Wing keel vs fin keel

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Hmmm. Catalina's version of this is closer to my understanding of the reason for vertical winglets at the wingtips of modern aircraft.

If I may quote to you from an abstract in an article in the International Journal of Naval Architecture and Ocean Engineering

"The endplate causes a blockage effect on the flow, and an additional viscous effect especially near the endplate. These combined effects of the endplate significantly reduce the magnitudes of the velocities under the lower surface of the wing, thereby enhancing aerodynamic performance in terms of the force coefficients. The maximum lift-to-drag ratio of a wing with an endplate is increased 46% compared to that of wing without an endplate at the lowest clearance. The tip vortex of a wing-with-endplate (WWE) moved laterally to a greater extent than that of a wing-without-endplate (WOE). This causes a decrease in the induced drag, resulting in a reduction in the total drag."
I'm grateful for your technical explanation of what I'd understood to be the case. TBH I was a little surprised that the reason was "fitting into terminal gates", given that they fit tabs to aircraft with smaller wingspans than older planes like 747's which don't have them but which still fit the gates. They could just make the wings longer!
 

DJE

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I'm grateful for your technical explanation of what I'd understood to be the case. TBH I was a little surprised that the reason was "fitting into terminal gates", given that they fit tabs to aircraft with smaller wingspans than older planes like 747's which don't have them but which still fit the gates. They could just make the wings longer!
Terminal gates vary in size. Smaller planes are designed to fit smaller gates.
Airplane Design Group (ADG) - SKYbrary Aviation Safety
 

TLouth7

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Hmmm. Catalina's version of this is closer to my understanding of the reason for vertical winglets at the wingtips of modern aircraft.

If I may quote to you from an abstract in an article in the International Journal of Naval Architecture and Ocean Engineering

"The endplate causes a blockage effect on the flow, and an additional viscous effect especially near the endplate. These combined effects of the endplate significantly reduce the magnitudes of the velocities under the lower surface of the wing, thereby enhancing aerodynamic performance in terms of the force coefficients. The maximum lift-to-drag ratio of a wing with an endplate is increased 46% compared to that of wing without an endplate at the lowest clearance. The tip vortex of a wing-with-endplate (WWE) moved laterally to a greater extent than that of a wing-without-endplate (WOE). This causes a decrease in the induced drag, resulting in a reduction in the total drag."

That is true as compared to wings of the same length. In the same way a winged keel should have lower drag than a fin keel of the same depth. The purpose of winglets or endplates is to increase the effective aspect ratio of a foil (this is what your quote is saying in complex language). Increasing the span of the foil would achieve the same thing with less drag because corners always introduce interference drag.

So wing keels are a good way of mitigating the disadvantage of shallower keels, but can never quite achieve the same lift-to-drag ratio as a fin keel of greater depth.

PS smaller airport terminal gates are cheaper to stop at. Even cheaper is to park on the tarmac and get a bus to the terminal.
 

flaming

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The other thing that hasn't been mentioned is that you can't really consider the keel in isolation from the hull shape.

For example if you have a narrow hull with little in the way of form stability then the keel has a much greater job to do in terms of being able to stand up to the sail plan. This lead, in racing terms at least, to a trend towards deep skinny kin keels with big bulbs hanging off the end. This setup tended to be very fast upwind, and downwind in light to medium winds, but was overall too heavy and narrow to plane. The bulb is also a source of drag, and the skinny keel makes the boat tweakier and harder to helm.
With the advent of fatter hull forms for "normal" racing by the likes of pogo and JPK etc, the trend now is towards slab fin keels that wouldn't have looked out of place on an old IOR ton class yacht. The advantages here are that the keel shape makes the boat easier to helm (especially important for shorthanded boats driven mostly by autopilot) and actually have less resistance downwind than the fin and bulb.
The trade off is a small loss in righting moment, but the idea being that you more than get that back from the hull shape.

Wing keels are somewhere in between. If your hull is narrow and your boat is heavy then they are more likely to be an overall benefit than if your hull is wide and your boat light.
 

anoccasionalyachtsman

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I'm grateful for your technical explanation of what I'd understood to be the case. TBH I was a little surprised that the reason was "fitting into terminal gates", given that they fit tabs to aircraft with smaller wingspans than older planes like 747's which don't have them but which still fit the gates. They could just make the wings longer!
I think he may be confusing winglets/sharklets with the folding tips on the 777 Max.
 

