The lift/ballast Configurations
 Fixed ? Waterballast ? Swing ? Articulating & Swing ?
 
Swinging 3D ? Slide longitudinal ? Slide side to side ?Slide & Swing ? Trimtabs ? Daggerboards ? Free moving daggerboards ?
EVOLUTION !!! INVENTIONS !!! WHACKY IDEAS !!!

In the Mini Class there seems to be two popular keel choices.
The fixed keel or the swing keel version.
And then there are the more experimental ways to go.
A sliding keel (Rolland, 97), a sliding/swing keel (Rogers design 99) or a 2d keel swinging rotating keelfoil (Raison), a 3d moveable keel (Lucas, 99).And more...

Function of a keel;
Basically the effect is that the boat will not slide sideways but forward (lift).
And for stability you give it weight. A normal keel is symmetric so it works efficient on both tacks.
A trim tab makes it asymmetric and makes it possible to sail more to the wind, or the same course with less drag, or install a thinner foil which give less drag..
To change the keel foil angle of attack can reduce the drag, or improve streamlines.

A bit of history:
The first minis in '77 had the fixed keel, how normal.
Then in 79 we already had a revolution, there was a waterballasted entry, the American Express. This boat won and prove the usability of waterballast in long-distance racing.

The first swing keel was first used on an open 6m50 in 1991 by Michel Desjoyeaux.
According to his website "I had trouble with my rudders, so in the first leg I came a week later then the first boat on the finish. But I proved the value of the swinging keel in the second leg. I won this leg."
Michel mentioned that there were other boats earlier fitted out with this concept, but he did the first serious offshore long distances with it. Seems that Michel is a honest guy, credit to creditor. (have to say that the rest of this article is maybe a quarter of my own thoughts and a compilation of discussions on the Open Class Sailing Forum, articles in Seahorse, websites, and some articles people mailed me, thank you all.)

Since then the debate of which type is faster is going on, as the both types are still being build and sailed and designed by topteams and designers.
In the years later there are tried a lot of different approaches, like the 3d keel.
But first I will give a comparison between the fixed and the swingkeel.

The fixed keel;

Yes that can be the normal keel you find under most modern boats, a fin strut with a bulb. That is what the one design Pogo is using.
Already in '79 Norbert Smith decided to go for
waterballast so he could make the bulb lighter. The reasoning is as follows;
You design a boat so that it can sail upwind, that means that you have to counteract the heeling forces that the wind gives in your sails. So you invent the keel. Then you notice that if you move your body around that you can counteract the heeling forces too !!! (that is the way unballasted dinghy's sail ) So you decide to make the keel a bit lighter and you have to move your body around to sail optimum. The boat is a bit lighter and thus faster. Now it would be handy to have more bodies on the rail, like the fully crewed races have ! You can chip away more lead from the keel. But hey, this is single-handed racing. So you figure out that water could be a handy replacement of that meat. The fixed keel with waterballast is born.

So the difference between a fixed keel and a fixed keel with waterballast is;

 Fixed

Ficed with waterballast

Always the same weight.

In heavy wind the same weight and stability, in light wind you dump the waterballast.

Nothing to trim.

You can be caught with the ballast on the wrong side, by an involuntary gibe etc.


So in light weather a waterballasted boat is lighter and faster. It can be from 70 to 100 kg lighter. It comes more out of the water, less drag, the keel bulb is slightly smaller and so a bit less drag. And a little lighter construction.
The system to get water in and out is extra weight. That counteract the weight difference a little bit. But overall a faster boat. Upwind and downwind. Except in the upper limit of windspeed. But it is more work and tacking is slower. And it takes space in the boat. Another advantage is that you can overload the ballast to gain some momentum in heavy wind. Take another 100 to 130 kg water in and you have a better upwind ride. You can fit off course this to a normal fixed keel boat too with out the weight reduce in the keel, but that is a halfway approach.
Another point is that the water ballasted boat has the pumping etc. already in place. But it makes a difference later when we compare waterballasted with swingkeelers.

So the boats became mostly waterballasted, the Class Mini organization put a limit on the maximum volume of the waterballast. That to enhance safety.
Note; we are talking about waterballast stored high up in the sides of the boat, not the waterballast some trailorsailors use to make the boat heavier, this is stored in a double hull or tanks on the bottom of the hull !!!! That is another story...

Then came Michel Desjoyeaux along with his swingkeel.

PicturePicturePicturePictureHow does a swingkeel looks and how does it work ?
See the picture and follow this theory.

PictureTo have weight up on the high side (like the waterballast or people) works, it effect is more righting moment. Shifting water from one side to another can be a hassle. It takes time, and if you are broached and want to tack quickly (or are being tacked, grin) you have the ballast on the wrong side. So there must be another option. If you make your fin keel with bulb movable from side to side it would work nice, again you have the weight where it is most needed. The high side.

