Wing keels and storms

kalanka

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I have a Sadler 34 fitted with the wing keel.

I am very happy with its general performance but have started to wonder how the keel design would cope with severe storm conditions. Seems to me that the keel shape would not be conducive to, say, side slipping down the face of waves but there may be some corresponding benefits.

I am not planning to head for the Southern Ocean but like to be aware of any potential limitations in the set up I have.

Does anyone have experience of wing keels in really heavy ocean weather? How did it go?

Thanks
 

Little Rascal

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No experience I'm afraid, but just from the theoretical point of view:

I would think the lateral resistance would be little different to the standard keel - otherwise you'd have more leeway also.

Although if you are talking about pure sideways motion, ie completely stalled, this might be different - possibly less tripping effect if there's less area. The wing is designed to increase efficiency by reducing tip losses so it's probably smaller than the standard keel?

What about ballast distribution and ratio? If you have less ballast or a shorter keel it's going to be more tender and have a worse AVS, but likely a less jerky motion.

There's also a school of thought that shallower boats have an easier time of it because they are less tripped up by the keel.

No idea how this would effect you in practice though! :eek:
 

NormanS

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Probably having the wing keel catching on fishing gear would stop you ever getting to the Southern Ocean.:D
 

Seajet

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Wing keels come about as a result of aircraft technology, particularly swept wing fighters, the design of which was first mastered by the Germans towards the end of WWII.

The idea of 'end plates', which is a large part of a wing keel's function, is to keep flow over the keel ( vertical aerofoil wing ) and prevent it flowing straight down off the end.

If you look at fighter aircraft wings, particularly Russian up to about 15 years ago, they were keen on ‘fences’ – vertical alloy plates on the wing to prevent this shedding airflow straight past rather than usefully over swept wings.

Please feel free to PM me for photo's, but I'm sure you get the idea.

A wing keel gives this benefit to a boat, retaining ‘lift’ to windward.

I’ve always wondered if the Anderson 22 keel, with a veed ballast bulb, has a slight ‘end plate’ effect, which would explain how she beats larger, on paper faster, boats.

There are snags with true wing keels though;

As they have been treated as a short cut to shallow draft by some designers, they don’t really get a chance, anything around 3’ or less is reckoned to be in the surface drift layer of a sea if in ( or just after ) a strong wind.

Also I for one really don’t fancy the idea of drying out on a wing keel & twin rudders, which the odd 1980’s boat proposed ( spiffing if one’s aground on a snooker table in a flat calm ! ).

They also tend to pick up flotsam.

Going aground, let alone drying out, in soft mud is a bit hairy – I’ve seen this tried – the wings tend to tip the boat over alarmingly far, then dig into the mud when she’s trying to rise on the unhappily appropriately named flood tide !

I haven’t seen many Open 60’s or similar performance boats with wing keels lately, seems they were a bit of a fad.

As for side slipping in gales, as the boat will be heeling and in the surface drift layer anyway, I can't see it making much difference, but I'll pass on experimenting; let us know how you get on !
 
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dt4134

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There's also a theory that the wings provide a more comfortable ride as they resist the boat being thrown around in heavy weather.

Certainly the winglets on the keel of my boat do seem to have this effect, but on the other hand they're lead and 2 metres down so that probably helps too.
 

Little Rascal

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Wing keels come about as a result of aircraft technology, particularly swept wing fighters, the design of which was first mastered by the Germans towards the end of WWII.

The idea of 'end plates', which is a large part of a wing keel's function, is to keep flow over the keel ( vertical aerofoil wing ) and prevent it flowing straight down off the end.

If you look at fighter aircraft wings, particularly Russian up to about 15 years ago, they were keen on ‘fences’ – vertical alloy plates on the wing to prevent this shedding airflow straight past rather than usefully over swept wings....

...I haven’t seen many Open 60’s or similar performance boats with wing keels lately, seems they were a bit of a fad...


I'm being picky here Andy :D, but leading edge wing fences are primarily designed to restrict transverse (spanwise) airflow on a swept wing and also reduce the stall propogation that results from it. They are also known as stall fences.