Graham376

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The purpose of winglets or endplates is to increase the effective aspect ratio of a foil (this is what your quote is saying in complex language). Increasing the span of the foil would achieve the same thing with less drag because corners always introduce interference drag.

The winglets are there to reduce induced drag by minimising the wingtip vortices created when the high and low pressure across the wing meet at the tip. They are also less speed limiting than increasing the span. My last glider had a higher vne and max manoeuvre speed with its vertical winglets than with the optional wing extensions.
 

Laminar Flow

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In conclusion and in reference to the Delft study the difference in performance between a deep keel and a wingkeel with only 57% of the span of it's deeper competitor is 1.26% or three minutes in 2.37 hours over an Olympic course (66% to windward)

This slight disadvantage accounts for lighter wind speeds only (15kts). In higher wind speeds (25kts) the difference is virtually undetectable.

In racing terms, three minutes late means you still don't get to join the party.

In my world of cruising there is only one winner here: the wingkeel.
Near identical performance with a draft of three feet less (re study). Add to this improved directional stability and there really isn't a choice.
 

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If you look at the wings on an F1 car, they have had end plates for many years. Never heard of anyone putting Gurney Tabs on a keel though....
 

geem

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In conclusion and in reference to the Delft study the difference in performance between a deep keel and a wingkeel with only 57% of the span of it's deeper competitor is 1.26% or three minutes in 2.37 hours over an Olympic course (66% to windward)

This slight disadvantage accounts for lighter wind speeds only (15kts). In higher wind speeds (25kts) the difference is virtually undetectable.

In racing terms, three minutes late means you still don't get to join the party.

In my world of cruising there is only one winner here: the wingkeel.
Near identical performance with a draft of three feet less (re study). Add to this improved directional stability and there really isn't a choice.
Does the Delft study consider wave action when going to windward in 25kts of wind. In open sea you would expect waves of 2.5m. The grip a deep keel gives beating in these conditions is significant. In these conditions we can tack through 90deg. I would never say it was pleasant but we do it. I would be surprised if any shorter keel, even with wings would be as efficient in these conditions
 
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Does the Delft study consider wave action when going to windward in 25kts of wind. In open sea you would expect waves of 2.5m. The grip a deep keel gives beating in these conditions is significant. In these conditions we can tack through 90deg. I would never say it was pleasant but we do it. I would be surprised if any shorter keel, even with wings would be as efficient in these conditions
"I would never say it was pleasant but we do it. "

It isn't and though I've done it through necessity I never choose to. Having a keel that will do that a bit better while being slower and less convenient in the other 99.9% of sailing I do doesn't seem to make a lot of sense to me.
 

flaming

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In conclusion and in reference to the Delft study the difference in performance between a deep keel and a wingkeel with only 57% of the span of it's deeper competitor is 1.26% or three minutes in 2.37 hours over an Olympic course (66% to windward)

This slight disadvantage accounts for lighter wind speeds only (15kts). In higher wind speeds (25kts) the difference is virtually undetectable.

In racing terms, three minutes late means you still don't get to join the party.

In my world of cruising there is only one winner here: the wingkeel.
Near identical performance with a draft of three feet less (re study). Add to this improved directional stability and there really isn't a choice.
You do forget the other variable - price. Normally the wing keel option is considerably more expensive.

Also worth mentioning that those numbers are valid for that hull shape. Change the hull shape to either a much narrower one, or a much wider "open" style one and you may well see a different outcome.

Wings on keels briefly came back into vogue in racing circles in the mid 2000s, with high aspect ratio wings being added to bulb keels, most notably by Team Origin's ill fated TP52 campaign. They were promptly banned in that class as an unnecessary complication that was going to cost a lot in terms of testing and development and not add much in terms of speed and racing.
Obviously more recently classes have been separating the foils from the keels with DSS or IMOCA style foils.

I keep wondering if the addition of a foil like a DSS or even Figaro Style, to a lift keel design could be quite an effective cruising solution to give shallow draft, dampened motion and better performance.
Ups the cost and complication of course but....
 
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Robin

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We had a winged keel on a Benny Oceanis 36 CC in the USA, It was a French built one imported by original owner not a yank build. It sailed pretty good and the shallow draft made it very good for the skinny waters of the 'ditch' aka ICW. We installed a new UK made triradial in mast main and a triradial roller genoa both in Hydranet. Never sailed a normal fin version or even close to one to make comparisons. It was a PITA to antifoul, resolved simply by paying somebody else to do it in the Florida heat.
 

