Re: [bolger] Re: box keel and centerboard
Without conceding the number that could dance on the point I would like
to point out the subject under discussion was how many can dance on the
head.
I would also like to say that there are few groups on the web that could
discuss a subject so earnestly with out rancor.
HJ
snip
to point out the subject under discussion was how many can dance on the
head.
I would also like to say that there are few groups on the web that could
discuss a subject so earnestly with out rancor.
HJ
snip
> In the meantime, I think only one angel can dance on the point of a pin ;>)
>
>John T
>
>
>
>
>
see below
instance, the NACA 009, the drag is considerably higher. At least from
Reynold's numbers of 100,000 on up. Not completely definitive in this
data below that number.
> craig o'donnell wrote:Agreed. More or less.
>
>>>
>>>Therefore it seems to me that flat sided rudders would be more
>>>effective as they create more resistance = better turning force. Flat
>>>sided keels like MICRO prevent more resistance to side slipping.
>>
>>
>
>The short answer is "no", flat plats can generate lift, but over a very
>limited range of angles.
>
> On the other hand a thin flat plate at 0-degreesNot true. I have a book with wind tunnel data. As compared to, for
>creates less drag than a foil.
>
instance, the NACA 009, the drag is considerably higher. At least from
Reynold's numbers of 100,000 on up. Not completely definitive in this
data below that number.
> This seems to be why kayakers, who could
>certainly have foil rudders if they wanted them, cling to thin aluminum.
> -- Craig O'Donnell Sinepuxent Ancestors & Boats
>
There is no doubt that airfoil shaped rudder and centerboard (or lee board, or dagger board) works better than flat plates. The extremely popular Laser is an example, and illustrates some of the problems with this approach. The Laser uses anairfoil in its daggerboard and the board fits precisely into the molded daggerboard well. This holds the board in alignment with the center of the hull. The daggerboard does not, of course pivot. This is a simple, effective way to locate the board.
If the board is to pivot, either in a centerboard well or as a leeboard, the mechanics get pretty complicated, and the possibilities for the airfoil getting out of alignment increase.
We build boats to suit ourselves. And if playing with airfoil shaped blades is what suits you, go for it. There are several development classes (moth, international sailing canoe and C-cats come to mind) where there may be significant gains to be had in this area. Since I build simple, relatively slow boats with less than state of the art rigs, I'll use flat plate foils with rounded leading edges, tapered trailing edges (less chatter that way), with enough area so they don't stall too easily at low speeds, and take whatever penalty results from surface area drag. If I were a racer (I'm not) or playing with a planing sailboat, I might take a different position. In the meantime, I think only one angel can dance on the point of a pin ;>)
John T
If the board is to pivot, either in a centerboard well or as a leeboard, the mechanics get pretty complicated, and the possibilities for the airfoil getting out of alignment increase.
We build boats to suit ourselves. And if playing with airfoil shaped blades is what suits you, go for it. There are several development classes (moth, international sailing canoe and C-cats come to mind) where there may be significant gains to be had in this area. Since I build simple, relatively slow boats with less than state of the art rigs, I'll use flat plate foils with rounded leading edges, tapered trailing edges (less chatter that way), with enough area so they don't stall too easily at low speeds, and take whatever penalty results from surface area drag. If I were a racer (I'm not) or playing with a planing sailboat, I might take a different position. In the meantime, I think only one angel can dance on the point of a pin ;>)
John T
----- Original Message -----
From: Lincoln Ross
To:bolger@yahoogroups.com
Sent: Friday, September 24, 2004 11:31 AM
Subject: [bolger] Re: box keel and centerboard
The keel on many boats is so low aspect ratio that you'd only get a
small gain from going to a real foil. By the time you got to a decent
lift coefficient, the induced drag because of the short keel (and
therefore low aspect ratio) would murder you. I suppose you could go to
a smaller fin with a flap on the back, but that might be fragile and
certainly would be complicated, and the drag of the hull might mask the
advantage. OTOH, if you went to a full foil you'd have a nice cool place
to put all that beer. You'd need a dividing membrane so you could fill
the empty space with water after using the beer, or the Micro would
float high.
I might be wrong, but my intuition is that sail shape is important for
two reasons:
1. It's hard to have enough area.
2. those sharp leading edges will stall if not set up just right.
I think the main criterion for sails is probably maximum lift
coefficient, becase of 1 above. Of course you also want to get that max
Cl at a low angle of attack for windward work, so as not to give up too
much pointing.
But I haven't the formal analysis to be sure about the above.
>Peter Lenihan wrote:
>I've really enjoyed reading about the finer details of what makes
>for a good centerboard/leeboard. However,I wonder if what is bellow
>the waterline is all that important compared to the sails? That
>is,for our type of boats you could probably get away with using the
>kitchen table for a means of lateral resistance and that would work
>fine.....just not too sure the same could be said if one were to use
>the living room drapes for sails.
>Looking forward to some informative disscusions/exposé on sail
>shapes and drive,especially after I think about how well the Micro
>performed with her slab-side-couldn't-spell-foil-if-it-was-paid-for
>ballast keel
>
>
>Thanks!
>
Bolger rules!!!
- no cursing, flaming, trolling, spamming, or flogging dead horses
- stay on topic, stay on thread, punctuate, no 'Ed, thanks, Fred' posts
- Pls add your comments at the TOP, SIGN your posts, and snip away
- Plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA, 01930, Fax: (978) 282-1349
- Unsubscribe:bolger-unsubscribe@yahoogroups.com
- Open discussion:bolger_coffee_lounge-subscribe@yahoogroups.com
Yahoo! Groups Sponsor
ADVERTISEMENT
------------------------------------------------------------------------------
Yahoo! Groups Links
a.. To visit your group on the web, go to:
http://groups.yahoo.com/group/bolger/
b.. To unsubscribe from this group, send an email to:
bolger-unsubscribe@yahoogroups.com
c.. Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.
