Saralee’s New Rudder click here to read or make an observation about this  article
By Craig Gleason - Shalimar, Florida - USA

For some time I have been dissatisfied with the stock rudder specified for my Stevenson Vacationer. It seemed to require too much effort to control the boat. Weather helm it is called and it refers to the tendency of the boat to want to turn up into brisk winds unless heavy pressure is maintained on the helm. With wheel steering this is a double pain as the mechanical advantage of the tiller bar is not there and wheels are a bit more tiring to hold. Looking around for a “better way” my search led me to NACA Foils. They are hydrodynamic structures used for keels and rudders. They are shaped much like aircraft wings and provide lift due to the water flowing over the curved surface of the foil just as moving air does with airplane wings. Where aircraft wings are normally single sided; that is rounded on top and flatter on the bottom, rudder foils are double sided with each side providing lift as it is turned to face the flow of water when turning the boat. Photo 1 shows the overall shape of the foil. This contour continues from the bottom of the blade up to the rudder box.

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Photo 1, Rudder profile for a #12, low velocity foil.

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I couldn’t seem to center the profile in the viewfinder so that it didn’t look bent. The cord, the fore and aft width of the blade, tapers to a bit more than 1/8th inch. This should be closer to ¼” but it just sort of worked out this way.

The metal ring around the prop is a rudder guard. With the rudder in the up position and tightly turning to port, the rudder will come into contact with the prop blades unless the motor moves with the helm. This boat is too small for that kind of automatic protection so the guard saves the rudder and reminds me to turn the motor tiller a bit if a tighter turn is needed. I fixed the gouges in the old rudder a dozen times or more. Photo 2 shows the rudder guard to be a ¼ x 1” aluminum bar formed around a 2 gallon metal milk pail and bolted to the cavitation plate. There are other ways to attach something like this so look around on the Net for other ideas. I like this style as it also alerts me before the prop is running in the sand. The strap is a fail safe to keep the rudder from falling if I leave the nut off the rudder storage pin,,,, again.

Photo 2, Home made prop guard.

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My new rudder is larger than that specified by the Stevenson’s drawings for the Vacationer. Balanced rudders are normally used to counteract weather helm. While the lead ballast at the foot of Saralee’s mast helped trim out some of the excessive rudder pressure, heavy winds always brought it back with a vengeance. Some degree of weather helm is desired as a safety feature. A boat with weather helm will automatically turn into the wind and stop sailing if the rudder is released. This is a very good thing to have happen if you or another falls overboard. A balanced rudder is made by moving some of the effective surface ahead of the rudder pivot point. In the case of the Stevenson rudder designs any addition to the front of the rudder adds balance and reduces weather helm. This modification is applicable to any boat experiencing excessive weather helm or poor rudder performance.

Photo 3 shows the stock rudder with Lexan shims. The blade is constructed “as drawn” and the Lexan shims out the blade to rudder box play reducing the strain on the pivot bolt and keeps the blade plumb in the box. That fine looking white adhesive is 3M 4200.

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Photo 3, Stock Rudder Blade

Photos 3 and 4 show the relative difference in size between the stock rudder and the new foil. The rudder head is made “as drawn” to fit the existing rudder box; however, the box requires minor modification. The new blade is 14” wide with 3 inches more material on the leading edge of the blade. This brings the front edge below the pivot bolt seen above and about an inch under the keel. Paul Riccelli estimates this to be a 20% increase in balance over the old rudder. He cautions that percentages over 15 may cause poor control at slower speeds At it’s thickest the new blade is just short of twice as wide as the old blade so allowance for the rudder box clearance must be made. Photo 4 below shows the new blade ready to mount and test.

Photo 4, Finished Foil Rudder

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The NACA 0012 foil makes a very efficient low speed rudder and was recommended to me by Paul, Barry Payette, and some of the builders on the Trailer Sailors Board. These foils are not hard to make and provide a really cost effective performance enhancement for any of our boats. I started by downloading the shareware program NACA Generator. This easy to use program will ask you for the general parameters of your new rudder and generate a set of scaled points that define the contour of the blade. Just like laying out a keel or other large components the coordinates were transferred to a piece of thin stock that was previously marked with a 1” grid. The points were connected using a thin batten and the template rough cut on a band saw. The finish work to smooth the template was done with a file and sandpaper. Try to be exact but don’t worry about small variations. Photo 5 shows my template. It is actually longer than the blade on the after part to make it easier to hold while checking the work. You can measure and mark at the same time.

