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Physics of wing keels

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Gloss
Master Marine Consultant

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USA
1916 Posts

Initially Posted - 12/03/2002 : 19:51:58

Here is a question for you engineering and marine architecture types.

What are some of the physics and dynamic forces involved in a moving and/or heeling wing keel? Do the wings impart any other stability, other than it's sheer weight, in righting, or slip resistance.

I guesse I have too much time on my hands to wonder these things.

Yes grasshopper, you do.

thanks
Frank Gloss
fgloss@knology.net

Frank

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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 12/05/2002 : 19:26:50

Frank... I think the simple answer is that as the boat heels, the standard keel goes from vertical (maximum lateral resistance) toward horizontal (no lateral resistance). Add a wing, and it starts adding lateral resistance as its surface moves from horizontal toward vertical. The wing also adds a little depth to a shoal draft keel as the boat heels. There are also discussions about enhancing "laminar flows" (?) that may be significant on AC boats, but probably a stretch on our boats with their fat keels and low speeds.

BTW, high-performance wing keels often have the wings angled down from the fin--I suspect so that the leeward wing becomes close to vertical at normal-to-high heel angles.

Dave Bristle - 1985 C-25 #5032 SR-FK-Dinette-Honda "Passage" in SW CT

Edited by - Dave Bristle on 12/05/2002 19:30:52

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Arlyn Stewart
Master Marine Consultant

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2984 Posts

Response Posted - 12/06/2002 : 12:11:31

To add slightly to Daves good explanation... The wing of course was an invention to curb the loss of laminar flow (especially during heeling)but that was on deep fin keels. The wing on a shoal draft is a significant adaptation and of course allows weight volume fairly low without too large of a structure inducing major drag.

The "incidence" (angle at which the foil is presented) can also be a factor. A hydrofoil boat has wings with positive "incidence" to lift the hull out of the water and plane on the wing. A sailboat might be designed with a slightly negative "incidence" wing that lifts downward and therefore to weather when when heeling, but this is only effective on a boat which can be sailed heeled without suffering balance shifts.

IMHO Shoal wings are a temporary keel in the evolution. They were an answer to the problems of heavy swing keels rather than better performers. There is a better keel if it can be made to work in producing our size boats.... that is the twin... which can be built with asymetric foils favorable to lifting windward to the tack for which the keel is burried. The burried keel then has maximum lateral resistance and most lift to weather.

If a coastal cruiser such as the c25 and c250 could be designed with less of a balance shift problem when heeling and twin keels... and be easily trailered... I could get real excited. er...oh yeah... affordable too.

<img src="http://www.cox-internet.com/arlynstewart/images/helming.jpg" border=0>
Arlyn C-250 W/B #224
R&R N/E Texas and Great Lakes

[url="http://www.cox-internet.com/arlynstewart/"]Arlyn's C250 Mods n Cruisin Stories[/url]

Edited by - arlyn stewart on 12/06/2002 12:13:55

Edited by - arlyn stewart on 12/06/2002 12:17:02

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Gloss
Master Marine Consultant

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1916 Posts

Response Posted - 12/06/2002 : 14:42:14

Affordable?

Now there's a concept

Frank

Frank

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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 12/06/2002 : 15:53:13

Arlyn... There's one of those things in our storage yard--a "bilge-keeler." It sits on the two keels with only a bow stand. I suspect it gives up some righting moment and/or adds some drag because the keels have to have more surface and weight when they're on both sides of the centerline--just as water ballast spread across the hull requires more weight than internal lead closer to the centerline to get the same righting moment.

Wait--you said asymetric... There are LOTS of those around--they're call Hobies! You sail on one "keel" or the other.

Dave Bristle - 1985 C-25 #5032 SR-FK-Dinette-Honda "Passage" in SW CT

Edited by - dave bristle on 12/06/2002 16:03:09

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Steve Milby
Past Commodore

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USA
5932 Posts

Response Posted - 12/06/2002 : 16:32:02

The wing keel was first introduced in an America's Cup boat. Its original purpose was to beat the 12 meter design rule by using a shallower keel, and still getting enough weight down low to keep the boat on her feet. They quickly became popular with buyers of small boats, because they permit shallow draft boats that sail reasonably well, and they enable the boat builders to eliminate troublesome retractable keel mechanisms. Generally they're not thought to be quite as efficient as a fin keel, especially going to weather, but they still provide very good performance.