[Non-text portions of this message have been removed]
Bruce,
Thank you, I will dig through the archives. As to fins/foils, this is VERY
interesting. Many arguments are made in regards to surfboards (admittedly
traveling
faster than your average sailboat, but in the same ballpark) and the most
appropriate fin/foil/placement combinations. School is in session and my
ears are open.
Sincerely
Darren
"Be sure to read back through the archived messages,
we have discussed Birdwatcher thoroughly already!
...and are presently discussing how many angels can
dance on the head of a Birdwatcher fin, and what the
logo said on the hat Phil Bolger was wearing when he
sailed in it."
_____
Yahoo! Groups Sponsor
ADVERTISEMENT
<http://us.ard.yahoo.com/SIG=1292ov1bh/M=298184.5285298.6392945.3001176/D=gr
oups/S=1705065791:HM/EXP=1096130053/A=2319498/R=0/SIG=11thfntfp/*http:/www.n
etflix.com/Default?mqso=60185352&partid=5285298> click here
<http://us.adserver.yahoo.com/l?M=298184.5285298.6392945.3001176/D=groups/S=
:HM/A=2319498/rand=308275123>
_____
Yahoo! Groups Links
* To visit your group on the web, go to:
http://groups.yahoo.com/group/bolger/
* To unsubscribe from this group, send an email to:
bolger-unsubscribe@yahoogroups.com
<mailto:bolger-unsubscribe@yahoogroups.com?subject=Unsubscribe>
* Your use of Yahoo! Groups is subject to the Yahoo!
<http://docs.yahoo.com/info/terms/> Terms of Service.
[Non-text portions of this message have been removed]
Thank you, I will dig through the archives. As to fins/foils, this is VERY
interesting. Many arguments are made in regards to surfboards (admittedly
traveling
faster than your average sailboat, but in the same ballpark) and the most
appropriate fin/foil/placement combinations. School is in session and my
ears are open.
Sincerely
Darren
"Be sure to read back through the archived messages,
we have discussed Birdwatcher thoroughly already!
...and are presently discussing how many angels can
dance on the head of a Birdwatcher fin, and what the
logo said on the hat Phil Bolger was wearing when he
sailed in it."
_____
Yahoo! Groups Sponsor
ADVERTISEMENT
<http://us.ard.yahoo.com/SIG=1292ov1bh/M=298184.5285298.6392945.3001176/D=gr
oups/S=1705065791:HM/EXP=1096130053/A=2319498/R=0/SIG=11thfntfp/*http:/www.n
etflix.com/Default?mqso=60185352&partid=5285298> click here
<http://us.adserver.yahoo.com/l?M=298184.5285298.6392945.3001176/D=groups/S=
:HM/A=2319498/rand=308275123>
_____
Yahoo! Groups Links
* To visit your group on the web, go to:
http://groups.yahoo.com/group/bolger/
* To unsubscribe from this group, send an email to:
bolger-unsubscribe@yahoogroups.com
<mailto:bolger-unsubscribe@yahoogroups.com?subject=Unsubscribe>
* Your use of Yahoo! Groups is subject to the Yahoo!
<http://docs.yahoo.com/info/terms/> Terms of Service.
[Non-text portions of this message have been removed]
> Darren Pearce wrote:Be sure to read back through the archived messages,
> newbie...Would love to
> hear more on BW.
we have discussed Birdwatcher thoroughly already!
...and are presently discussing how many angels can
dance on the head of a Birdwatcher fin, and what the
logo said on the hat Phil Bolger was wearing when he
sailed in it.
see below
keel.
tasks, then you can get bogus results. But the sail doesn't know it's
not a wing. WHether it's used horizontally or vertically doesn't really
make any difference. THey are all devices that produce lift, i.e. force
perpendicular to the flow, and the fluid mechanics are closely related.
snip
jumping machines, then.
get a sideways force, you will just slide to leeward.
They will work better SLOWER than a flat plate.
the game as your foils are stalled. Like the difference between an old
round parachute and a glider or aircraft.
symmetrical and assymetrical foils.
doesn't matter. Foils don't know from "speed of movement". What they
know about (i.e. change behavior as a result of) are Reynold's number
and angle of attack. On the Insolent 60, these are probably comparable
to slow aircraft. I recall, from running the numbers, that the US1M
Reynold's numbers, going at maybe 1 or 2 knots, are comparable to medium
and small model aircraft. So I'd suspect the I60 Reynold's number would
be comparable to a small but man-carrying aircraft.
snip
P.S. Reynold's number relates speed, viscosity, density and size as a
measure of how important viscosity is, as oppose to how important
kinematic forces are. Greater speed, density, and size favor kinematics,
>"Nels" wrote:Actually, almost any centerboard is high aspect ratio comparted to a box
>snip
>
>The type of keel combination I am referring to is exemplified by COL.
>HASLER, FIJI, ALERT. An original "box keel" example is MICRO
>according to PCB - with the keel box extending out to the bilges and
>a low aspect fin added:-)
>
>Of course centerboards can be either low or high aspect. I have
>always been intrigued by the 25 foot lapstrake CHEBACCO which has a
>shallow bulb keel, and a 3/8" thick 60 pound flat cut centerboard.
>
keel.
>If one does just mindless analysis without looking at the different
>Mr. Bolger also cautions about comparing centerboards AND sails to
>airplane wings. Their functions are in no way similar, unless used
>horizontally like the swing-wing keel of the I60, or the end plates
>on some of the rudders.