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Photo 5, Foil Template

I am sorry that I didn’t take any progress photos. I didn’t imagine I would be writing this article so just bear with me on the construction details.

Charlie Jones, a professional boat builder from the Trailer Sailor group recommended building my rudder as high aspect (longer for more control surface), and to leave the bottom squared as opposed to rounded.. At 6 or 7 knots the squared tip really doesn’t add any significant drag. Armed with the advice and counsel of my friends I went to Lowe’s for wood. Now normally I would get good Douglass Fir at a real lumber yard; but this project required one 16” and two 12” planks. Using fir, that gets real pricey real fast. Lowe’s had some very clear white pine 6’ shelving lumber that I had noticed previously so that was my material choice. I was even able to find three very clear quarter sawn pieces. The 16” plank was ripped to 14“and all three trimmed to rough length. The 12” pieces were epoxied to the larger center board to build up the required thickness. Remember the rudder head is just above the trailing edge of the blade on the Stevenson boats and the 12” boards are flushed up to the front. When everything was cured the fun began.

The extra thickness of the foil must be accommodated by both the rudder and the rudder box. Photo 6 shows how a rounded relief is machined onto the rudder cheeks. The aft end of the rudder box must be ground down to allow the cheeks to pass as the rudder is rotated up and down. The best way to get this right the first time is to locate and drill the pivot hole in the rudder head and use the pivot bolt to hold the rudder in position so you can mark the arc that the bottom of the rudder box will require to allow rotation. Use the “as drawn” locations for the holes in the rudder head to insure the rudder box stops are still correct. Use small wood shims if the stops need adjustment. Relieve the blade and grind the box to allow free movement. Removing the rudder box to the shop will expedite this process. The preceding described work is best done before you start the contouring process to save wear and tear on the finished surfaces. Now is the time to find the required thickness of the Lexan if required. Lexan is easily worked and will not become brittle in sunlight like plexi-glass.. With all this done it is time to shape the foil.

Photo 6, Foil and Rudder box with Lexan shims

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Now Oyster would take his magic grinder to this and have it done in a jiffy; but, I like planes. Always have. There are other tools that will suffice and some are much faster to use; however, the feel, smell, and sound of newly planed wood is emotional for me. So out came the planes and I started rough shaping the nose of the foil. Working from nose to trailing edge I shaped the contour of the foil with my planes, finish sanders, and yes, finally the right angle grinder. Work slowly and check your contour with the template often. I marked the high spots with a pencil and used a bloc plane or the sander to work them down. As you near the trailing edge you will find that the 12” boards do not completely fair to the trailing edge. I filled the small (- ¼”) step with epoxy and fairing compound. Using 80 grit sandpaper I broke all the sharp edges and gave it all a once over. Next I applied a seal coat of epoxy followed with 6oz glass and more epoxy. I used three good topcoats of resin and then epoxy fairing compound as required. Continue to check with the template here as you can change the contour while fairing and sanding. Small imperfections are what glazing putty is made for. Get it at your local body shop supply house. After a light sanding, a primer coat of Kills. It preceded the blue latex top coats. I use latex on the hull as she is trailer sailed and the latex will touch up with no tell-tale marks and lasts for years with little maintenance. Latex is a poor choice for the topsides as it tends to stay a bit soft and white takes stains easily. Photo 7 shows the completed rudder.

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Photo 7, The finished rudder and rudder box modification.

I have only had the boat out once since making the new foil so I don’t have a lot of test data or performance analysis to share. I can say that in 10 knot and less winds she handles like a dream. The excessive weather helm has been reduced greatly at these wind speeds and low wind speed performance did not seem to suffer. Tacking seems much easier now. For any given steering action the required rudder deflection has been greatly reduced. A friend gave me a wind speed indicator today so now I can make accurate wind speed measurements. This will help generate accurate performance data as opposed to the by guess and by gosh methods. Still, I will be out on the water enjoying my new rudder so don’t expect a full blown technical report! Happy building.

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