I was talking to some folks about building rudders and daggerboards and the question came up how many layers of graphite fabric would be right and the ounce rating. I have seen ounce ratings from 5.7 to 10. It appears your first layer would be fiberglass cloth then with 1 or 2 layers of carbon fabric. Join the 2 halfs and fill with expanding high density foam. I am planning on building a rudder for a F28.



What kind of techniques are used to join the halfs?

I used a slightly different method to build a rudder. I purchased a sheet of rigid crosslinked pvc foam, cut and sanded it into a core then covered if by wraping the glass so that the ends of the cloth came off of the trailing edge, then trimmed off the excess after the epoxy set. This saves you from building molds and is much more resistant to splitting. If you use unidirectional carbon cloth lengthwise down the rudder it will be able to use fewer layers since it will be oriented to the direction of the largest forces. My rudder was just for an old catalina 25 and it was severely over built with 3 layers of 10oz unidirectional e glass and 2 layers of 10oz biaxial stitched material. I would think that 2 layers of each would be adequit even for your application. If you do use a biaxial stitched material, get the +45 -45 oriented rather than the 0 90. I found it much easier to work with.

Good luck, keep the epoxy out of your hair.

Mark,

I have photos of the process described in the last post on my web site.n (I think under carbon components or similar)

I used 4 layers of 200gm (approx 6 ounce) Uni carbon ,

2 at 0 deg and 2 at 35deg covered by a layer of 6 oz plain weave glass.

A layer of glass on each half before I sanded the shape with sand paper glued to cedar cut to profile. This layer of glass gave an absolutely briliant trailing edge.

I have posted a detailed description on the old forum a long time back.



Hope this helps.

Phill

Phill,

Here is a copy of the rudder and board message you posted to the old forum. You humbley labeled it "Low Tech Carbon Foils" It will probably help Mark.

We all thank you.



------------------------------------------------------------

Low Tech Carbon Foils



Posted by Phill Brander on December 29, 19100 at 05:28:04:



Just in case there are any peple out there wanting to have a go at making some light weight foils.



I've posted some pics on my web page (under "Chined Construction") of the boards I'm building. They really quite light and incredibley stiff.



The way I went about it is as follows:-

The rudders and centreboards I made by plotting a NACA 63009 section onto a section of aluminium for each. Then I filed it to that profile.



I screwed this to a peice of cedar and used a router with a ball bearing bit to cut the cedar to the shape. Then glued some 100grit sandpaper to the cedar. This is to shape the foam.



I used styrofoam rated at 300kpa. Ordered a 50mm sheet cut into 3 8mm sheets and 2 10mm sheets. Used the 8mm for the rudders and 10mm for the centreboards.



So I obtained a sheet of plate glass. Applied some PVA as a release agent.

Wet out some 6oz glass and vacuum bagged the foam to the glass. Then I set up a jig and used my cedar block with sandpaper to shape the foam. The glass backing stabilised the foam and allowed me to get really good trailing edges.



Once this was done I routed out the foam of each rudder half where the rudder passes below the rudder stock and replaced it with cedar as a core that tapers away several inches below the rudder stock and goes up to the top of the rudder.





The rudder layup was one layer at +36deg and one at -36deg, top to bottom.

One layer straingth down the foil top to bottom and one layer straight but only

half way down. Then one layer of 6oz plain weave glass over the carbon.(just something to sand when finishing them instead of weakening the carbon)



Anyhow I vacuum bagged the layup and then cut away the 6oz glass and 20mm of foam from the leading edge of the rudder and bottom and filled this with glue before vacuuming the halves together.



The sectional shape is exactly the same as my aluminium profile over the length of the blade.



Both rudders and centreboards seem really true.

They should be as true as the plate glass I used to vacuum them against. At least that was my theory.



The layup of the centre boards was similar but I used end grain balsa where they pass through the bottom of the hull. Also the top of the board has only two layers of carbon as does the bottom while there is 4 layers where the board goes through the hull.



I used 8 metres of 300gm uni for two rudders and another 8 metres for the two centreboards. (They weigh about the same.)



The centreboards are 960mm long 210mm wide and weigh 1250 grams but they still need the top coat of polyurethane. But that won't add much weight. I doubt it will add much more than 50 grams.



Regards,

Phill

NaCl H20,



Thankyou very much.



Phill