>
tasks, then you can get bogus results. But the sail doesn't know it's
not a wing. WHether it's used horizontally or vertically doesn't really
make any difference. THey are all devices that produce lift, i.e. force
perpendicular to the flow, and the fluid mechanics are closely related.
snip
>Aircraft wings create lift by being curved and asymetrical in cross-I guess almost all serious aerobatic planes are just very efficient
>section.
>
jumping machines, then.
>To create lift at very low speeds they require slots andNo lift = only leeway and no windward ability whatsoever. If you can't
>flaps and other attachements to cause even greater asymetery. I have
>never seen this used in keels and see no reason why one would want
>lift in a keel whose function is to prevent leeway.
>
get a sideways force, you will just slide to leeward.
>Are thereNACA foils are a lot fatter than the ply daggerboards, rudders, etc.
>asymetric keel cross sections? Slender NACA foils would stall out at
>the speeds our sailboats move wouldn't they?
>
They will work better SLOWER than a flat plate.
>If you're talking about resistance instead of lift, you've already lost
>Therefore it seems to me that flat sided rudders would be more
>effective as they create more resistance = better turning force. Flat
>sided keels like MICRO prevent more resistance to side slipping.
>
the game as your foils are stalled. Like the difference between an old
round parachute and a glider or aircraft.
>These are also used on aircraft and in other places, along with both
>End plates on rudders prevent vorticies off the end of the rudder and
>direct the water against the flat side of the rudder.
>
symmetrical and assymetrical foils.
>If you restrict yourself to low Mach aircraft, compressibility really
>Nels
>
>Message: 19
> snip
>--- Inbolger@yahoogroups.com, Mark <marka@h...> wrote:
>
>
>>>> > The Bolger swing wing has a completely flat top and a curved
>>>> > underside. This would create lift in my view, and therefore less
>>>> > wetted surface on the hull as the boat accelerates.
>>>
>>>
>>>
>>> If that wing worked on aircraft principles wouldn't it pull the
>>
>>
>boat down into the water,
>
>
>>> since an airplane wing is curved on top?
>>> Mark
>>
>>
>
>That is why I don't think you can compare them. The differences are
>first, that the speed of movement is no way near the same and
>secondly, air compresses but water doesn't.
>
doesn't matter. Foils don't know from "speed of movement". What they
know about (i.e. change behavior as a result of) are Reynold's number
and angle of attack. On the Insolent 60, these are probably comparable
to slow aircraft. I recall, from running the numbers, that the US1M
Reynold's numbers, going at maybe 1 or 2 knots, are comparable to medium
and small model aircraft. So I'd suspect the I60 Reynold's number would
be comparable to a small but man-carrying aircraft.
snip
P.S. Reynold's number relates speed, viscosity, density and size as a
measure of how important viscosity is, as oppose to how important
kinematic forces are. Greater speed, density, and size favor kinematics,
On the models, so called "laminar" foils are popular, but it turns out a
6% or 7% section, elliptical in front to about 23% chord andd straight
after that is better and very similar to some foils Mark Drela came up
with for model airplane tails. At least that's what I got from working
with Mark's program, Xfoil. For our full sized boats, some of the
laminar foils would be fine, as long as you could build with the
precision of a machinist and clean the foil before each race, and
reprofile every few months due to changes in the epoxy. (Full size
sailplane guys sometimes do this.). Otherwise, old NACA stuff like the
010 would probably be just fine for full size, though I suppose there
might be some sections just a little better.
6% or 7% section, elliptical in front to about 23% chord andd straight
after that is better and very similar to some foils Mark Drela came up
with for model airplane tails. At least that's what I got from working
with Mark's program, Xfoil. For our full sized boats, some of the
laminar foils would be fine, as long as you could build with the
precision of a machinist and clean the foil before each race, and
reprofile every few months due to changes in the epoxy. (Full size
sailplane guys sometimes do this.). Otherwise, old NACA stuff like the
010 would probably be just fine for full size, though I suppose there
might be some sections just a little better.
>Howard Stephenson wrote:
>snip
>Slender NACA foils sections are often used on sailboats, as a quick
>Google search will show you. To be competitive in some of the model
>classes e.g. US1metre, it's necessary to have an exceedingly thin
>fin. Model boats move very slowly when compared with airplanes, but
>the fins are in a much denser medium than air.
>
>Howard
>
The keel on many boats is so low aspect ratio that you'd only get a
small gain from going to a real foil. By the time you got to a decent
lift coefficient, the induced drag because of the short keel (and
therefore low aspect ratio) would murder you. I suppose you could go to
a smaller fin with a flap on the back, but that might be fragile and
certainly would be complicated, and the drag of the hull might mask the
advantage. OTOH, if you went to a full foil you'd have a nice cool place
to put all that beer. You'd need a dividing membrane so you could fill
the empty space with water after using the beer, or the Micro would
float high.
I might be wrong, but my intuition is that sail shape is important for
two reasons:
1. It's hard to have enough area.
2. those sharp leading edges will stall if not set up just right.
I think the main criterion for sails is probably maximum lift
coefficient, becase of 1 above. Of course you also want to get that max
Cl at a low angle of attack for windward work, so as not to give up too
much pointing.
But I haven't the formal analysis to be sure about the above.
small gain from going to a real foil. By the time you got to a decent
lift coefficient, the induced drag because of the short keel (and
therefore low aspect ratio) would murder you. I suppose you could go to
a smaller fin with a flap on the back, but that might be fragile and
certainly would be complicated, and the drag of the hull might mask the
advantage. OTOH, if you went to a full foil you'd have a nice cool place
to put all that beer. You'd need a dividing membrane so you could fill
the empty space with water after using the beer, or the Micro would
float high.
