Most manufacturers use a foam core and fiberglass clam shells for rudders and
centerboards.   Freezing and delaminating is always a concern if water gets
inside.    My rudder seems very stiff and heavy, I think Stan put a LOT of
glass in there (2002).  

I cracked my head a couple years ago.   (The rudder head as well).  Stan was
busy getting ready for a boat show and I didn't want to miss the rest of my
season.   I did a temporary repair with more 'starboard'.   Its the same
HDPE milk jugs are made out of, treated for UV resistance and intended for
various marine uses.  It will crack.

On the advice of another sailing forum I later upgraded the head with new
sheets out of G10 / FR 4.   This is the stuff computer circuit boards are
made out of.  I reused the pintles and raising mechanism from Stan's design.   
Its too expensive for production boats and there is a mask requirement for
cutting, so I understand why Stan doesn't use it.   It cuts with a common
scroll saw, an advantage over aluminum alloy.   Also my local machine shop
was scared to mess with a boat part and declined the job.  

I think I used 0.25" .  A materials engineer claimed it would be much
stiffer and stronger at half the thickness of starboard, but I didn't buy
the good stuff.    I notice now that if you check the 'strong' box on the
granger website the product I used disappears.    Being ignorant I bought
the cheapest but was disappointed.   Gorilla glue laminated a second layer
to the bottom six inches of the cheeks, which stiffened it up considerably.  
Spray-painting with autozone bumper paint provides UV protection.  
Apparently its a common Australian sailors' solution.    




-----
Alex Cole
S/V Lark
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Sent from: http://rhodes-22.1065344.n5.nabble.com/