My rudder has two hole in it through which a pin is place to hold the rudder in place at two different positions.  One is 3 inches from the top, the other is 32 inches from the top (the top being defined here as the bottom of the bulge at the top of the rudder that rests on the bracket when there is no pin in place?

Does anyone have more than one hole?  I ask this because I have heard reference to a shallow water position for the rudder.  Where my bottom hole is located would pretty much keep the rudder out of the water altogether.

I am talking with a boatyard in Thailand where I live part of the year about making me a new rudder.  I have prepared some rudimentary google sketchup drawings that contain the dimensions of my rudder, along with some photographs.  I will post these when I am finished with the process.

My boat has two holes in the rudder.  You can see it in the photo here:
http://www.d.umn.edu/~jrichar4/boat/DSC_0539.JPG

I would be careful with HDPE as it is quite heavy at thickness.  Plus it can be hard to bond epoxy to it unless flame treated. 

I helped a friend make a keel with a 7' draft years ago.  We used a large laminated beam and shaped the foil with a router that rode on foil shaped guides.  The router ran top to bottom and hogged out the foil shape.  From there we faired and glassed the end result. He ended up smelting his own keel bulb in the dirt using lead.

You could use foam in this case provided you encapsulate the foil with fiberglass using a vacum pump.  Another option is balsa or balsa and plywood provided you take care where you poke any holes in the end result to protect from water infiltration. 

I have had to purchase some glass and core in small quantities from these guys:
http://www.expresscomposites.com

Ask for Jim, he is nerdy and may offer some additional ideas.

-Josh
Dawson 26