Sunday, February 20, 2011


     Two of my goals for this boat are a dry bilge (at least, most of the time...) and an increase in efficiency over the factory original setup. The rudder installation plays a part in both.
     The original factory setup for the rudder installation is comprised of a rudder port that is through bolted into the hull, and through which the rudder is installed from the bottom. The top of the factory rudder port is threaded (2 3/16" x 11.5) to accept a packing gland and lock nut. Normal maintenance consists of periodically tightening the packing nut, and replacing the packing when necessary. Those of you who own these or similar boats know how difficult it can be to access this area on the boat - let's just say it is no picnic. So, I am removing the conventional packing, and replacing it with a lip seal arrangement from Tides Marine.

     As you can see, these thread down on the existing rudder port, using thread sealer and the original lock nut, and the rudder is then installed as usual. There is a UHMW bearing in the unit, with grooves machined in the interior surface to allow water into the bearing, to act as a lubricant. Above the bearing, a rugged, replaceable lip seal is secured by a stainless retaining ring. These are Type "J" rudder seals from Tides Marine, and a good amount of information is available on their website, I will detail the actual installation of these seals in an upcoming post. The final installation should provide for easier steering, reduced maintenance, and a dry bilge.
     As to the rudders themselves, my first task was to clean off the barnacles and corrosion. So, I masked off the rudder stock with electrical tape, and sandblasted the rudder blade. Once they were clean, I examined the rudders for damage or signs of impact. Fortunately, it appears they survived the previous owners without incident. However, I was not happy with the shape of the rudders themselves, in that the leading edge was too wide, irregularly shaped, and very rough. On slower, displacement speed vessels, the rudders are normally shaped to a close approximation of an airfoil or teardrop - a rounded, blunt leading edge tapering down to a fine, sharp trailing edge, akin to the shape of an airplane wing. However, on a planing powerboat, the foil shape results in a loss of water pressure on the rearward sections of the rudder when at speed, leading to a loss of control. In order to maintain water pressure along the entire length of the rudder, designers long ago realized that a wedge shaped rudder was superior. Wedge rudders employ a sharp leading edge, with an ever thickening cross section towards the trailing edge. The result is a rudder that maintains control at planing speeds.
     But, and there always seems to be a "but", the rudders on a production boat are installed in an "as cast" configuration. As such, the leading edge is both dull and irregular - contributing to drag and a loss of efficiency. In order to smooth and refine the shape of the rudders, and get a bit closer to the "ideal" shape for a wedge rudder, I spent a couple hours working on them with the grinder and various abrasive discs. The overall shape has not been changed, but I have removed irregularities and rough spots, and the leading edge has been smoothed and sharpened. See below:

     Note that the rudders are not sharpened to a knife edge - that would be too weak, and the first impact with floating debris would cause too much damage. I have simply smoothed and refined the shape to reduce drag, without a reduction in the overall strength of the rudder. The rudder stock itself has been cleaned and polished with 400 grit paper, to provide a good bearing and seal surface. My wife is coating both rudders with several coats of epoxy primer, and once that is complete, the steering system will go back in the boat. Stay tuned....


  1. I love theses articles but the projected area of the rudder seems so inconsequential compared with the drag of the hull is it really worth the work (and possible weakening) to work the metal?

  2. The strength of the rudder has not been compromised at all. I merely profiled and smoothed the leading edge, while the overall thickness of the rudder didn't change. Is it worth the work? Probably not, but I had some time on my hands that day......