Twin keel boats are generally thought to provide a steady motion in a seaway, and, if they are left aground where there is a wide tidal range, they will stand on their own two keels, but the fact that they have such a large wetted surface makes them <u>agonizingly</u> slow.

Steve Milby "Captiva Wind" C-25 T/FK #2554

Edited by - on

ronrryan
Admiral

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USA
561 Posts

Response Posted - 12/06/2002 : 20:31:34

Two points: one, Phil Bolger has added "end plates" as wings to rudders for years, to keep the flow of water from "dumping" off the bottom of the rudder and to give greater efficiency with a shallower draft, I am not knowledgeable enough to describe the hydrodynamics involved, but if Bolger is a believer, then so am I, Two, have owned twin keel boats, and many years ago the British "Jaguar" line of Catalinas was offered with a twin keel variation. The review of the 27 model in an old Yachting Monthly stated there was very little difference in performance between the fin and twin, which struck me as rather unusual, and a designing triumph, if true, ron srsk 1981 Orion #2343 SW FLA

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oldsalt
Admiral

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USA
578 Posts

Response Posted - 12/06/2002 : 22:05:55

The winged keel was introduced as a 12 meter rule beating measure.

The 12 meter formula provided penalties for parameters such as waterline length, sail area, lighter displacement and draft.

If a designer increased any of these parameters (or lessend displacement), he took penalties in other areas of his choosing.

The original winged keel used by Australia ll allowed for decreased "measured" draft as well as increased righting moment due to the extra weight that the wings provided.

As well as an end plate effect.

The most important feature of the wings was that the rule considered the draft measurement while the vessel was at rest.

When heeled, the wing provided additional draft which was not measured and therefore not penalized.

There is no magic to wings as they are not as efficient as deeper, well designed foils since they exhibit more drag due to extra wetted surface, but they do make for efficient shoal draft keels.

One of the problems with fin keels on cruising boats is the way they distribute the load of a vessel in the event of a grounding since they cause extra stress on the keel bolts as well as the hull.

Regards: Oldsalt

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tinob
Master Marine Consultant

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1883 Posts

Response Posted - 12/07/2002 : 09:25:01

PHEW!,

I've often been asked to describe the difference between the old swing and the retrofitted wing of my boat. Initially I hadn't a clew spending most of my time being thankful that I finally had a sailboat. So I spent some time of each sail considering the difference (if any) between the two. I thought at first that the wing leaving the lagoon at slow speed was light on tracking and didn't track well until speed increased. As I used the wing more ,prompted by your questions, I thought that the major difference became apparent when the boat heeled but the swing was long gone by then and easily forgotten.

It is interesting to read each of the critiques expressed that confirm what I thought the wing was trying to tell me, "if ya want me ta work for ya ya gotta lay me down".

Thanks Val on "CALISTA" # 3936

Val Bisagni

Edited by - on

Gloss
Master Marine Consultant

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USA
1916 Posts

Response Posted - 12/07/2002 : 09:48:48

End Plate Effect

Is this the effect of catching flow off the end of the keel and redirecting it? Kind of like the winglets on my Gulfstream jet? I assume that the end plate effect is a dynamic, rather than a static process.
Does this end plate effect cause the keel to want to right? Or does it make the keel to want to hunker down lower in the water, and thus cause more righting moment indirectly?
I appreciate the discussions so far. You folks are convincing me more and more to buy a wing, and not a swing.
Should be safer when I sail to the Dry tortugas and Marquesas. Of course I also have to trailer it. Thats why I'm not getting a fin.
Thanks again
Frank Gloss
C22 owner, soon to be C25 owner--you can never have too many boats. I also have two sailboards and a whitewater kayak.

Frank

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oldsalt
Admiral

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578 Posts

Response Posted - 12/07/2002 : 14:12:59

The end plate effect reduces turbulence at the point where the water flow separates from the foil; the bottom of the keel.

Less turbulence = less drag and more boatspeed.

Winglet on the wingtips are there for the same purpose.

Edited by - oldsalt on 12/07/2002 14:14:50

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