I might be wrong, but my intuition is that sail shape is important for
two reasons:
1. It's hard to have enough area.
2. those sharp leading edges will stall if not set up just right.
I think the main criterion for sails is probably maximum lift
coefficient, becase of 1 above. Of course you also want to get that max
Cl at a low angle of attack for windward work, so as not to give up too
much pointing.
But I haven't the formal analysis to be sure about the above.
>Peter Lenihan wrote:
>I've really enjoyed reading about the finer details of what makes
>for a good centerboard/leeboard. However,I wonder if what is bellow
>the waterline is all that important compared to the sails? That
>is,for our type of boats you could probably get away with using the
>kitchen table for a means of lateral resistance and that would work
>fine.....just not too sure the same could be said if one were to use
>the living room drapes for sails.
>Looking forward to some informative disscusions/exposé on sail
>shapes and drive,especially after I think about how well the Micro
>performed with her slab-side-couldn't-spell-foil-if-it-was-paid-for
>ballast keel
>
>
>Thanks!
>
--- Inbolger@yahoogroups.com, "pvanderwaart" <pvanderwaart@y...>
wrote:
Of course this only applies to racing for the most part. If I want to
gain significant seconds I start the motor:-)
Ahh... so that explains why I have been having some difficulty
understanding this.
Nels
wrote:
> It's worth significant secs/mile upwind, and good rudder shape******************************
> profile will improve handling in sharp turns quite a lot.
Of course this only applies to racing for the most part. If I want to
gain significant seconds I start the motor:-)
> For the technical, the first statement is a simplification of********************************
> something to the effect that the angle between the eye of the wind
> and the direction of the boat's progress is the sum of the arc tan
> of the l/d ratio of the sails and the arc tan of the l/d ratio of
> the foils. Something like that, at any rate.
Ahh... so that explains why I have been having some difficulty
understanding this.
Nels
> That is,for our type of boats you could probably getIt can be proved mathematically that the difference between
> away with using the kitchen table for a means of lateral
> resistance and that would work fine.....
> just not too sure the same could be said if one were to use
> the living room drapes for sails.
perfection in sailing upwind and the practically obtainable is the
linear sum of the inefficiency of the sails and the inefficiency of
the lateral plane. So they are both important. Somewhere PCB wrote
that Colin Mudie had pointed out that motorsailers with inefficient
rigs needed especially good fins.
On the other hand, PCB has also pointed out in various places that
if a fin (e.g. centerboard) is very thin, then it does not matter
much how you round or taper the edges. So, in this sense you are
right. But if you look at, say, the Norwalk Island Sharpie designs
of Bruce Kirby, you will find the foil shapes carefully designed.
It's worth significant secs/mile upwind, and good rudder shape
profile will improve handling in sharp turns quite a lot.
Peter
For the technical, the first statement is a simplification of
something to the effect that the angle between the eye of the wind
and the direction of the boat's progress is the sum of the arc tan
of the l/d ratio of the sails and the arc tan of the l/d ratio of
the foils. Something like that, at any rate.
>The short answer is "no", flat plats can generate lift, but over a very
>Therefore it seems to me that flat sided rudders would be more
>effective as they create more resistance = better turning force. Flat
>sided keels like MICRO prevent more resistance to side slipping.
limited range of angles. On the other hand a thin flat plate at 0-degrees
creates less drag than a foil. This seems to be why kayakers, who could
certainly have foil rudders if they wanted them, cling to thin aluminum.
--
Craig O'Donnell
Sinepuxent Ancestors & Boats
<http://freepages.genealogy.rootsweb.com/~fassitt/>
The Proa FAQ <http://boat-links.com/proafaq.html>
The Cheap Pages <http://www.friend.ly.net/~dadadata/>
Sailing Canoes, Polytarp Sails, Bamboo, Chinese Junks,
American Proas, the Bolger Boat Honor Roll,
Plywood Boats, Bamboo Rafts, &c.
_________________________________
-- Professor of Boatology -- Junkomologist
-- Macintosh kinda guy
Friend of Wanda the Wonder Cat, 1991-1997.
_________________________________
I've really enjoyed reading about the finer details of what makes
for a good centerboard/leeboard. However,I wonder if what is bellow
the waterline is all that important compared to the sails? That
is,for our type of boats you could probably get away with using the
kitchen table for a means of lateral resistance and that would work
fine.....just not too sure the same could be said if one were to use
the living room drapes for sails.
Looking forward to some informative disscusions/exposé on sail
shapes and drive,especially after I think about how well the Micro
performed with her slab-side-couldn't-spell-foil-if-it-was-paid-for
ballast keel :-)
Thanks!
Peter Lenihan
for a good centerboard/leeboard. However,I wonder if what is bellow
the waterline is all that important compared to the sails? That
is,for our type of boats you could probably get away with using the
kitchen table for a means of lateral resistance and that would work
fine.....just not too sure the same could be said if one were to use
the living room drapes for sails.
Looking forward to some informative disscusions/exposé on sail
shapes and drive,especially after I think about how well the Micro
performed with her slab-side-couldn't-spell-foil-if-it-was-paid-for
ballast keel :-)
Thanks!
Peter Lenihan
Thanks, Bill, for the support your summary gives to what I was trying
to say. I was beginning to wonder whether my use of the term "lift"
when referring to a keel was something I'd dreamed up, rather than
common usage.
Howard
to say. I was beginning to wonder whether my use of the term "lift"
when referring to a keel was something I'd dreamed up, rather than
common usage.
Howard
--- Inbolger@yahoogroups.com, "Bill Kreamer" <kreamer@a...> wrote:
> Asymmetrical foil sections are more efficient, reducing the drag >
that accompanies lift.
