Commander 147

[ebb]

Pretty sharp.
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Was going to leave it at that.
But keep coming back to looking at that amazing rudder blade.
It's a translation, imco, right out of the test tank.
We can see the curves on the surface, as if the foil had just been tuned by a craftsman.

The techies did tilt the bottom up so it wouldn't crunch on the hard.

Years ago, looking up formulas for the foil, discovered that one shape rules them all.
One that all rudder shapers use. Or are definitely aware of. More or less.
A foil formula would work perfectly on a rectangular blade, which they aren't hardly ever.
So the rudder shaper is right back with his bronze & mahogany buddies......
he has to shape by EYE. Because the 'formula' infinitely changes on an non-rectangle blade.

Imco, getting the 12meter ready to win, designers would constantly, up to the race, be twiddling with the rudder.
Because it is an unknown, you have to work toward perfection - which we all know is unattainable......but let's keep trying.

Believe ledgendary surfboard shapers haven't got no stinkun formula: it's by eye. intuition, and feel.
Stick THAT in yor blinkin computer.

Do hold that shaping a rudder is in the realm of art.
Do hold that Alberg designed a foil shaped underbody into the Ariel/Commander, including the leading edge bulb entry.
So having the rudder profile as a foil is your call. It can be argued that board rudders with rounded trailing ends sailed just fine for 50 years.
On my composite constellate there will be a conservative 0012 aft foil profile leading to a fairly narrow blunt trailing edge with hard corners, no round.
Also will fill out the vertical profile to just inside the width of the keel. It's problematic but still the idea as to reduce drag and minimize eddys. It's also a more stable and more natural profile. One side of a board rudder is always cupped, imho.
Will stay within the aft two thirds of the NACA airfoil ordinates. No bulge, a sort of pumped up straight line.
google Keel hung rudders? http://www.boatdesign.net/forums/sai...ers-22016.html

Unlikely, but if your BS1088Meranti cups at all, Cut the opposing shapes so that the cupped sides get glued together. Might be kidding but don't think so!
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Art imitates Nature, and necessity is the mother of invention. Richard Franck

[Commander 147]

Well, I had to buy another sheet of BS1088 plywood for the rudder because the new shape was bigger than I had material to make if from. So I decided this weekend to use the first half piece I had previously made to make a template for the new pieces when my plywood gets here. I got the top of the rudder a little too close to the bottom of the hull because I still need to wrap everything in many layers of fiberglass so I will need to cut that down some to make my template accurate.

The bottom of this template slopes uphill at 13 degrees in addition to the lowest point being 2" above the bottom of the keel. That should keep the bottom out of the mud.

The other thing I did this weekend was build a jig so I could install the wood rails that the motor will mount to. I made and installed the rails and now I need to glass them in. Pictures below.