Fast Blades  
By Alan S. Glos - Cazenovia, New York - USA

I grew up racing small one-design dinghies (Rhodes Bantams, Lightnings, Penguins, Thistles and the like) and given the strict one-design requirements for these boats, there was not much one could do to make one boat faster than another. However there was usually some wiggle room in the shape and construction of rudders. In one-design rudder designs there was usually a maximum thickness requirement that was checked by a template at regional and national regattas but other than this thickness requirement and the two dimensional shape of the blade, there was often quite a bit of latitude in the actual cross sectional shape of the rudder blade itself. Hence rudder shape and construction was fertile ground for eking out a little more speed.

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If the maximum thickness for a dinghy rudder is, say, 7/8”, one could find an appropriate board, plane it down to 7/8”, cut out the prescribed shape, hang pintles and tiller fittings on it, slap it on to the stern of the boat and go sailing.

Let’s start with some basic observations. If the maximum thickness for a dinghy rudder is, say, 7/8”, one could find an appropriate board, plane it down to 7/8”, cut out the prescribed shape, hang pintles and tiller fittings on it, slap it on to the stern of the boat and go sailing. Even with the squared edges, it would work, but with all the turbulence and drag, it would be deadly slow. A better solution would be to shape the underwater portion of the rudder blade into a proper hydrofoil by rounding the leading edge and tapering it off to the trailing edge allowing the water to move over the foil with the minimum of drag, back eddies and turbulence. To make the design considerations even more complex, the rudder must perform well at all angles of attack as the rudder is moved along its axis when the skipper steers the boat over the race course. It didn’t take long to conclude that there were an infinite number of shapes one could carve into the blank, but only one of them was the best shape. A trip to the local library yielded a few books on hydrodynamics, and the image that stuck with me was an overhead photo of a trout with a fairly blunt head (leading edge), maximum thickness about 1/3rd of the way aft of the leading edge and a smooth taper leading to a fairly sharp tail (trailing edge.) There was a lot of other scientific jargon mentioned about laminar flow separation, coefficients of drag etc. but it was the image of the trout cross section that stuck with me. God don’t make no slow fish, so “trout shape” was clearly the way to go.

My first attempt at making a racing rudder was a Penguin rudder for a friend who raced at a local lake. He had an old boat, and his rudder was damaged. Knowing my interest, he purchased a beautiful piece of Philippine mahogany, and got me a set of the official plans from Philip Rhodes Naval Architects, the designer. I was a high school student at the time, and usually took a wood shop class in lieu of an end-of-the-school day study hall, and I was always looking for projects.

The plans were very specific about the shape, and after planning the board down to maximum thickness allowed, I made a full size template, transferred it to the plank and cut out a blank on the bandsaw. I then scribed a center line on the edge of the blank using a depth/marking gauge, and per the plans, made a grid on the blank. Using this grid, I scribed a maximum thickness line down the face of the blank on both sides and then penciled in several stations that would later be used to check the cross sectional shape. I then constructed a set of sheet metal shape templates from the plans that corresponded to the several stations on the blank.

The next step was the hard one; carving the desired shape into the blank. There is story about the man who approached a master sculpture and asked him how he carved a statue of a horse from a block or marble. The artist responded: “It’s easy – just cut away anything that doesn’t look like a horse.” Hence, my task was to simply cut away anything that didn’t look like the desired rudder shape.

My shop teacher, Mr. Nelson, told me that using a hand plane was the best method to rough out the shape. The planes in the shop were old and dull, and my first task was to grind a proper cutting angle on one of the plane irons and then hand sharpen it with a flat sharpening stone and cutting oil. I recall the process took the better part of three hours, but the result was a sharp plane that could shave a thin ribbon of mahogany without gouging or making burrs. I must admit that I became enthralled with the romance of using a sharp tool on a fine piece of wood.

Over the next few weeks, I slowly planed the blank down on what amounted to four sides, the two leading edges on each side (from the center of the leading edge aft to the maximum thickness point) and the two trailing edges on each side (from the maximum thickness point to the trailing edge center line.) I set the plane to shave off only a fraction of an inch at a time, maybe 1/32nd “ at a pass, and I checked the shapes frequently with the sheet metal templates that I had made from the plans. When I finally got done rough shaping and the templates matched, I switched to sandpaper, starting with 100 grit and working up to 220 grit. As good a tool as a sharp plane is, it still makes flat cuts with each pass, and the sandpaper rounds out the surface into a continuous curve. Mr. Nelson often said: “Don’t forget that sandpaper is a tool” and even though we had a power sander in the shop, he made us do most of our sanding by hand. I sanded for days, and when I was done, the results were gratifying and the unfinished rudder blade looked great. The only problem was that in my zeal to achieve a perfectly smooth surface, I had sanded too much and the maximum thickness ended up about 1/8th inch under the desired specification. It was still a nice rudder and a big improvement over the original, but in retrospect, I should have rough shaped the rudder a bit “proud” (i.e. oversized) and then sanded it down to specification. Yep, sandpaper is indeed a tool – lesson learned.

