Rudder & Daggerboard Foils
by Warren D. Messer - Seattle, Washington - USA

Constructing A NACA 0012 Rudder and
NACA 0010 Daggerboard Foils

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

Note: You can leave the strip edges untouched if you want to. After reviewing the posts from the last story and rechecking the drawings at a higher zoom rate in my design program; I can go either way on shaping the strip edges or not. From the drawings, the outer edges of the plywood strips do get a bit of shaping, but so slight that it is not worth the effort. Just make sure there are no rough edges that act as road turtles or potholes when you apply the EZ-Fillet material. A slight touch up on the strip edges can't hurt. You can skip the next paragraph if you want to.

Block up the daggerboard blank with scraps of 1/8” ply and use a longer sheet rock screw to hold it to the 2x12 so it doesn't wobble around. Use a plane or rasp to slightly bevel the leading and trailing "long" edges of the top strip (the 2” wide one) so it matches the cross section view in the plans. Sand the bevels even and smooth. Clean off all dust.

Coat all the surfaces of the foil you are working on with epoxy, and especially the edges, and let the epoxy soak in. This will fill up the porous edges and surface of the plywood strips and keep from starving the interface between the fillet material and the plywood. Let it set a few minutes before you apply the fillet material.

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Mix up and bag some EZ-Fillet material as you have seen me do in the Laura Bay construction story; or just scrape it out of the cup as you need it. Squeeze out a bead along one of the "stair steps" and use a small straight edge to fair the material into the gap between the adjoining stair step edges. After you have filled all the stair steps; take a longer and more flexible straight edge and pull the full width. Be careful on the curves. If the material is pulling up, stop. Smooth out the fillet material as best you can and let it cure. Limit creating any high spots you may have to sand later($$). You can come back after it has cured and fill any low spots with more EZ-Fillet or QuickFair. Let the fillet material cure overnight.

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click to enlarge

Rough sand with 60 grit to smooth down the surface and find any high or low spots. Wear A Dust Mask any time you are sanding epoxy! Sand down the high spots to bring them back to the designed outlines. If you did a good job with the fillet material, there should not be too many low spots to fill after the first sanding. I haven't done the perfect fillet job on a NACA foil yet, so I always have some craters, holes, and streaks to come back and fill. Clean off any dust that may have collected in the depressions and make sure you give the “holes” a bit of a roughing up too.

Now is the time to break out the QuickFair to fill in the voids on your sanded surface. Don't mix up too much at a time. Stick with 1-½ oz mixes [1oz part A (tan) and ½ oz part B (white)] for fairing the surface. If you did a reasonably good job with the fillet material, it won't take that much QuickFair to fill in the holes and you will be surprised at how far it goes. You may want to take your time here fairing out the surfaces of the daggerboard and rudder by doing it in a couple of applications with a good sanding between fully cured coats.

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click to enlarge

Now run your hand over the sanded surface to locate any major depressions and lightly mark their locations with a colored pencil. If you change the color of the pencil between each fairing compound application, you have a better idea of which spots really need to be filled this time.

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click to enlarge

Give your finial fairing coat a good sanding and remove all traces of dust with a damp cloth. Once again give the foils a good rubbing with your hand to detect any high or low spots. If it feels good to you now, call it quits. No use wasting anymore time and materials to make it Olympics class perfect. Anyway, it's now a lot more efficient than a plan old board shoved down the daggerboard trunk.

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click to enlarge

For the daggerboard, we still need to mark and cut out, the "lifting hand hole" and “stop ring”. The stop ring is a ¼” piece of plywood scrap cut and smoothed to a 3” diameter. The hand hole can be sized to fit your hand and is placed in the thickest part of the foil cross section. Give yourself at least 3/4” of wood to grab. Use a 1" drill to make the end cuts and a keyhole/jigsaw to open up the center. Round and smooth all edges.

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click to enlarge

The stop ring is placed 1/2” below the bottom of the hand hole and is centered at the “balance point” of the daggerboard. I use the ring as the “stop” to keep the daggerboard from dropping through the trunk slot, and as a pivot point for the daggerboard to rotate on as it gibes in the trunk on different tacks.

You can find the balance point by cutting out the hand hole first and then holding the daggerboard with one finger in the opening. Move the daggerboard along your finger until it remains vertical. Hold it close to something you know is vertical to use as a reference; as I am doing in the photo. Mark that point as the centerline of the stop ring.

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Drill the holes for the ¼" x 3" stop ring and use the keyhole/jigsaw to remove the wood between them. Clean up the edges until the stop ring fits and epoxy the finished and centered ring in place.

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click to enlarge

Give both foils a finial touch up with 150 grit, remove any dust from the surface with a damp cloth, and apply at least two individually cured coats of epoxy to the daggerboard. Make sure to coat the interior of the handle and the edges of the stop ring. Whether or not you fiberglass the daggerboard and rudder is up to you. The coats of paint, epoxy, fairing compound, and fillet material, are plenty tough enough by themselves.

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click to enlarge

After the epoxy has cured, give the foils another go over with the 150 grit before you apply 2-3 applications of a high quality marine enamel paint. Let everything cure for a couple of weeks before you put it to use; that way the paint has plenty of time to cure and achieve it's full hardness.

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click to enlarge

The daggerboard is finished, but the rudder still needs hardware added before it can be attached to the boat. Mounting the rudder is something I covered in the Laura Bay series of stories.

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The NACA0000 foils we have just made will make a big difference in the performance of your boat. When I'm cruising along in the Laura Bay pointing high, and I push the daggerboard from ¾ down to full down; the boat heads up several degrees as soon as I do it. If you don't want a gibing daggerboard, you only need to shape the amount of foil that sticks out the bottom of the boat. Just measure down from the top of the foil the depth of your daggerboard trunk and adjust the outer layers to full fore and aft width for that distance. Everything else is the same. If your foils need to be longer, just add the extra inches to the top of the measurements. You can only lengthen the foils, you cannot make them wider or thinner/thicker and still be correct for that 0000 series number.

I will be adding a third story to this series to explain how I use my design program with the NACA4gen numbers generator to make foils that suit the needs for the boat you are building or dreaming of.

Thanks again for reading my stories and I hope this makes building and sailing your boat more enjoyable.

Warren Messer
Red Barn Boats

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