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Rudders and Centerboards for Dinghies and small Boats: Construction: Materials: Meranti, Philippine Mahagoni,  any straight grained timber that glues and machines well. Profile: Rudders turn and require a profile that can handle larger angles of attack without stalling. NACA 0012 has the lowest drag and greatest angle of attack before stall. Dinghy rudders made from laminated planed 22mm timber need a cord length of 176mm to have 12% thickness/cord length ratio, which fits in with most smaller boats. Centerboards and dagger boards on the other hand operate at much smaller angles of attack and could use a NACA 0010 profile. This works fine if the board is no wider than 210mm. Any larger chord lengths will require a thicker foil to stay around the 10% ratio. The other approach is to stay with 22mm planed timber for the boards too, but use a profile developed/advocated by Neil Pollock. Basically this consists of a leading edge portion similar to the 10-12% NACA profile, followed by a parallel section ending in the trailing edge portion. The leading and trailing edge sections are always the same thickness / length ratio and the wider the board, the wider the parallel section gets. The benefits of this profile seem to be that for the low thickness ratios that we are interested in, which tend to be 6% and less for daggerboards and centerboards, they can handle slightly higher angles of attack without stalling. For low angles of attack, lift is apparently about the same for most foils, but the sharper leading edges of say a NACA 0006 stall sooner. Furthermore, trailing edges being long and thin are more prone to damage. A practical benefit of the parallel section is that they are stronger as there is more material in the right place for strength. Good for the sailor standing on them to right the dinghy after a capsize. Making up a rudder or dagger/centerboard Both rudder and daggerboards are laminated using planed 44x22 (7/8”x13/4”) stock. Cut the required number and length of pieces then glue them together with epoxy glue mix. Use carpenters clamps or if not available you can make up some simple clamps by cutting some pine stock a little longer than the width of the board. Screw end blocks of similar timber across on either end and use matched wedges to supply the pressure required. Whichever clamping method you use put wax paper between the clamps and the laminate so it does not stick to the clamps. When the glue has set plane by hand, but only the high spots, to loose the minimum of thickness. Thereafter mark out the outline shape, cut it out, plane and sand the cut edges square. The profile shape is approached by chamfers that are tangential to the final shape. Working from the drawing, mark out the lines that describe the chamfers that are required. You can plane the chamfers, but if you have a small angle grinder fit a #40 grit soft disc, put on a mask and grind the chamfers to the lines. This is a surprisingly quick way to remove the excess wood. Tidy up with a hand plane to further break the edges the chamfers create and then round by sanding with a block backed production paper. The leading edge radius must be nice and even and the trailing edges are squared off. Updated: 05 June 2011 Back to Tips and Hints menu

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