Now is moving your keel from one side to the other a structural nightmare and the  solution is to make a hinge in the bottom of the hull where the keel is normally positioned. But how can you change the angle of the keel ? Normally a keel strut ends at the bottom. Now you let it stick through the hull, place the hinge at the hull-bottom and there is a stick in the cabin what you can pull/push to both sides. On a mini you use a block and rope solution to adjust the angle.
There is however a problem to get this through hull keel watertight, so in those boats you see a box in which the stick can move. It will take up a lot of room, will never be totally watertight and the ropes and blocks are always in the way. But you can wash your dishes there.

Another aspect is that if you swing your keel the keelfoil (the strut between bulb and hull-bottom) is to at an angle. This strut is normally designed so it produces the best lift and less drag as possible. But what happens if you protect this foilshape at an angle ? Look at your sail, if the boat heels you will see that the wind will spill and will not be 100 % effective in pushing the boat forward. To clearly see this exaggerate this, your boat is is heeling 80 degrees. The wind is just flowing over your sail without creating a driving force. The same applies to a foil. It becomes less efficient. It even became so inefficient that it has to be solved. The solution was to make the keelfoil as draggles as possible and let daggerboards take over the lifting force. (It goes to far to describe why you need lift, if you have problems with this, there are a lot of good information's to find on the Internet.)

Now you have a swingkeel with daggerboards to handle, in name of less friction and more trim the daggerboards are made lifting up and down. On the Minis we see that some boats have the daggerboard midship, before the swinging keel. Or the solution with two daggerboards on the sides of the boat. The two daggerboard solution has upwind only one board down. A daggerboard improvement was to make it self tacking, just a daggerboard case with the trialing edge to wide. This will angle the daggerboard so it creates more lift. Only if the boat has one daggerboard off course.

Other points;

The weight of a swingkeel is theoretically a bit lighter then a fixed keel. But you need daggerboards and casing, so you loose weight advantage there.
The strut can be designed very efficiently in low drag, no compromise have to be made for creating lift. But it can result in humming and vibration. The daggerboard can be designed more efficiently in lift. So the extra weight of swingkeel and daggerboard has as return a better lift. Or is the drag of the strut still to much, specially when the strut is canted it is "draggy". That is upwind, downwind the daggerboard will be more up. I have never seen tanktest results of this, anyone has seen them ???
For momentum upwind the swingkeelers use a water ballast tank, but not for a better righting moment but for gaining momentum. So there is a plumbing system needed too. I will linger on about the momentum that is required. Open 6m50 are so light that they need more weight upwind to sail over the waves. Otherwise they will be stopped by every wave. Not only 6m50 uses it, too for open 60's and Volvo 60's. But on a Mini it is more influencing the comparison. A hundred kg more is a lot on a mini of 800 kg. it has a big impact. It turns out that the Mini with swingkeel and momentum water ballast is slower upwind in medium to heavy weather. It is heavier then the waterballasted fixed keeler.

Getting overwhelmed ??? You are not the only one...
One simple rule I have read;

If you use the swingkeel use at maximum angle you will be lighter then the fully loaded waterballasted boat (and your ballast is in a slightly better position). In this situation you will be faster. That will be reaching and running in moderate and heavier wind. In light wind the waterballasted boat can dump the weight on those courses and be faster. For upwind in heavier conditions I wrote about the momentum ballast and that the swingkeeler is slower.
I heard that in very light wind the swingkeeler is faster due to the ability to let the boat heel, thus creating less wetted area.

Waterballast & Fixed

Swingkeel

Tacks slowly

Tacks faster

Is lighter without water.

Is heavier. Until WBted is fully loaded

Does not require daggerboard

Needs daggerboard

Faster upwind heavier wind and in light winds

Is faster at the rest of courses.

Has pumping equipment

Has the tackle and ropes and clutches.

Has tanks inside *

Has a hinge and waterbasket inside, and a central waterballast tank. *

* both options leaks and can fail, it is a personally choice witch you preferPicture

An other aspect is that waterballast is high up in the boat, and the bulb of the swingkeel down below. This as an influence on the VCG of the weight.
Creating more moment for the swingkeeler then for the waterbalasted boat.

In the '99 edition there was a variety of all types racing.
On the finish it was a win overall for a swingkeeler, Sebastian Magnen with his Karin Liquid. Did he had a significant lead ? No it was a fight against fixed keelers with waterballast and other swingkeelers. The first finishers were quit close. Second (Peter Heppel) on the second leg was a fixed keel with waterballast. However this was a special one with a trimtab, see later. Third was normal fixed keel with waterballast (Taberly). And to show that the old fashioned fixed keel without waterballast can be quick, the first Pogo was 8th.

In 2001 the whole podium was filled with swingers, but the slide swing of Rogers did lead the 2 leg for long and did finish 2d that leg. The fixed keeler did perform again quit well, and the Pogo did finish again in the top ten. It is not that swingkeelers are beating the fixed keelers in a big way. More a subtle way, but specially in the second leg the swingers seems to be favourite

So it shows that you can discuss this choice, but still you have first to learn to sail fast.

And what about the other keel types ?Oh yeah there is more.