Wing tip bodies/winglets etc are an attempt to reduce vortex drag associated with the production of lift. Like you say this drag occurs because of the flow from one side to the other at the wing/keel tip.

The other method of coping with this inevitable drag is to go for high aspect ratio. Vortex drag (aka induced drag) is most significant at low aspect ratios and at low speed/high angles of attack. I guess thats why Open 60s etc don't bother as they have the benefit of high aspect ratio foils and overall higher speeds.

In a shallow draught boat the endplate or wing on the keel increases the efficiency (lift/drag ratio) to try to reduce the adverse effect of low aspect ratio ie stubby shoal draught keels.

Anyway sorry to go off topic!

I think ballast ratio and moment arm of a shorter keel will have more effect on you than any hydrodynamic effects in heavy weather. If these (and the stability curve) are the same as the standard design, then you might even be better off!

But as I said that's just an ill-informed opinion from a nice dry office! ;)
 
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Old Troll

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Old Troll

I find your wing keel discussion interesting. I have sailed a wing keeled yacht for many years often West of the Hebride in poor weather without as so much as giving the wing keel a thought. Certainly nothing detrimental about it. Never ever have picked up fishing gear or anything else on the wing keel. The yacht also sat quite nicely on the wing keel without falling after grounding on one occassion. I think perhaps there will be other priorities on an Ocean passage other than the wing keel. If anyone out there has other opinions on Wing Keels in heavy seas it will be interesting to hear about it.
 

savageseadog

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I have a shallow draft wing keel, I've not been in anything really big, perhaps 20ft max, never had a problem. There's never been a hint of instablity.
 

Seajet

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I don't think anyone was saying wing keels lead to instability, just that they have certain snags, particularly if tried to use by designers for shallow draft because of their 'low C of G'.

Little Rascal, wing fences on aircraft are part of a rather complex thing, including 'washout' to avoid tip stalling, and root sections to prevent a few other snags in the stall, be it high or low speed.
 

charles_reed

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Wing keels come about as a result of aircraft technology, particularly swept wing fighters, the design of which was first mastered by the Germans towards the end of WWII.

The idea of 'end plates', which is a large part of a wing keel's function, is to keep flow over the keel ( vertical aerofoil wing ) and prevent it flowing straight down off the end.

If you look at fighter aircraft wings, particularly Russian up to about 15 years ago, they were keen on ‘fences’ – vertical alloy plates on the wing to prevent this shedding airflow straight past rather than usefully over swept wings.

PS Suggest you look at Open 60s underwater configuration - they rely on daggerboards (up or down for directional stability) and a canting counterweight for righting. Think your comment has no basis in fact!

Please feel free to PM me for photo's, but I'm sure you get the idea.

A wing keel gives this benefit to a boat, retaining ‘lift’ to windward.

I’ve always wondered if the Anderson 22 keel, with a veed ballast bulb, has a slight ‘end plate’ effect, which would explain how she beats larger, on paper faster, boats.

There are snags with true wing keels though;

As they have been treated as a short cut to shallow draft by some designers, they don’t really get a chance, anything around 3’ or less is reckoned to be in the surface drift layer of a sea if in ( or just after ) a strong wind.

Also I for one really don’t fancy the idea of drying out on a wing keel & twin rudders, which the odd 1980’s boat proposed ( spiffing if one’s aground on a snooker table in a flat calm ! ).

They also tend to pick up flotsam.

Going aground, let alone drying out, in soft mud is a bit hairy – I’ve seen this tried – the wings tend to tip the boat over alarmingly far, then dig into the mud when she’s trying to rise on the unhappily appropriately named flood tide !

I haven’t seen many Open 60’s or similar performance boats with wing keels lately, seems they were a bit of a fad.

As for side slipping in gales, as the boat will be heeling and in the surface drift layer anyway, I can't see it making much difference, but I'll pass on experimenting; let us know how you get on !
Perhaps you're right in your conclusions - perhaps you're wrong. But it's easy to pontificate in blissful ignorance.

Having owned a wing-keel boat for 20 years, I can corroborate some of your opinions and offer refuting evidence to others.

