
for
the purpose.
BTW, this link: http://www.hanleyinnovations.com/glossary.html, shows a
few
cases where the NACA 0012 was used in aircraft, but it also shows that
some
venerable aircraft (e.g., the Cessna 150/152) had one foil at the wing
root
and another at the tip (in other words, more sophisticated). Notably, the
B-17 Flying Fortress had it as the root foil (love that airplane!).
Regards,
Dave S.
On 3/17/08 12:03 AM, "[EMAIL PROTECTED]" <[EMAIL PROTECTED]> wrote:
I don't profess to have any knowledge whatsoever when it comes to fluid
dynamics, I have just been going on threads on SA and bits and pieces of
knowledge that I've read from different designers.
I think that as far as high performance (e.g., sport boats, hulls that
will plane
off the wind) sailboats are concerned, a bulb on a keel foil is pretty
much the
name of the game. Certainly heavy displacement and cruising boats will
look toward other keel configurations. But the NACA foils offsets have
pretty
much been determined to be the go-to configurations for fast keel struts
in the sportboat world. There are a few arguments over whether a 0011
section
might be faster than a 0012 seciton (with a resulting decrease in
strength/robustness
to loads, etc) for example, but the 0012 shape seems to be the chevy
pickup when
it comes to most foil sections below the waterline.
These are fairly simple shapes. Pretty easy for an amateur to cut with a
hot wire,
or for a CNC machine to do it.
(http://www.youtube.com/watch?v=q7uvq4RlhHM)
I can certainly imagine that areonautical designers would have the need
to
come up
with more complex shapes for specialized, shape-specific demands,
executed
at high speed with enormous G-force loads in the atmosphere, and new
materials and production techniques would allow for a huge amount of
variability when it comes to foil offsets these days.
But these are just simple symmetrical foils shapes that you can order up
and get made pretty cheaply on-line...I just ordered a 54" piece of
spyderfoam cut to NACA0012 sections,
for about a hundred bux incl. delivery. It's a dream-world out there now
for home boat (or aircraft) builders!
tf
My ears perk up here. First, I confess ignorance. Are boat keels based
on
NACA foils, and do they apply to water, as opposed to air? Perhaps there
was
a series of NACA foils intended for water? I just never paid attention
to
that part of things, although I studied NACA airfoils for my own
purposes
many years ago. I vaguely recall a factor called Reynolds Number that
would
govern foils in various media, such as air and water. Can you elaborate?
Regards,
Dave S.
PS--I was just a layman studying the foils at the time, but I went
through
them all pretty carefully. It seemed to me that they were kind of
empircal
in nature. I got the impression that the great virtue of a NACA foil,
for
an
aircraft designer of the 1930s or 1940s, was that it was thoroughly
tested
and predictable. However, it seemed as though a lot of developments of
later
decades, such as the Clark-Y, not to mention variable sweeps and tapers,
variable chords and foils in a given wing, etc., began to favor
departures
from the NACA foils (except when mere predictability was the goal, as in
vertical stabilizer foils). So, although I later got into aviation
writing
and was constantly looking for NACA foils, I didn't find many in the
wings
of light aircraft. In my time, we saw NASA come out with the GAW-1, and
I
have always assumed that later, composite aircraft designers were free
to
work with an infinitely variable foil in mind.
On 3/16/08 8:40 PM, "[EMAIL PROTECTED]" <[EMAIL PROTECTED]> wrote:
but they also value every advantage they can get.
key words^, huh?
nice explanation, Chris.
So I guess Compu-Keel is still around?
http://www.compukeel.com/
odd because you get NACA foil specs on-line for free...but I guess all
class
legal keels cant be derived from NACA sections.
tf
