Rudder profile

[andyp]

Hi,

My Crusader came with a fairly new Sea Sure rudder and blade, not the lightest in the world and the blade looks (and feels) to big. Before I attack it with a saw and surform can anyone advise on the correct shape, at present its has conventional parallel lines with a square bottom. I plan to use the P & B rudder bag as a template, will this work?

Andy P N3353

ps new Alverbanks arrived on Christmas Eve and plan to do most of the Gill series next year, just need to lose some weight (both me and the boat) now

[Mikey C]

Yeah, can't go far wrong...

I dont think there is anyone on the planet who can advise you on the "correct" shape... all subject to interpretation!

[simon ballantine]

[mutt (Guest)]

Simons advice is good. Profili can be used to print out naca 12 sections
(which is the generally accepted x-sectional profile for a rudder/daggerboard/centreboard).

I would advocate using western red cedar as a core as its lighter than ply, easy to shape with a a hand plane, and I think stronger than a ply core (having had my ply rudder break 4 miles out at sea during hte burton cup race of 2001). Use the naca sections to check the shape of the x section every 10 cm down the rudder. Its easier than it sounds.

Its best to first chop the red ceder blank up longitudinally and then rotate every other length so that the grain is pointing in the opposite direction. Then glue all the sections back together. That prevents the rudder warping.  

Although flat ended rudders (in profile) are marginally worse than curved (I forget the exact mathematically name for the shape) the tip is much more resistant to grounding as you launch.

mutt
N3486