First my wing-keel is not one of those little things that stops tip-turbulence. The wing is 1480mm wide on a 3m beam, is all lead and retracts completely, so that the boat sits on the wing, when dried out. The ballast-ratio is 40%.

The considerable wetted area of this wing definitely slows the boat in light winds and, my experience is that it has a magnetic attraction for any lines in the water.

Conversely, in any breeze it is a considerable aid to stability. Above 6 knots through the water, the 6 degree dihedral increases stability and makes the boat behave like a longer, heavier boat. in still water, on main alone you can tack through 35 degrees and get drive under main alone. Leeway is non existent, until wave-action (I've been out in 54 knots) drives the boat sideways (with no tripping).
When sailing fast, in quartering seas, the stability of the keel versus the action of the quartering seas means that the boat is driven off course by the wave, but soon recovers from the broach.

As to drying out - you have to choose a relatively flat area - it is, surely, illogical to expect a boat to remain level on a sloping surface?

One last point; lifting off mud or soft sand produces the greatest "sticktion" effect, which can be quite worrying as the waters rise above the boot-top for a few minutes.

What the wind keel does is to dramatically increase windward ability (not that anyone in their right mind wants to always go to windward), dramatically decrease pitching at higher hull-speeds at the expense of light-wind performance.
Best of all one doesn't have to suffer the consequences of improbably designed cradles (having watched 3 boats tumble over in the last 4 weeks it matters) when on the hard.

PS I suggest you look at Open 60s undewater profile again - reliance on daggerboards for directional stability and a canting counterweight for heeling resistance, leaves little option for a fixed wing keel - a spurious argument?

PSS What about all the later model 747, 737 319, 320 etc which have all fitted winglets - enough about interceptors, which we all know are designed to be inherently unstable unlike a civil aircraft.
 
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Seajet

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Charles,

Maybe I phased it badly, but you seem to be agreeing with my thoughts !

Possibly one of the best features of wing keels is the 'damping effect' on otherwise lumpy conditions; not too convinced about drying out though, a chap at my club was talked into a wing keeler by what sounds like a brilliant salesman, tried one tide on our drying moorings then as he'd just inherited some money high-tailed it to a cheap mooring in France !

I saw the boat dried out on her ear ( and it's very soft mud there ) which didn't look too hopeful, but I must admit the guy's an idiot at the best of times.
 

Little Rascal

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Andy, I wasn’t disagreeing with you - ideas like stall fences, washout, etc all just ways of manipulating stall behaviour, which is a particular problem because of the tip stalling tendencies that come with a swept planform as well as the span-wise stall propagation I mentioned.

Charles, good to hear your empirical experiences - as I said I'm certainly ignorant - but not feeling too blissful about it though!:D

From what you say about leeway, it seems that the wing keel is very efficient above a certain speed.

Open 60s: Are the dagger boards asymmetric? Either in the camber of the foil itself or in the angle of attack relative to the boat?

747s: The majority of new commercial aircraft will have wingtips (Whitcomb type etc) They are designed to actually increase lift at cruise speeds, resulting in quite a significant gain in efficiency and fuel reduction.
 

DownWest

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Interesting that Charles' wing has 6 deg dihedral. The odd one I have seen and the pics of the Australian 12m keels show anhedral. IIRR Warwick's(sp) 'twin' keel was flat bottomed and sloped down beam wise, so also anhedral.
A
 

rudolph_hart

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I have a wing keel, and here's my 2 pen'orth:

I agree with Seajet's comment about laying over further when drying out. It's very scary - I've done it :eek: Think of 2 red wine glasses lying sideways on a tabletop, and one of them has the base snapped off (i.e. no wing).

I concur with Charles Reed's comments about windward performance and dampening of pitching (which gives her a motion of somewhat bigger than a 35 footer.

I don't know Anne Headrell or her sister Di, but the keel shape is not that simple. I have a picture of her in the yard, but I can't master the posting of 'em on here, so here's a description:

From the side: Leading edge is almost plumb, aft edge raked about 45%. Wing attached from halfway along foot to level with aft edge of the keel. Wing bottom surface is flat. Top surface is aerofoil shaped & gently curved down towards the forward edge (to pull the boat to windward when heeled?)