A promising one is the use of trimtabs with a fixed keel.
In short a trimtab is the last piece of the keelfoil made so that it can rotate. It looks like a rudder mounted behind the keel. If you deflect this there can be a win in lift.
Or have the same lift with less drag. Promising stuff, Peter Heppel used it in the '99 MT. He used it together with waterballast. And to be clear, it was a fixed keel.
In Seahorse he writes "Downwind, keel area is only drag. Upwind, even with other appendages to help, the keel has to produce a lot of lift. Maybe it is a habit from my IACC work, but I decided on a trimtab. This gives a minimum-sized keel, with the chance to increase its lifting capacity when needed. "

If you have followed the IACC you will have seen that al but one team went for one rudder with a fixed keel wit trimtab. And we know how much money those guys spend on research...
But does it work on a mini ? Apparently. Some figures I have from the IACC world (source to be unnamed ;*) ) is that the trimtab keel with the tab deflected 8 degrees generates the same amount of lift as a keel twice the size !!! The tacking angels are a demonstration how efficient they are. But an IACC boat is something different then a Mini Transat. It surely seems to improve the waterballasted fixed keel design.

Then the sliding keel.

I first saw it on Chris Pontets Rolland designed Speedy Pym in '98.
It looked quite simple, it is a keelfoil that sticks trough the hull, on top of it is a carbon pole mounted (in the for and aft direction). This is hanged in two brackets. One behind and one before the keel and space designed to slide. All this in a housing  because it was not watertight. On the brackets were locking cams to stop the keel from involuntary sliding.  And there was a glassfiber thin plate before and after the keelfoil. This was at the bottom of the hull, to keep water from sloshing in. They were moving with the keel.
On my question how it functioned in practice he remarked; " it seems that the keel always performed best when it was slide the whole way back. Anyway to keep it adjusting is a lot of work." In 2001 I did see the same hulltype with the keel fixed and placed way back.

A keel that can slide from side to side:
This is to create an extra bit of momentum, harder to build, the track inside is curved so in the mid the keel is centered, but on the side it changes the Angle Of Attack to 5 degrees. More lift. You do not need a daggerboard, but more keelfoil out of the water... www.elie-canivenc.com


A 2d keel ?

This is a swingkeel with an added feature, it can change the angle of attack.
I will copy the remark of the designer/engineer here. Raison of Lucas/Raison:

"Hi Leo, I read with interest your page about keel systems and I'd like to give you more detailed information about the keel systems we designed with François LUCAS . The first system was a 2D keel which can be canted and trimmed (x and z axis)Picture. It was designed for my Mini n° 232 (Savoy Truffle). It works with a High strength stainless steel 2 axis device trough which the keel is fitted to the hull bottom. Longitudinal stresses are

Photo´s Raison. to lazy to rotate the 2 photo, 3 is the damaged bulb.

compensated by the keel basket top and the keel is easily canted and trimmed trough a block system. It appeared that this system was amazingly strong because it suffered no damage when I went ashore during the second leg of Mini-Pavois on the 26th of may although the keel bulb was really damaged." "The trimming is very efficient in upwind and reaching conditions as soon as our wide wide boats are heeled because it reduces the hull and keel induced drag."

And then the 3d keel ?
Picture
That is developed by Lucas. It is a keel with a ball joint instead of a normal "doorhinge" used by swingkeels. This ball can be adjusted for and aft and sideways. this all simultanisly.
So you can move the bulb in any position, a inch forward and to the right ? You ask (or pull the ropes) and it can be done. See rough and over exaggerated animation I have made. An effect is that the projected area of the bulb changes as you cant forward/afterwards. That is the gray area that appears on the rearview. The design of Lucas has that fixed by a moveable bulb that automatic keeps the bulb straight.. As Lucas was very helpful with information I created a special page for this concept.  Click here......

And what is there more floating around ?
The sliding swingkeeler !!!
The innovation of 2001 !!!


PictureThe swingkeel that you can slide forward and back. This is a combination that asks a lot of practice to, but can be the next step up. The Rogers design had that in 1999, I thought that there were more tries in that direction by multiple designers. Photo;Thompson

In 2001 Brian Thompson sailed this design, in the first leg he had a leak in the waterbox, meant 300 kg extra ballast and he was slowed down. In the second leg he was leading a long part of the race, only being overtaken in the last day. So it proved fast. And I think this will be followed. It is the equal of having a guy walking to the back, that helps for surfing and anti nosediving. And in lightwinds you slide the keel forwards so you get less wetted surface. the designer is keen to design such a keel for a larger yacht ;*) He just looked good how a fully crewed yacht places the crew in different situations and try to copy that with the keel.  (update 2003, Rolland has designed at least one swing/slide,codeM)

Or is the future a fixed trimtab keel with a trimtab daggerboard ? Or are hydrofoils coming ? Or will some one try the CBTF technic on a Mini (edit, already done in the 80's, did not work then)? Even if that seems to favour skinny slender boats.

Transportation and the keel:

For transportation you have to remove the keel from the boat, for shipping it back to Europe after the Transat650 for instance.
The solution is by making it able to loosen the hinge of the swingkeel, remove of a piece of the deck (right above keel) and let the boat slide over the keelstrut/body. This makes for a nice compact delivery ;), OwenClarke has it, more designers must have designed it too...