Asymmetrical foil sections are more efficient, reducing the drag that
accompanys lift. Keels are lifting foils, operating at an angle of
attack equal to the leeway angle. A symmetrical foil is a compromise -
keels are symmetrical to operate well on both tacks. If a hull can be
"reconfigured" as the boat comes about (using bilge boards, or to a
lesser extent, bilge keels), designers can use an asymmetrical section
to reduce drag.
Fast lake scows raise and lower asymmetrical bilge boards. Bilge keels
are fixed, but since they exchange positions on opposite tacks (one
producing the required lift, the other acting as ballast), some are
designed with asymmetrical sections.
Wings generally lift in one direction only and are asymmetrical for
reduced drag. Aerobatic aircraft sometimes use a compromise symmetrical
wing section that lifts "downward" as well as "up." Rudders are
symmetrical so as to lift in either direction on demand.
In general a single-element high aspect ratio foil is more efficient
than one with multiple elements. Slots and flaps are a "shifting gears"
compromise that allows for diffferent speed regimes like landing and
cruising. Displacement sailboats only have one speed regime. That said,
sailboats can't afford the weight aloft that really high aspect ratios
require so jib + main is the "pile it on" strategy.
- Bill K
-----Original Message-----
From: Nels [mailto:arvent@...]
Sent: Thursday, September 23, 2004 10:26
To:bolger@yahoogroups.com
Subject: [bolger] Re: box keel and centerboard
--- Inbolger@yahoogroups.com, "Howard Stephenson"
<stephensonhw@a...> wrote:
section. To create lift at very low speeds they require slots and
flaps and other attachements to cause even greater asymetery. I have
never seen this used in keels and see no reason why one would want
lift in a keel whose function is to prevent leeway. Are there
asymetric keel cross sections? Slender NACA foils would stall out at
the speeds our sailboats move wouldn't they?
Therefore it seems to me that flat sided rudders would be more
effective as they create more resistance = better turning force. Flat
sided keels like MICRO prevent more resistance to side slipping.
End plates on rudders prevent vorticies off the end of the rudder and
direct the water against the flat side of the rudder.
Nels
Bolger rules!!!
- no cursing, flaming, trolling, spamming, or flogging dead horses
- stay on topic, stay on thread, punctuate, no 'Ed, thanks, Fred' posts
- Pls add your comments at the TOP, SIGN your posts, and snip away
- Plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA, 01930,
Fax: (978) 282-1349
- Unsubscribe:bolger-unsubscribe@yahoogroups.com
- Open discussion:bolger_coffee_lounge-subscribe@yahoogroups.com
Yahoo! Groups Sponsor
ADVERTISEMENT
<http://us.ard.yahoo.com/SIG=129bmcpf1/M=295196.4901138.6071305.3001176/
D=groups/S=1705065791:HM/EXP=1096079207/A=2128215/R=0/SIG=10se96mf6/*htt
p://companion.yahoo.com> click here
<http://us.adserver.yahoo.com/l?M=295196.4901138.6071305.3001176/D=group
s/S=:HM/A=2128215/rand=228227281>
_____
Yahoo! Groups Links
* To visit your group on the web, go to:
http://groups.yahoo.com/group/bolger/
* To unsubscribe from this group, send an email to:
bolger-unsubscribe@yahoogroups.com
<mailto:bolger-unsubscribe@yahoogroups.com?subject=Unsubscribe>
* Your use of Yahoo! Groups is subject to the Yahoo! Terms of
Service <http://docs.yahoo.com/info/terms/> .
[Non-text portions of this message have been removed]
accompanys lift. Keels are lifting foils, operating at an angle of
attack equal to the leeway angle. A symmetrical foil is a compromise -
keels are symmetrical to operate well on both tacks. If a hull can be
"reconfigured" as the boat comes about (using bilge boards, or to a
lesser extent, bilge keels), designers can use an asymmetrical section
to reduce drag.
Fast lake scows raise and lower asymmetrical bilge boards. Bilge keels
are fixed, but since they exchange positions on opposite tacks (one
producing the required lift, the other acting as ballast), some are
designed with asymmetrical sections.
Wings generally lift in one direction only and are asymmetrical for
reduced drag. Aerobatic aircraft sometimes use a compromise symmetrical
wing section that lifts "downward" as well as "up." Rudders are
symmetrical so as to lift in either direction on demand.
In general a single-element high aspect ratio foil is more efficient
than one with multiple elements. Slots and flaps are a "shifting gears"
compromise that allows for diffferent speed regimes like landing and
cruising. Displacement sailboats only have one speed regime. That said,
sailboats can't afford the weight aloft that really high aspect ratios
require so jib + main is the "pile it on" strategy.
- Bill K
-----Original Message-----
From: Nels [mailto:arvent@...]
Sent: Thursday, September 23, 2004 10:26
To:bolger@yahoogroups.com
Subject: [bolger] Re: box keel and centerboard
--- Inbolger@yahoogroups.com, "Howard Stephenson"
<stephensonhw@a...> wrote:
> Wings and keels in sailing boats are both there to produce a forcecalled "lift",
> roughly perpendicular to their surface, vertically in the case of a
> wing and horizontally in the case of a fin. It's often
> whether vertically in the air, or horizontally in the water. Ofhits
> course keels often have other functions too -- as do aircraft wings.
>
> Their close similarity in design can be seen easily by Googling on
> something like <fin NACA section> and see how many boat-related
> you will get. NACA = National Advisory Committee of Aeronautics.Aircraft wings create lift by being curved and asymetrical in cross-
>
> Howard
>
section. To create lift at very low speeds they require slots and
flaps and other attachements to cause even greater asymetery. I have
never seen this used in keels and see no reason why one would want
lift in a keel whose function is to prevent leeway. Are there
asymetric keel cross sections? Slender NACA foils would stall out at
the speeds our sailboats move wouldn't they?
