Size of Daggerboards

Hello out there,

I'm new (to this forum and cat sailing) and got a Sol Cat 18
10 days days ago, that is now nearly ready to run again.
I'm missing the daggerboards.
I spent some hours reading thru this forum. Looks as if I can go without those. I also found hints/links to websites who from time to time have them. I got another tip from a nice guy here that I could use the Nacra 5.2 boards. (very expensive though )

What I would like to do is to recreate the original ones, but although I found some pictures here on some of your links to the Sol Cat (thanks CaptainScurvey !!!!!),
I don't see fit to build them from those.

So I would really appreciate if someone out there has a better picture, catalog page or even some measurements for those boards that could help me ?

Thanks for any help and you all have a windy 2005
(no hurricanes of course

you should make them with the same area of a nacra 5.2 or alittle larger. you can always cut them down later.
type daggerboard or something like naca foil in a search engine to get ideas for construction. it can be as easy as cuting them out of a sheet of aluminum and rounding down the corners.
a perfect fit in the trunk will minimze water shooting up the trunk which is drag. on the other hand, if sand gets in a trunk with a perfect fit, the board can get jammed.

Thanks Dave,

I spent quite some time looking thru the net and this board the last days, but couldn't find any measurements for daggers, except some quite crude square one. Googleing the NACA key words was much fun. In case I find my old math books, I might understand parts of what I found there

What I'm looking for is just an idea about the shape. On one of the pictures I found the SOL CAT daggers looked quite amazingly formed with several curves ????

Thanks again

The number you are looking for is 2% of the sail area right out of a text book on sailboat design.

Thank you BillRoberts,

thats a start and I can think I can handle 2%.
Is this for one dagger or both ? and I assume its only the
part poking out under the pontoon ?

I had a Sol Cat 18 and a Nacra 5.2.
The daggers were very similar in size, but I never laid one on top of the other.
The Sol daggers weighed twice as much as the Nacras.

The 2% number is total daggerboard area, both daggerboards, based on total working sail area.
As I remember sol cat daggerboards, they are very thin. That is why they break so often. I doubt that you will be able to find any from another boat that will fit the sol cat daggerboard trunks.
The least expensive way to get sailing is to make some boards yourself out of vertical grain douglas fir, strong wood, and paint them.
Bill

Thank you guys,

thats a good start. As I'm a newbie on cats, I think
its not so important that they are exactly like the original ones. I think it's smart to follow your advice with the 2 %
area and make them thin enough to pass thru the trunks.

I had the impression I had to build something sophisticated,
with curves and such so they would move backwards in the trunk if I hit something underwater.

Thanks again for your time and knowlegde

I doubt that there are any daggerboards that move aft when you hit something. centerboards do that, and that is the main reason that the Tornado has centerboards instead of daggerboards.
the top of a daggerboard is cut back so that when they are up, there won't be a sharp trailing edge staring you in the face. should you hit that trailing edge with some part of your body injury is likely. the hobie 18 daggerboards have lovely curves. The curve on top, on the aft edge is for this safety factor. The curve of the leading edge under water does allow the boat to ride up on them (somewhat) should you beach with them down. This means the boards must be somewhat wider to get the needed area which inturn gives them a lower aspect ratio and less effcient lift. It was a compromise for safety and usability for surf sailors.
hope this helps

Some windsurfers use a pivoting daggerboard and it works very well. A schematic picture is attached.

Cheers,
Luiz

most current F18 designs have a rounded leading edge, not for occasional bumping the ground but for better flow with reduced tip vortex. Seen here is a Nacra F18. The Hobie Tiger has a very similar shape (or rather - the other way around!) with even more curvature on the leading edge tip.

They are called centreboards.

They would in case they had freedom to rotate only, but unlike a centreboard, a pivoting daggerboard has freedom to rotate AND to move up and down like a daggerboard.

Summary:

Daggerboard - one freedom of movement - up/down
Centreboard - one freedom of movement - rotation on axis
Pivoting daggerboard - two freedoms of movement - both of the above.

Another drawing attached.

Cheers,
Luiz

Woops, thank you all for the attention and time.

If this goes on, I'm becoming a specialist on center/daggerboards

Your posts explains the pictures I saw in a catalog with daggerboards with curves on the upper side.
And I had this "hitting and moving" thing in mind from old experiences with windsurfboards and the diagrams are explaining that quite well.

Thanks you again