Making a New Sailboat Rudder

When the rudder on our vintage 1971 Ericson 32 sailboat developed deep cracks and lots of rusty stains, I knew we needed to replace it.  The easiest way would have been to order a custom built replacement from one of several speciality firms I found on-line.  Unfortunately, the easiest way was also the most expensive.  While researching rudder construction, I decided that I wanted to improve on the original design with the goal of a stronger blade.  One thing was clear, I didn't want to be out in heavy seas with a failed rudder.

A problem with a lot of cruising sailboats from the seventies is slowly rusting rudder frames.  To be fair, I doubt if many boat builders from that era expected these boats to still be going strong, as many are, after 4 or 5 decades.  Of course, my homemade replacement rudder is intended to be a "next generation" version, correcting weaknesses revealed over 40 years of service.  Why not just copy the original?  After all, it didn't actually fail; it only looked like it was about to fail!  I rationalised my design as easier to build as well as much stronger.  This is what the new internal stainless-steel frame looks like:

The fin shapes are seal welded to the heavy rudder post.  My idea was to fill between these plates with rigid foam and then fiberglass the resulting blade shape.  I put a 1/8" fin plate every 6" and that worked well to help keep the rudder symmetrical.  All I had to do to keep the shape nice was grind the foam down to the plates.  The fiberglass work was easy.  I used WEST epoxy resin to glue in the foam as well as to laminate the fiberglass cloth.  Since I had a roll of carbon fiber cloth, I used it for the final layer on both the leading and trailing edges.  I wanted the construction to be "bomb-proof" and, as you will find out, I unintentionally put this blade to the test.

I removed the old rudder and brought it home so I could make careful measurements.  However, I forgot to carefully measure the boat skeg, into which the blade must mate.  When I slide the replacement into the boat,   it fit but was too thick to allow the rudder to swing side to side as it must to turn the boat!  I brought the new rudder back home and trimmed the "extra" material off using my electric hacksaw.  After trimming, the new rudder fit the boat perfectly and swiveled back and forth just like the old one.

OK, I extended the blade on the new rudder as shown above.  The old profile is shown in red and this change adds tremendous strength over the original rudder.  Unfortunately, I forgot to worry about clearance for the folding propeller!  So after building, then trimming to fit, I could finally test the propeller clearance on a cold, clear Spring day in Ontario.  Cue the drum roll..... "Hey, the prop doesn't hit the rudder!!" I shouted. Foolishly thinking this was the end of the rudder story, I painted blue anti-fouling bottom paint on the new blade and got the rest of the sailboat ready for our Spring launch.

In retrospect, this picture clearly shows the problem I was about to discover.  The folding propeller rotates as it opens.  None of this dawned on me until it was pointed out by a fellow boat owner about 15 minutes before my scheduled Spring launch.  At our harbour, a dozen of us boat owners split the cost of hiring a crane operator to launch our boats.  My mistake was not spinning the prop while checking for interference.  Now I was stuck launching the boat with the prop problem.  One of the other boaters helpfully suggested that I bolt the prop in the open position, where it no longer hits the rudder blade.  Great idea except that I couldn't modify the propeller in 15 minutes.  "No problem," he says, "just remove the prop now and put it back on after the boat is in the water."  And so I removed the propeller moments before the crane lifted our boat off the land and place it gently into the water.  Back home, I drilled and tapped the bronze propeller blades into the open, unfolded position.  Now all I had to do is dive down about 18" and replace the propeller.

 Lake Huron is a wonderful fresh water lake, usually quite clear.  Our harbour seems to be one of the exceptions, with water about as clear as milk.  Some say it's the calcium carbonate that leaches out from the near by limestone shoals.  I knew it was going to be a murky dive as I was renting the scuba gear, but once I was in the water, I found zero visibility.  Also, it turns out that May isn't the warmest swimming month.  After a couple of tries, I was able to replace the modified rudder and pin it in place with two new cotter pins.  To finish up underwater, all I had to do was remove the tools I had clipped to the propeller shaft while I worked.  Damn if the skinny rope didn't get tangled in the carabiners.  "No problem," I thought, I'll just cut the cords with my Leatherman multi-tool which was tied to my fanny pack.  Damn again when the tool didn't cut the cord but just wedged into the cutting jaws of the plier-like tool.  Now I was effectively tied to the bottom of the boat and I tried not to panic!  My panic was short lived, as I had to only unbuckle the waist pack and surface, but for a second or two, it was a scare.  Finally a use for my dive knife!  Ironically, the one time I really needed it, I had neglected to strap it to my leg.  I surfaced, my wife passed me the knife and in a short time, all the cords were cut free and the job completed.

The new rudder feels great under sail and power.  We didn't notice any difference in speed while sailing with the prop forced open, blades churning the water.  All went well until I turned on the engine to motor into our slip.  Bang!!  Sometime either while sailing or motoring, the 1/4" bronze bolt I used to force the propeller open sheared off, allowing the propeller blades to now hit the new rudder.  This was a test of strength I never intended, though I would have predicted the heavy bronze propeller would chew a hole in the foam-cored rudder.  Instead, the bronze prop shattered and fell into the lake somewhere.  There was barely a mark on the new rudder!  Oh well, that old folding prop never did provide enough thrust.  We made a video of the project:

Copyright 2013 Paul Larsen