Therefore it seems to me that flat sided rudders would be more
effective as they create more resistance = better turning force. Flat
sided keels like MICRO prevent more resistance to side slipping.
End plates on rudders prevent vorticies off the end of the rudder and
direct the water against the flat side of the rudder.
Nels
Bolger rules!!!
- no cursing, flaming, trolling, spamming, or flogging dead horses
- stay on topic, stay on thread, punctuate, no 'Ed, thanks, Fred' posts
- Pls add your comments at the TOP, SIGN your posts, and snip away
- Plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA, 01930,
Fax: (978) 282-1349
- Unsubscribe:bolger-unsubscribe@yahoogroups.com
- Open discussion:bolger_coffee_lounge-subscribe@yahoogroups.com
Yahoo! Groups Sponsor
ADVERTISEMENT
<http://us.ard.yahoo.com/SIG=129bmcpf1/M=295196.4901138.6071305.3001176/
D=groups/S=1705065791:HM/EXP=1096079207/A=2128215/R=0/SIG=10se96mf6/*htt
p://companion.yahoo.com> click here
<http://us.adserver.yahoo.com/l?M=295196.4901138.6071305.3001176/D=group
s/S=:HM/A=2128215/rand=228227281>
_____
Yahoo! Groups Links
* To visit your group on the web, go to:
http://groups.yahoo.com/group/bolger/
* To unsubscribe from this group, send an email to:
bolger-unsubscribe@yahoogroups.com
<mailto:bolger-unsubscribe@yahoogroups.com?subject=Unsubscribe>
* Your use of Yahoo! Groups is subject to the Yahoo! Terms of
Service <http://docs.yahoo.com/info/terms/> .
[Non-text portions of this message have been removed]
Assymetry in keels is so effective that it is outlawed in some
classes. By this I mean that it is not permitted to have a separate
rudder and another rudder attached to the aft edge of the keel, to
act as a flap or aileron.
It's obviously not possible to design fixed assymetry into a
centreline keel because the boat would sail better on one tack than
on the other. Bilgekeels or twin keels sometimes are asymmetrical,
with varying degrees of success. Leeboards are sometimes shaped (with
more curvature on one surface than the other) and/or mounted
asymmetrically, at a small angle to the centreline. Catamarans can
and sometimes do have two asymmetrical fins.
If you think about the old-fashioned rudder attached to the fin keel -
- still used on most cruising keelboats -- it is just like a wing
with a flap or aileron on it. In fact, Bolger and others have said
many times that sailboats go to windward better when they carry a
little weather helm, with the rudder not trailing directly behind the
keel.
If you study airplanes designed for aerobatics, you will find that
their wing sections are in fact symmetrical. They are like this so
the plane can fly upside-down just as well as it can fly the right
way up. The wing develops lift by flying at an angle (the angle of
attack) to the oncoming air -- just as a symmetrical keel does.
The "lift" we are interested in producing with a keel or fin or
centreboard or leeboard is actually a side force. The fin is like a
wing on its side. The fact that it is often called lift shows the
similarity between wings and fins. But it has nothing to do with
trying to lift the boat out of the water.
Slender NACA foils sections are often used on sailboats, as a quick
Google search will show you. To be competitive in some of the model
classes e.g. US1metre, it's necessary to have an exceedingly thin
fin. Model boats move very slowly when compared with airplanes, but
the fins are in a much denser medium than air.
Howard
classes. By this I mean that it is not permitted to have a separate
rudder and another rudder attached to the aft edge of the keel, to
act as a flap or aileron.
It's obviously not possible to design fixed assymetry into a
centreline keel because the boat would sail better on one tack than
on the other. Bilgekeels or twin keels sometimes are asymmetrical,
with varying degrees of success. Leeboards are sometimes shaped (with
more curvature on one surface than the other) and/or mounted
asymmetrically, at a small angle to the centreline. Catamarans can
and sometimes do have two asymmetrical fins.
If you think about the old-fashioned rudder attached to the fin keel -
- still used on most cruising keelboats -- it is just like a wing
with a flap or aileron on it. In fact, Bolger and others have said
many times that sailboats go to windward better when they carry a
little weather helm, with the rudder not trailing directly behind the
keel.
If you study airplanes designed for aerobatics, you will find that
their wing sections are in fact symmetrical. They are like this so
the plane can fly upside-down just as well as it can fly the right
way up. The wing develops lift by flying at an angle (the angle of
attack) to the oncoming air -- just as a symmetrical keel does.
The "lift" we are interested in producing with a keel or fin or
centreboard or leeboard is actually a side force. The fin is like a
wing on its side. The fact that it is often called lift shows the
similarity between wings and fins. But it has nothing to do with
trying to lift the boat out of the water.
Slender NACA foils sections are often used on sailboats, as a quick
Google search will show you. To be competitive in some of the model
classes e.g. US1metre, it's necessary to have an exceedingly thin
fin. Model boats move very slowly when compared with airplanes, but
the fins are in a much denser medium than air.
Howard
--- Inbolger@yahoogroups.com, "Nels" <arvent@h...> wrote:
> Aircraft wings create lift by being curved and asymetrical in cross-
> section. To create lift at very low speeds they require slots and
> flaps and other attachements to cause even greater asymetery. I
have
> never seen this used in keels and see no reason why one would want
> lift in a keel whose function is to prevent leeway. Are there
> asymetric keel cross sections? Slender NACA foils would stall out
at
> the speeds our sailboats move wouldn't they?