My next project was a Rhodes Bantam kick-up rudder for my own boat, and this time I did away with the templates and tried to eyeball the shape as best I could. Like the scene in the first Star Wars movie where Luke Skywalker goes on manual attacking the Death Star, I decided to ‘go with the Force’ and see if I could come up with a fast blade by eye. Working without templates made getting a fast, symmetrical shape a bit more of a challenge and required looking down the length of the blade often and then touching up here and there to get the desired end result. It was a good project but with the necessity of having to use 3/16” aluminum plate for the rudder cheeks, it came out heavy and useful only for off-the-beach cruising, not racing. Still the shape was a big improvement over the stock rudder that came with the boat from the Gibbs Boat Company.

About this time I read an article in a sailing magazine by Mark Lindsay. Mark had and continues to have the reputation of being the best rudder carver east of the Mississippi. The article showed how to build a small boat rudder from laminated 1” by 1” Sitka spruce strips, and the result would be a very light, stiff, racing grade rudder. I had to travel an hour to buy clear Sitka spruce stock, but I did find some and ripped it to the 1” by 1” specs, and then, following Lindsay’s instructions, I rotated each strip 90 degrees to change the grain angle for added stiffness and anti-warping and I also built a glue jig to hold the strips in alignment for edge gluing. Last, I threw in one strip of mahogany just for color contrast and a little more stiffness in the middle of the blade. Modern epoxy resin for amateur use was still a few years off, so I used Elmers brand waterproof resorcinol glue that was mixed from a brown liquid and powder catalyst. I didn’t have proper clamps, and ended up stacking cement blocks on the top of the gluing jig, but with a nice even run-out of the goopy glue, I figured I got a strong, even glue joint. When the glue cured, I scraped off the excess glue and rough belt-sanded the resulting blank and then convinced a local mill works to run it through a surface planer to get an even 7/8” thick laminated plank. From then on, it was simply a matter of band sawing out a rudder shaped blank, and planning and sanding it to shape. With all the different grain exposures, having a very sharp plane was imperative, and I recall pausing often in the shaping process to re-sharpen the plane iron. Mark Lindsay said a little judicious belt sanding was allowed, but I was too cautious and opted for hand sanding the final shape. This time I also intentionally made the blade a little under the maximum thickness as I planned on fiberglassing the underwater section of the blade for added strength and smoothness. When the shaping and sanding was complete, I hung the rudder sideways with the blunt leading edge at the top and covered the entire underwater section with one piece of lightweight fiberglass cloth draped over the blade and then wetted out the cloth with catalyzed polyester resin. When it cured, I trimmed off the excess fiberglass cloth, sanded the glassed blade and recoated with a flow coat of resin. After sanding again, I re-coated with a second resin flow coat the then got serious with finer and finer grits of sandpaper ending up with 600 grit wet-or-dry paper used wet. I finished the project with ¼” mahogany plywood cheeks (per the plans) and new stainless steel pintles. The laminated spruce and mahogany showed clearly through the fiberglass covering, and it carved through the water with a minimum of fuss and turbulence. [Author’s note: A few years later while refinishing this blade, I wondered if I could lighten it by removing the 1/4” plywood rudder cheeks. File this idea under “bad ideas” as it cracked end to end the first time I sailed the boat in heavy air. I keep the cracked blade around to remind me that good naval architects know what they are doing most of the time and we amateurs usually don’t. –asg]

Several years later while a graduate student in North Carolina, I met a young couple who were building a Rhodes Bantam from a kit from the now defunct Bay Craft Boat Company in Bay City, Michigan. The rudder that came with the kit was a single blank of Philippine mahogany but not shaped. We struck up a friendship, and I ended up volunteering to do the basic shaping of the rudder and did so in a single night at their married student apartment at Duke University. I didn’t even own a plane at the time and ended up buying a cast iron Stanley plane from a local hardware store, a tool that I have used and enjoyed countless times since. The rudder came out pretty good for a one night effort.

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I ended up building not one but two Sitka spruce rudders using WEST resin for the lamination gluing and coating. These were my best efforts to date, and although I did not dispense with the plywood cheeks, I did drill the cheeks full of lightening holes and both rudders are still going strong years later.

In the mid-1970’s I bought a new, second hand Rhodes Bantam that I planned to race, and the heavy plywood mahogany rudder that came with the boat had to go. By this time, WEST epoxy resin was readily available, and I ended up building not one but two Sitka spruce rudders using WEST resin for the lamination gluing and coating. These were my best efforts to date, and although I did not dispense with the plywood cheeks, I did drill the cheeks full of lightening holes (see photo) and both rudders are still going strong years later. The completed rudders went on my Rhodes Bantam, Spirit and a friend’s Amazin’ Grace, and both boats with these rudders on board won three Rhodes Bantam International Championships in subsequent years. I like to think that these homemade rudders had something to do with their success but even if they didn’t, they were great fun to build.

These days most of my spare time goes into small boat repair and restoration projects rather than new construction, but I still have a fascination with crafting fast blades. Just last summer I repaired a badly damaged Sunfish synthetic dagger board making a mold from an undamaged board and filling the mold with thickened epoxy (but that’s another story.) The technology has changed a bit over the years, but there is still no substitute for a sharp plane, a fine piece of wood and a good eye…and sandpaper; don’t forget the sandpaper.

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