Rudder & Daggerboard Foils

Constructing A NACA 0012 Rudder and
NACA 0010 Daggerboard Foils

Part 1 - Cutout and Assembly
Part 2 - Fairing the Foils

A daggerboard or rudder can be made from designed stacks of 1/8" (3mm) plywood strips. This can be done without all the hand cutting, shaping and sanding from solid materials like plywood or dimensional lumber. Try to get marine grade if you can find it, but a good quality of 1/8" plywood can also be used. The non-marine grade plywood's, as well as the marine grades, will be covered in fillet material, epoxy, and a good coating of paint. So water penetration issues should not be a problem. The only place where marine grade plywood should be used; is in a daggerboard, centerboard or rudder that is attached to a hull kept in the water most or all of the time.

There will be 8 strips of various widths and lengths to make a daggerboard with a NACA 0010-10 cross section. The 0010-10 designation means that the formula works out to be a daggerboard that has a cross section of 1" @30% from the leading edge and a cord length of 10" and is a "lifting foil". The rudder is a NACA 0012-8. It will look a little thicker for it's 8” fore and aft length, even though it to has a 1” cross section thickness; and will also be made with 8 strips. This laminated style of foil section also makes it easy to hollow out a spot to place lead bars or shot to weight the lower end of a swinging centerboard and help it go down.

Start by studying the plans to determine the size of each of the matched pairs of strips. Note the arrows on each of the strips showing the direction of the top grain of the plywood sections. This will ensure that the finished daggerboard and rudder will have the greatest resistance to bending and twisting. Set the guide on the saw of your choice to the width of one of the panel strips. Do some pre-planning and layout of the strips to see which of the narrower ones can be cut from the wider strips so you don't waste wood. Remember that there are only "two" strips of each size for a total of four “matched pairs”. So you will have eight pieces for the daggerboard and eight pieces for the rudder. Stack them in mirror image sets.

Lets start construction of the daggerboard. Take the two biggest strips and match them up along their ends and sides and clamp together. On the upper strip of the pair, lay out the starting and ending points for the "arc of the tip". There is a measurement for the leading and trailing edges of the arc; and one about halfway up the trailing edge. Mark these points. Lay out the 1" x 1" grid at the tip of the strip and pencil in a smooth curve following the crossing points on the grid diagram and joining up with the leading and trailing arc points.

Use the saw of your choice to cut out the faired tip of the two "matched" and clamped together center strips. Shape and sand the edges to the fair curve. Repeat this process on the rest of the matched strip sets.

You now have two halves of the daggerboard. You need to separate them into two "MATCHED" sets that are "MIRROR" images of each other. I can't stress this enough. Be careful or you could epoxy up the sets and end up with two left feet/halves. Look at how I have arranged and marked the mirror image sets.

To make it easier to assemble the strips, do only one half of the daggerboard at a time and place the other mirror image set somewhere out of the way.

Take each of the cut pieces and stack them in position (widest on the bottom) according to the dimensions in the plans, and on a solid, flat surface. I use an old piece of 2x12 to act as my level base. The top ends of all the strips are even. The first two strips are even on their leading edges. The next strip set back 1" from the leading edge. The top strip is set back 1" from the front edge to the strip under it. Look at the cross section drawing to see the relationship of all the strips that make up the framework of the foil.

To keep the stacked strips from moving about while you epoxy them together later, drill four holes on the lengthwise centerline of the 2" strip and equally spaced down it's length; and drilling into the flat surface you are using underneath (2x12). Make sure that the stacked strips are still in alignment. Use a drill bit that is the same diameter as any small finishing nail you have laying around the shop. Push a nail into each of the drill holes (and into the 2x12) and remove any clamps.

Take a pencil and mark the outline of each strip on the one below it. This will give you a reference of how far to spread the laminating epoxy. You will coat the rest of the strip and the edges later before you spread on the EZ-Fillet. Less exposed epoxy, less chance of getting it on you.

Pull the nails and set the top three strips aside. You will want to place some plastic sheeting under the first strip to protect your work area. Take the first (biggest) strip and line it up with the nail holes in your backing board and insert the nails through it, the plastic, and seated in the bottom of their holes in the 2x12. Do this now or it gets sticky if you wait until the strips are coated with epoxy. It's ok to coat close to the nails with a layer of epoxy as you build the stack; just don't leave a big puddle. The SilverTip epoxy will not stick to the nails, but you may need to use a hammer to get them out again.

Coat both the "top" of the first layer, and the “bottom” of the second layer with a good thickness of epoxy. I don't use the rubber squeegee for spreading the epoxy on these strips. It spreads it too thin for a good lamination layer. I use one of my old plastic squeegee's that is a little rough along the working edge. That way I leave more behind. I coat one strip, and then do the other, and then come back and give the first one another coat. I find it leaves me with an epoxy coating of the correct thickness that's not too dry or with excessive squeeze out.

When you place the second strip on top of the first strip; pull the “top” nail and place it through the top hole in the second strip. The first strip is still held in place by the other two nails and it won't move around on you. That way you don't have to go poking around trying to find the hole in the plastic and the backing board. As you rotate the second strip around to line up with the first; you can pull the other two nails. Just make sure you also keep the first strip from rotating, as you line up the second strip and replace the two nails. Repeat this by coating the top of the second layer and the bottom of the third and place in the stack. Repeat with the top of the third and the bottom of the forth strip. Check to see that the strips are all laying flat, with no warps and replace the nails with sheet rock screws and just snug them tight. Cover with some plastic sheeting and place something with enough weight to keep everything flat on the wider trailing edge part of the daggerboard. If you have an edge that wants to lift, just use a short sheet rock screw to hold it down. The fillet material you use later will cover the holes. Let the assembly cure overnight.

Note: Remember the second stack is a Mirror Image; is laid out backwards and requires it's own set of nail guide holes. Stack this set and drill new holes as before.

Repeat the process with the other set of strips, but in a mirror image of the first. Everything is done the same again as before and let this set cure overnight.

After the two mirror image sets have cured, it's time to join them up. Coat the bottoms of the two stack sets with epoxy, line them up with new holes for the nails or screws (the old ones from the first set will not match up), and lightly clamp (protect the clamps with sheet plastic) the edges all around. Let cure overnight.

Repeat everything we have just done with the daggerboard for the assembly of the rudder pieces into mirror image sections and epoxy the halves together. The measurements are different, but the construction is the same. Only the center six pieces meet at the rudder head to give a ¾" thickness overall.

Now you have the two halves of the daggerboard and rudder laminated together to form their foil sections. You can now see what we have been trying to develop by looking down the foils from their ends. The stair steps have formed the outlines of the foil sections.

It's time now to take out the rasp and dress up the edges of the foils. Make sure to keep straight vertical lines on the leading and trailing edges and not ruin your good workmanship up to this point. Radius the corners; round and smooth the leading edge following the cross section outline drawing above. Just sand smooth the trailing edge.

The daggerboard and rudder foils have been cut, laminated, and smoothed to their “skeletal” shapes and now only need to be fleshed out with some wood filled epoxy fillet material.

This will conclude the basic construction part of the story and we will pick it up again in a couple of weeks for the filleting, fairing, and finishing out of the foil sections.

Thanks again for reading my stories.

Warren Messer
Red Barn Boats

Here is a downloadable PDF file with layout and measurements for constructing a complete rudder and daggerboard set. (click image to download PDF file)

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