>
> Therefore it seems to me that flat sided rudders would be more
> effective as they create more resistance = better turning force.
Flat
> sided keels like MICRO prevent more resistance to side slipping.
>
> End plates on rudders prevent vorticies off the end of the rudder
and
> direct the water against the flat side of the rudder.
>
> Nels
--- Inbolger@yahoogroups.com, fountainb@s... wrote:
underside. This would create lift in my view, and therefore less
wetted surface on the hull as the boat accelerates. Also it would
assist in keeping the boat upright, presenting more sail to the wind.
The keel sides seem quite flat with some taper along the front edge
and a more tapered area at the aft edge. The rudders seem completely
flat like boards. (These observations from the Ostar Racer mods in
the files folder called "Foils: boards, rudders keels)
Nels
> Nels wrote:The Bolger swing wing has a completely flat top and a curved
> > Are there asymetric keel cross sections?
>
> Perhaps asymetric dagger boards might make
> sense for a catamaran?
>
underside. This would create lift in my view, and therefore less
wetted surface on the hull as the boat accelerates. Also it would
assist in keeping the boat upright, presenting more sail to the wind.
The keel sides seem quite flat with some taper along the front edge
and a more tapered area at the aft edge. The rudders seem completely
flat like boards. (These observations from the Ostar Racer mods in
the files folder called "Foils: boards, rudders keels)
Nels
Nels wrote:
sense for a catamaran?
Bruce Fountain
Systems Engineer
Union Switch & Signal
Perth, Western Australia
[Non-text portions of this message have been removed]
> Are there asymetric keel cross sections?Perhaps asymetric dagger boards might make
sense for a catamaran?
Bruce Fountain
Systems Engineer
Union Switch & Signal
Perth, Western Australia
[Non-text portions of this message have been removed]
--- Inbolger@yahoogroups.com, "Howard Stephenson"
<stephensonhw@a...> wrote:
section. To create lift at very low speeds they require slots and
flaps and other attachements to cause even greater asymetery. I have
never seen this used in keels and see no reason why one would want
lift in a keel whose function is to prevent leeway. Are there
asymetric keel cross sections? Slender NACA foils would stall out at
the speeds our sailboats move wouldn't they?
Therefore it seems to me that flat sided rudders would be more
effective as they create more resistance = better turning force. Flat
sided keels like MICRO prevent more resistance to side slipping.
End plates on rudders prevent vorticies off the end of the rudder and
direct the water against the flat side of the rudder.
Nels
<stephensonhw@a...> wrote:
> Wings and keels in sailing boats are both there to produce a forcecalled "lift",
> roughly perpendicular to their surface, vertically in the case of a
> wing and horizontally in the case of a fin. It's often
> whether vertically in the air, or horizontally in the water. Ofhits
> course keels often have other functions too -- as do aircraft wings.
>
> Their close similarity in design can be seen easily by Googling on
> something like <fin NACA section> and see how many boat-related
> you will get. NACA = National Advisory Committee of Aeronautics.Aircraft wings create lift by being curved and asymetrical in cross-
>
> Howard
>
section. To create lift at very low speeds they require slots and
flaps and other attachements to cause even greater asymetery. I have
never seen this used in keels and see no reason why one would want
lift in a keel whose function is to prevent leeway. Are there
asymetric keel cross sections? Slender NACA foils would stall out at
the speeds our sailboats move wouldn't they?
Therefore it seems to me that flat sided rudders would be more
effective as they create more resistance = better turning force. Flat
sided keels like MICRO prevent more resistance to side slipping.
End plates on rudders prevent vorticies off the end of the rudder and
direct the water against the flat side of the rudder.
Nels
Hello from a Bolger newbie,
I've been, shall we say, increasingly drawn to shoal draft designs and after
seeing BirdWatcher in WB I found this list. This VERY active list.
It's been very interesting so far, an informative read and Would love to
hear more on BW.
Cheers
Darren
A free foil program.
http://www.compufoil.com/
Easy to use NACA numbers to create and scale foils.
_____
From: Howard Stephenson [mailto:stephensonhw@...]
Sent: Thursday, September 23, 2004 6:22 PM
To:bolger@yahoogroups.com
Subject: [bolger] Re: box keel and centerboard
Wings and keels in sailing boats are both there to produce a force
roughly perpendicular to their surface, vertically in the case of a
wing and horizontally in the case of a fin. It's often called "lift",
whether vertically in the air, or horizontally in the water. Of
course keels often have other functions too -- as do aircraft wings.
Their close similarity in design can be seen easily by Googling on
something like <fin NACA section> and see how many boat-related hits
you will get. NACA = National Advisory Committee of Aeronautics.
Howard
I've been, shall we say, increasingly drawn to shoal draft designs and after
seeing BirdWatcher in WB I found this list. This VERY active list.
It's been very interesting so far, an informative read and Would love to
hear more on BW.
Cheers
Darren
A free foil program.
http://www.compufoil.com/
Easy to use NACA numbers to create and scale foils.
_____
From: Howard Stephenson [mailto:stephensonhw@...]
Sent: Thursday, September 23, 2004 6:22 PM
To:bolger@yahoogroups.com
Subject: [bolger] Re: box keel and centerboard
Wings and keels in sailing boats are both there to produce a force
roughly perpendicular to their surface, vertically in the case of a
wing and horizontally in the case of a fin. It's often called "lift",
whether vertically in the air, or horizontally in the water. Of
course keels often have other functions too -- as do aircraft wings.
Their close similarity in design can be seen easily by Googling on
something like <fin NACA section> and see how many boat-related hits
you will get. NACA = National Advisory Committee of Aeronautics.
