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Systems:  Rudder Construction

 
Despite a brief dalliance with the thought of building a composite rudder, I eventually returned to the realities at hand and decided to build a new rudder of solid mahogany, build up from planks secured with waterproof adhesive and, as necessary, drift pins.

I took an old rudder shaft to my local prop and machine shop, along with some measurements I had made of the new, longer rudder tube, and worked out the final details with them, including the shape and size of the keyway at the top of the shaft, which was to mate with a solid bronze tiller head and strap from Spartan Marine.  After a couple weeks, the new shaft was ready; as of this writing, I had yet to pick it up from the shop.

With the original rudder in hand, I laid out four 1" thick mahogany boards, each about 6" wide and 6' long, from which to build the rudder blank.  I allowed ample excess length and width so that I could massage the shape of the rudder as desired.  I planned to change the original crescent shape somewhat, creating a more modern, squared-off design similar to those seen on most full-keel boats built by the late 60s.

After straightening both edges of all boards, I glued them together with resorcinol glue, and clamped them securely.  I set the blank aside and left it to cure for a few days while working on other projects.

Later, I unclamped the blank and, using the old crescent-shaped rudder as a template, traced out an approximate shape on the blank.  However, I changed the shape at the bottom end of the rudder, creating a straighter, more modern shape that flowed into the upper, curved shape of the original rudder at a tangent point about halfway up the back of the blade.

After much consideration, and a few changes to the angle at the bottom edge to ensure that the bottom was "kicked up" in relation to the bottom of the keel, I cut out the basic shape with a circular saw and a jig saw.


Next, I set up to rout a 1" cove in the leading edge of the rudder blade to accept the rudder shaft.  I had had a new shaft made of Tobin bronze, close in concept to the original but longer at the top end to accommodate the deck changes.  To partially recess the shaft in the leading edge of the rudder, I installed a 1" cove bit in my router, and attached a temporary stabilizing fence to the base plate with hot glue to help guide and hold the router on the narrow 1" thick rudder blank.



Then, in two passes, I routed out the cove to an appropriate depth of about half the thickness of the rudder shaft.


    


To strengthen the rudder and help hold the planks together, I decided to install several lengths of threaded rod through the blade.  Installation was a multi-step process.  First, I carefully drilled a 1/4" hole into the rudder from one edge, using a long bit that I had.  Once I had this pilot hole drilled, I enlarged it to 1/2" with a larger, long bit, bottoming out the bit to maximum depth.

To finish off the through holes, I returned the rudder over in the vice and repeated the process on the other side.  The result was not unlike the two teams that dug the Channel Tunnel, working independently from both sides and hoping to meet in the middle.  With minor adjustments, I was able to meet successfully.  I repeated this process for four threaded rods:  two that passed all the way through the rudder lengthwise, and two additional ones that dead-ended in the center of the rudder.

Next, I notched the rudder to accept some nuts and washers at the ends of the holes, and installed lengths of silicon bronze threaded rod in each hole, equipped with a nut and washer at each end.  After tightening the bolts, I taped over one side of the openings and filled the notches with epoxy filler, overfilling each hole somewhat so that I could sand it smooth later.

Click here to go on to shaping and installation.>


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