10 November, 2009

Building the better rudder

The original rudder built by Award Boats is not very hydrodynamic or well balanced. The basic shape is a plain flat board. At higher speeds the blade tends to flutter.  The further the blade is from the pivot axis, the higher is the load on the tiller. The newer Gloucester rudders are built parallel to the axis reducing the tiller loads.

The wooden rudder blade needs to be locked to keep it from kicking up. This required me to lean over the stern to loosen the screw. In the Chesapeake I sail through very shallow waters. I was always worried about breaking the rudder. Going back was inconvenient and unsafe.

At first I wanted to build a whole new foil shaped blade, with a balance section forward of the axis. The amount of time to do this and also the shape of the rudder head made this impractical.

I decided to modify the existing blade by moving the center of the blade closer to the axis. I plained the edges square and added a strip of mahogany to the leading edge using  biscuits and epoxy. With a belt sander I rounded the corners and shaped the profile.

I drew parallel lines with a marker on each side of the blade as a guide. A rudder foil shape has its widest section about a third from the leading edge. The front nose is rounded. The rear two-thirds is a straight taper. Using a plane and a belt sander I removed material evenly on both sides until a foil shape was achieved. This was more of a art than science. Once I had the shape I covered the blade with a layer of fiberglass cloth and faired using epoxy micro balloons. To assist in lifting, give the rudder some transverse strength and have a emergency step, I epoxied a cross brace. Made from a single strip of wood I cut out the middle and slipped it on to the rudder.

The blade lifting mechanism is a set of pulleys on each side of the blade. One side for lift and other for the lowering. The rollers came out of a old dishwasher that I just took out of my kitchen. The rope is a single loop to a cleat on the tiller.

I usually keep some pressure on the rudder lock screw. If I hit shallow water I can quickly raise and lower the blade without going aft. For more open water I tighten the screw. One nice benefit is that the new line acts like a carrying handle when removing and storing the rudder.

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