Howard
--- Inbolger@yahoogroups.com, "Nels" <arvent@h...> wrote:
> --- Inbolger@yahoogroups.com, Lincoln Ross <lincolnr@r...> wrote:
> Mr. Bolger also cautions about comparing centerboards AND sails to
> airplane wings. Their functions are in no way similar, unless used
> horizontally like the swing-wing keel of the I60, or the end plates
> on some of the rudders.
Bolger rules!!!
- no cursing, flaming, trolling, spamming, or flogging dead horses
- stay on topic, stay on thread, punctuate, no 'Ed, thanks, Fred' posts
- Pls add your comments at the TOP, SIGN your posts, and snip away
- Plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA, 01930, Fax:
(978) 282-1349
- Unsubscribe:bolger-unsubscribe@yahoogroups.com
- Open discussion:bolger_coffee_lounge-subscribe@yahoogroups.com
Yahoo! Groups Sponsor
ADVERTISEMENT
<http://us.ard.yahoo.com/SIG=129l4rec9/M=295196.4901138.6071305.3001176/D=gr
oups/S=1705065791:HM/EXP=1096075353/A=2128215/R=0/SIG=10se96mf6/*http:/compa
nion.yahoo.com> click here
<http://us.adserver.yahoo.com/l?M=295196.4901138.6071305.3001176/D=groups/S=
:HM/A=2128215/rand=321752600>
_____
Yahoo! Groups Links
* To visit your group on the web, go to:
http://groups.yahoo.com/group/bolger/
* To unsubscribe from this group, send an email to:
bolger-unsubscribe@yahoogroups.com
<mailto:bolger-unsubscribe@yahoogroups.com?subject=Unsubscribe>
* Your use of Yahoo! Groups is subject to the Yahoo!
<http://docs.yahoo.com/info/terms/> Terms of Service.
[Non-text portions of this message have been removed]
Wings and keels in sailing boats are both there to produce a force
roughly perpendicular to their surface, vertically in the case of a
wing and horizontally in the case of a fin. It's often called "lift",
whether vertically in the air, or horizontally in the water. Of
course keels often have other functions too -- as do aircraft wings.
Their close similarity in design can be seen easily by Googling on
something like <fin NACA section> and see how many boat-related hits
you will get. NACA = National Advisory Committee of Aeronautics.
Howard
roughly perpendicular to their surface, vertically in the case of a
wing and horizontally in the case of a fin. It's often called "lift",
whether vertically in the air, or horizontally in the water. Of
course keels often have other functions too -- as do aircraft wings.
Their close similarity in design can be seen easily by Googling on
something like <fin NACA section> and see how many boat-related hits
you will get. NACA = National Advisory Committee of Aeronautics.
Howard
--- Inbolger@yahoogroups.com, "Nels" <arvent@h...> wrote:
> --- Inbolger@yahoogroups.com, Lincoln Ross <lincolnr@r...> wrote:
> Mr. Bolger also cautions about comparing centerboards AND sails to
> airplane wings. Their functions are in no way similar, unless used
> horizontally like the swing-wing keel of the I60, or the end plates
> on some of the rudders.
--- Inbolger@yahoogroups.com, Lincoln Ross <lincolnr@r...> wrote:
HASLER, FIJI, ALERT. An original "box keel" example is MICRO
according to PCB - with the keel box extending out to the bilges and
a low aspect fin added:-)
Of course centerboards can be either low or high aspect. I have
always been intrigued by the 25 foot lapstrake CHEBACCO which has a
shallow bulb keel, and a 3/8" thick 60 pound flat cut centerboard.
Mr. Bolger also cautions about comparing centerboards AND sails to
airplane wings. Their functions are in no way similar, unless used
horizontally like the swing-wing keel of the I60, or the end plates
on some of the rudders.
So another question. Is the JOCHENS SCHOONER the last Bolger design
to utilize leeboards?
To me it is curious as he spoke so highly of them for so long.
Perhaps off-center boards and twin bilgeboards like on the AS series
proved superior in the final analysis?
Cheers, Nels
> A box keel is low aspect ratio, and a centerboard is high aspectratio.
> If there are both, the centerboard will be working a lot harderthan the
> box keel up until it stalls. High aspect ratio surfaces reach ahigher
> lift coefficient for any given angle of attack, although notnecessarily
> a higher maximum lift coefficient. So they won't really worktogether
> very well.The type of keel combination I am referring to is exemplified by COL.
HASLER, FIJI, ALERT. An original "box keel" example is MICRO
according to PCB - with the keel box extending out to the bilges and
a low aspect fin added:-)
Of course centerboards can be either low or high aspect. I have
always been intrigued by the 25 foot lapstrake CHEBACCO which has a
shallow bulb keel, and a 3/8" thick 60 pound flat cut centerboard.
Mr. Bolger also cautions about comparing centerboards AND sails to
airplane wings. Their functions are in no way similar, unless used
horizontally like the swing-wing keel of the I60, or the end plates
on some of the rudders.
So another question. Is the JOCHENS SCHOONER the last Bolger design
to utilize leeboards?
To me it is curious as he spoke so highly of them for so long.
Perhaps off-center boards and twin bilgeboards like on the AS series
proved superior in the final analysis?
Cheers, Nels
A box keel is low aspect ratio, and a centerboard is high aspect ratio.
If there are both, the centerboard will be working a lot harder than the
box keel up until it stalls. High aspect ratio surfaces reach a higher
lift coefficient for any given angle of attack, although not necessarily
a higher maximum lift coefficient. So they won't really work together
very well.
If there are both, the centerboard will be working a lot harder than the
box keel up until it stalls. High aspect ratio surfaces reach a higher
lift coefficient for any given angle of attack, although not necessarily
a higher maximum lift coefficient. So they won't really work together
very well.