The lift/ballast Configurations
In the Mini Class there seems to be two popular keel choices.
Function of a keel; 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.
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.
To 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 thewrong 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 strutends 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.
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 bestlift 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. Thesolution 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 thedaggerboard so it creates more lift. Only if the boat has one daggerboard off course. 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. *
Waterballast & Fixed
Is lighter without water.
Is heavier. Until WBted is fully loaded
Does not require 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. *
In the '99 edition there was a variety of all types racing.
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 thetop 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
A keel that can slide from side to side:
This is a swingkeel with an added feature, it can change the angle of attack.
And then the 3d keel ?
And what is there more floating around ?
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 walkingto 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 hydrofoilscoming ? 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.