On Dec 9, 10:45*pm, Ned Simmons wrote:
On Tue, 9 Dec 2008 09:41:20 -0800 (PST), andy

wrote:

Is your approach based on ease of allignment or strength issues? *I
evision corrosion problems where the weld does not completely
penetrate the slot. *Upon typing this It is no worse (void penetration
wise) than my original approach with slotted shafts.

It sounds like you're concerned about crevice corrosion, and rightly
so. As long as your welds are sound and prevent water from entering
and stagnating in small cavities you'l be OK.

I don't know what the current thinking is on plate rudders. I built a
few large rudders about 25 years ago and I believe the design was
based on research from the University of Maine. There was fairing
added around the rudder post (it was the full length of the rudder), a
flange at the top and bottom, and a wedge cross-section at the
trailing edge. These modifications were supposed to decrease drag and
increase effectiveness without making the fabrication overly
complicated. If you're interested I can make a quick picture.

(Say hi to Rex for me if you see him. He doesn't answer my emails.
g)

--
Ned Simmons

I read an in-depth article in Professional Boatbuilder magazine about
rudder design. They talk about different foil types and effeciency
and all sorts of stuff. My original plan was to make a bronze
armature over which a white cedar core would be epoxied and faired to
a foil shape. Cover the whole lot with fiberglass, and you have a
rudder.

I have since spoken with a very knowlegeable gentleman from a
propeller shop in Portsmouth NH. He says that he works with a lot of
the racing lobsterboats from Maine. He tells me that the fastest
rudder is a flat plate and to not waste my time with the foil shape.
I also note that most of the boats that I see out of the water have
plate rudders. Now this is more Monkey-see-monkey-do than
engineering, but I am going to go with the real world experience
rather than the books this time.

Unless you can convice me otherwise.
Thanks again, and I will pass on a Hello to Rex.
-Andy