Ruddy rudders

[EASLOOP]

I am going to start on the project of building a new rudder for my East Anglian sloop.
I can source two lengths of oak, 12" wide x 2.5" thick by 10' long. Fastened together will produce a single plank of 24" wide from which I will cut out the rudder shape taken from the existing rudder. However, the below water rudder section needs to be tapered toward the trailing edge so as to reduce turbulence and, no doubt, weight.

With only DIY pwer tools including a planer, belt sander etc. how can I be sure to shape this section without going awry and ending up with an unbalanced uneven mess?

I would appreciate comments from anyone with ideas.

rgds
John (in Blighty)

[Harry Miller]

Here's one idea.
Draw contour lines on each side of the blank. If for example you want a thickness of 1.5 inch along one contour drill a series of half inch holes along the contour line from each side. Then you sand, plane or whatever until you reach the bottom of the holes. You then have removed 1 inch from your original 2.5 inches.

[LLaver]

Before you start removing any material be sure you have marked the centre line all around the edge of the piece.
make 1/2 templates at a series of intervals and use them to check progress as you go.
Or you could just do it by eye (but make sure you mark that centre line or you will be lost with no referance point)

Lee

[George Ray]

(0) Assume the rudder blank is straight/parallel sided and marked off with parallel station lines maybe 1/2" apart on both sides that are all parallel to the waterline/waterflow.

(1) Lay a 2x4 on it's side on the workbench and on the narrow edges (both sides) draw the curve (foil shape) you want. Make saw cuts just down to the lines and remove the waste, leaving a 3 1/2" wide pattern of the foil shape.

(2) Lay the pattern on side (a) of the blank at station line 'a1' and fasten the pattern to the blank with small screws.

(3) Use a skill saw with the blade depth set so that the bottom of the saw cut will be a fraction shy of the desired surface of the finished curve. You will have to rock the saw a bit to keep the deepest part of the blade/cut in contact wiht the pattern, if not there will be sport that are not cut to proper/final depth.

(4) Move the pattern to all the other station lines on both sides and repeat the cutting process.

Notes:
(A) The closer you make the station lines the less waste you have to remove suject the the constraint that when they are 1/4" apart the chunks just fall out when you touch them.
(B) The chunks/waste should NOT be removed untill all cuts are dome because the grooved but flat surface makes it easier to work on if you want to come back and make more cuts and when you turn it over to do the (b) side if the (a) side is curved because the waste has been removed the thing is all tippy/squirrley and hard to work on.
(C) This is a lot like Ian's McColgin's comment about his method of scarfing plywood where he makes the saw cuts/kerfs to guide the waste removal to final design surface:
http://www.woodenboat-ubb.com/vbulletin/upload/showthread.php?t=48957

**********
Question:
Should the grain be quarter sawn to prevent warping of the foil, hence rudders/centerboards often being builtup from smaller pieces and pinned?

[EASLOOP]

Thanks for the input. Good point re: quarter sawn. Might put the price up a bit. Food for thought.

Thanks
John