Infusion - jybing dagger boards?

I believe gybing centreboards are popular in 505's.

Dave:

Your question can be taken a couple of ways. Are you asking the physical way they work or whether the catamaran performs better with them?

As to whether they work better. I am kind of surprised that they are on the Infusion. When Pete and I took the boat out with both set ups there was no real obvious performance difference. He was thinking of scrapping the idea. That was only tested one day though. He has since gone back to the drawing board and decided that on paper it will be worth it. The last time the boat was sailed, actually hull #1, everyone on the boat liked the way it sailed. They got the balance on the helm exactly right, it was agreed. The new standing rigging is really nice. The sail is going to get just one more iteration, making it a bit fuller.

If you are sailing the Gybing boards you will have to pull them up downwind. They apparently can get out of sync. I think that 1/2 way is fine.

As for physically ("how they work") in case that was your question. Imagine that the dagger well is bigger that the board. That makes a kind of a sloppy fit, so bind the back of the board to stay in place. That leaves the front to move back and forth. The pressure of the wind is pushing the boat against the water and turning the boards to lock the leading edge a bit into the direction of the wind. It is not very much. They are designed for better performance going to weather. Maybe they should be called tacking daggerboards? If you own the boat and do not like them Gybing it is just a matter of filling in the gap.

Later,
Dan

Hi Dan,
Yes that was what I thought..that the front of the dagger well was a bit big and let them move from side to side a bit..
Thanks,
Dave
PS, any new pictures or a video coming up?

I think a few F18's before the Infusion have tried the gybing boards already. Mystere Twister is one that comes to mind and Mattia F18 as well. Although I'm not too sure about the last. For some reason it has not gotten of the ground in the F18 class. Of course in the monohull world it is a relatively accepted feature, but then they have only one board !It will be interesting to see if this feature will remain part of the Infusion design or go to way of the earlier tries.

I put this post down as some background historical info.

Wouter

The following explanation and pictures were taken from here - scroll for "Gybing heads".

Gybing Heads

Some boats use what is known as a "gybing head" design. If you look at the following picture, you can see that the head is trapezoidal in cross section, rather than the more typical rectangular.

What this does is allow the centerboard to pivot inside the centerboard trunk (rotating about the point of maximum thickness of the head). The forces causing the board to pivot are (1) the lift being generated by the foil, and (2) the lateral resistance from the foil preventing the boat from slipping sideways through the water. Usually you can view the lift vector as being concentrated at the 25 % chord, while the lateral resistance is more or less evenly distributed across the foil. If the pivot point is greater than 50% back from the leading edge of the foil, then the forces will cause the centerboard to be pressed against the side of the trunk, and it is "gybed" into position. Typical centerboard gybing angles are about 3 degrees. The centerboard only gybes when it is all the way down - as soon as you start to rake it back in the trunk, the fat leading edge of the foil will jam enter the trunk and cause the centerboard to jam in a straight fore-aft position.

Why do you want a gybing centerboard? By the board rotating to windward, you increase the angle of attack of the centerboard with respect to the centerline of the hull, and therefore generate more lift, all else being equal. In practice this means you can steer the boat slightly lower and sail with a fuller jib for increased power while maintaining the same leeway angle as a similar boat with a non-gybing board. That's the theory - some fleets like them, some don't (and many one-design classes don't allow them). Frank Bethwaite in "High Performance Sailing" claims they are a bad idea as the rudder may end up directly in the disrupted flow from the centerboard.

Click here for a short overview of the fabrication process.

A single gybing daggerboard may make sense in a mono but why not just use asymmetric boards to generate more lift on a catamaran ala the big twin daggerboard monos/cats/tris? You could conceivably have the bottom half of the board symmetric so if you left it down while going downwind it wouldn't "hurt" you-

Kirt

I have a feeling our Capricorn may have gybing boards. We have quiet an unusual shape at the head of the CB and have been noticing movement it the board.

Will check it out further and try and get a pic.

These Gybing boards are completely foreign to me.

captain kirt:

Seems to me that making gybing symmetrical boards would be more cost effective in the long run than assymetrical boards.

Asym boards are not legal in the Formula 18 Class.