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 Building Rudders By Shaping Foam With Important Updates as of oct 11
 The profile for the rudders is represented by the drawing at right. The leading edge is slightly finer and the trailing edge is not to scale. Actual trailing edge is about 2-3 mm wide.  


The designer is notorious for drawing rudders that aren't big enough to work for low speed navigation but not long ago the mag Good Old Boat had a brilliant tech article (as they do) on rudder design which gave me the courage to wing it.

The dotted line indicates about the designed dimension. The rudder shaft position was also moved to balance the rudder.. hopefully. I talked to the skipper of another boat of similar design who after ten years of putting up with the smaller size, added the width as I have shown here but not the depth. Also he couldn't move the rudder shaft position. Even so his first sail produced a favourable result. He and his mate found much better response at the helm.



 This is PVC closed cell foam of 120 kg (means one cubic metre weights 120 kilograms). Very dense.

The designer offered to order me a set of carbon fibre rudder stocks and tubes, both arrived short of required length... OK... So, I used one of the handline stanchions that came along as well, and spliced it into the stock, about double what the correct extension would have been to accommodate the extra rudder size.

I cut the foam to fit the stock and buried in glue mix and....

   With the glue mix going firm and the leading edge ready to go...
   Filled the area and the leading edge part as well.
   Whatever works..

 Then I marked my profile bottom and...

UPDATE! Here is where I made mistake number 1. See the second line marking the trailing edge on the profile on the bottoms? That is where the trailing edge should have started and the leading edge should have been brought back accordingly. The rudder shaft centre should be about 17% back from the leading edge for best feel. Some racing boats prefer as little as 12% from the leading edge. My final shape comes out to about 19.8%. I asked Bob Burgess what he thought and upon siting them he reckons they are worth a try and I think he is right. If after sea trials I find the helm trying to "seek" her own course, I'll spend a day on the beach reshaping by bringing the lower half of the leading edge back toward the stock.

   top... and...
   using my 7 inch sander mounted with a very sharp 36 grit pad, cut to the lines as shown. This gave me a good reference point to work from. I used a normal wood saw to cut off the material that made the taper toward the bottom so now I have my outline all around. Part tracing what I had drawn on paper (top and bottom) and the edges pretty much freehand.
   another view..
   Then clamped it down and went at it.
   There is the rough shape.
   And then round off the corners for flow and to allow the glass to follow the contour.
   The trailing edge was left a bit blunt and now use a glue mix to build it up. when hard I ground it to match the contour.

 With the trailing edge shaped I can laminate without having to bring the cloth around the trailing edge and still be assured of a seal to the core material. Not that foam is as vulnerable as balsa but still better to do this way.

UPDATE # 2! Bill and Malcolm Salisbury caught this one (thanks you two!). I was depending on the roughly shaped filler around the rudder stock to keep everything together under torque load but the experts said, "not enough" and Bob Burgess agreed so... see photos on the modification at bottom of the page. Really easy anyway. Wish all my problems were as easy to fix

   450 gr DB (double bias) is easy to wet and flexible, but not tough enough so two layers of it. Gift wrapping experience helps here. Making tidy folds is important. The top and bottom have 8 layers of the glass after the folding process. If it resists folding and laying down, just let it go a little gel and sticky and then try it but must get any air out!
   This was a hot day so very exciting!
   When the resin as going firm, lay on the bog...
   This is the pair sanded off and ready to paint. The funny blue colour is because of the blue poly tarp that was overhead.

 The Following are updated photos of the repair to strengthen the rudders.
   First the matter of the rudder stock balance. If I had the stock about 5mm ahead it would be spot on but we'll see later.


 This is what can happen when you go borrowing tools from neightbours... I just asked for a long drill! I wasn't going for bloody oil! But beggars can't be choosers...

I drilled a half inch hole right through the leading edge and well past the stock and being very careful to keep alignment.

   Did one at an angle back to anchor more of the lower rudder.
   I happened to have some 14mm (9/16th) fibreglass rod. I undercut the area around the holes carefully to eliminate all the foam for about 3/8 inch (10mm) all round. I cut the rod so it would recess in an equal amount and inserted them after the next step. With the rudders at about a 45 degree angle, I filled the holes and the part of the stock that was involved, with resin thickened with cab-o-sil glue mix, dropped in the rods. Then with a thicker mix capped the holes, let set and .....
   That is what it looks like done.

 copyright 2010 The Coastal Passage