From forward: Top of keel is about 6" thick and 14" or so at the foot (shaped rather like a spring onion). Wings are about 4" thick at root and 3" at tip. Top and bottom edges of wings slope downward. The entire keel is a single iron casting.

I bought the wing version because of her draught of 1.5m (standard is 2.0m ) - useful on the E. coast. My worry that the reduction in draft would make her tender (30+ sq m mainsail) was unfounded.
 

Beadle

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I think you misread Charles' post.

He sails a Parker 31 who's wing keel retracts so that when she takes the ground the hull restc on the wing making a very stable platform.

I will second his other comments re the Parker 31. _ sailed one for 7 years and sold it 3 years ago. And still wish I hadn't they really are superb boats, its a tragedy that Parkers have folded.
 

rudolph_hart

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I think you misread Charles' post.

He sails a Parker 31 who's wing keel retracts so that when she takes the ground the hull restc on the wing making a very stable platform.

I will second his other comments re the Parker 31. _ sailed one for 7 years and sold it 3 years ago. And still wish I hadn't they really are superb boats, its a tragedy that Parkers have folded.

Just wasted 1/2 hr composing a helpful reply, and attaching a wing keel photo, only for the F'in thing to crash out with Server Unavailable message, so I give up:mad:
 

BlueSkyNick

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Just wasted 1/2 hr composing a helpful reply, and attaching a wing keel photo, only for the F'in thing to crash out with Server Unavailable message, so I give up:mad:

Is that F'in as in Fin keel?! sorry can't help it sometimes :eek:

I am guessing you are sailing a Starlight35 Rudolph. Searching for a 39, I am very interested in this thread.
 

rudolph_hart

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Is that F'in as in Fin keel?! sorry can't help it sometimes :eek:

I am guessing you are sailing a Starlight35 Rudolph. Searching for a 39, I am very interested in this thread.

No, she's a Dehler 35 CWS. The Starlight's are well sought after, and I get the impression that 39's for sale are as rare as rocking horse s**t.

Keel photo:
 

kalanka

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Wing keels

I appreciate the thoughtful (and technical) responses. Thanks!

My experience is that the wing keel is an excellent all round performer. One loses some windward performance but there is a significant saving in draft and very nice damping of the boat's motion in lumpy water.

Some time ago, I embarrassingly ran aground on hard sand and had to wait a tide to refloat. I have some heavy duty yacht legs which were deployed with some haste but the boat dried out completely, heeled at about 15 degrees on the inclined edge of the narrow channel I was trying to follow. I felt strongly that she would have been pretty stable without the legs but was very glad not to have to test this for real.

I think that once the boat touches with any force the wing keel tends to be stuck - the classic response of heeling the boat doesn't seem to achieve much.
 

William_H

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Wing Keel

As I understand in really big seas when beam on to the waves the real danger is that thee wave in breaking accelerates the water near the surface while the deeper water remains stationary. Thus a deeper keel is stuck in stationary water while the surface water supporting the hull accelerates to lee ward thus tripping the boat over in some cases right over. So in this theory with a shallower keel you may be much safer in breaking waves than with a deep keel. Retracted keel even better provided you have ballast low enough.

Back years ago when Americas cup boats were practicing for the defense of the cup in Fremantle the story goes that some guys were fishing in deep water while anchored. Suddenly they found themselves doing 12knots towed by a 12metre yacht the winged keel of which found their anchor line.
The wing on the 12metre yachts was as much to beat the measurement rule as anything else. Deeper draft having a penalty on measurement. A winged keel did not. It was also thought that the leeward wing would when heeled act like a deeper keel. This wing could also perhaps be given some angle of attack to give lift against leeway. Plus of course as mentioned the restriction of vortices with water flowing off the end of the keel.
Regarding aircraft wings it is interesting to note that the theory has been around for a long time. Yet not all aircraft fit winglets on the ends. So the advantage is not always clear given the drag involved.
I think in most cases a good high aspect ration foil is best on aircraft or boat.
However if shallow draft is a priority then a wing works better than a low aspect ratio keel.
 
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