Sharky34

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In conclusion and in reference to the Delft study the difference in performance between a deep keel and a wingkeel with only 57% of the span of it's deeper competitor is 1.26% or three minutes in 2.37 hours over an Olympic course (66% to windward)

This slight disadvantage accounts for lighter wind speeds only (15kts). In higher wind speeds (25kts) the difference is virtually undetectable.

In racing terms, three minutes late means you still don't get to join the party.

In my world of cruising there is only one winner here: the wingkeel.
Near identical performance with a draft of three feet less (re study). Add to this improved directional stability and there really isn't a choice.
"Improved directional stability"?
 

Skellum

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If looking to buy a boat for sailing in an area where draft is often an issue - eg Suffolk / Essex , but don't want to go for twin keels, which wing keeled boats do people rate?
 

Robin

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Not that my moniker gives any clues.
We were seriously considering buying a new c36 at Soton Boatshow one year, dealer had one at a favourable price due to exchange rate. However we had to twist his arm hard to viewthe underneath that was hidden behind display boarding. When we did we saw the shallow wing keel but with the deep version rudder which was a NO NO NO!! The dealer tried to persuade us to accept him having it shortened at which stage we walked, nay ran! we went used and bought a Jeanneau Sun Lgende 41 modded for long distance live aboard cruising, best boat we have ever owned, but with 2.1 metre draft not for shallow waters.
 
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We were seriously considering buying a new c36 at Soton Boatshow one year, dealer had one at a favourable price due to exchange rate. However we had to twist his arm hard to viewthe underneath that was hidden behind display boarding. When we did we saw the shallow wing keel but with the deep version rudder which was a NO NO NO!! The dealer tried to persuade us to accept him having it shortened at which stage we walked, nay ran! we went used and bought a Jeanneau Sun Lgende 41 modded for long distance live aboard cruising, best boat we have ever owned, but with 2.1 metre draft not for shallow waters.
It's a fair point. I shortened my rudder by about 3" to match the keel without any discernible difference to the steering. Catalina did themselves no favours economising on one rudder design rather than two, which is a pity given the many good points about the boat.
 

Laminar Flow

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Does the Delft study consider wave action when going to windward in 25kts of wind. In open sea you would expect waves of 2.5m. The grip a deep keel gives beating in these conditions is significant. In these conditions we can tack through 90deg. I would never say it was pleasant but we do it. I would be surprised if any shorter keel, even with wings would be as efficient in these conditions
To be clear; I do not know if the Delft study specifically investigated behavior in waves. I do know that resistance caused by waves is commonly entered when assessing overall resistance of a boat's design.
What I can tell is that the study was conducted for a 63' boat and it can reasonably be assumed that the canoe body on this alone would have a depth of 90 to 100cm. So even with a shallow keel, overall draft would have been around 2.35m.
I doubt that even with this "shallow" a draft a 63 footer would have trouble going to weather in 25kts.

From some of your previous posts I understand that your boat is fairly large - 48'? and size does matter in terms of stability.

Grip is a rather simplistic way of way of explaining the effectiveness of a keel. Lift is what counts. The proximity of the hull to the keel acts as an endplate and doubles the effective span of the keel. However that still leaves us with the tip where the pressure side leaks to the low pressure side, causing energy sapping vortices, referred to as induced drag, and rendering a large portion of the keel ineffective. The answer to this was to simply make the keel deeper and to keep the wetted area in check, to shorten the cord of the profile. It also has the bonus of cutting down the area of induced drag. As a result you end up with those skinny deep keels Flaming mentioned. Profiles with a short cord are much more prone to stalling, however, especially in turbulent conditions (the perhaps only and single most important advantage of a long keel).
In comes the wingkeel and adds endplates to the bottom as well and consequently you, once again, increase the effective span. Unlike a passenger aircraft that tends to (and should) fly right way up only, a keel has to generate lift on alternate sides and so you end up with two winglets, one of which is just along for the ride and contributes only to wetted area.
To compare, Delft also tested a long shallow fin which was worse than the wingkeel by a factor of four. total draft still 2.4m.

The improved directional stability was an observation made by Sadler yachts who tested various keel forms on a series of their boats.
 

Robin

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It's a fair point. I shortened my rudder by about 3" to match the keel without any discernible difference to the steering. Catalina did themselves no favours economising on one rudder design rather than two, which is a pity given the many good points about the boat.

The one on show had a rudder that looked like more than a foot too long and guaranteed to hit bottom first in any grounding. Shame as the boat otherwise really impressed us, was immediately available and the price was good.
 
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