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Thursday, April 05, 2007

In Search Of A Rudder (Part 2)

So, last week we picked up the rudder design from Bob Perry's office. This visit was a bit different as things were more easy going and we tangented on all sorts of topics after we discussed the rudder. But, Tristan went over the numbers he used with the design. I asked couple pointed questions about the new design in comparison to the original Westsail drawings, which he answered satisfactorily. Questions like how the forces will spread over the rudder, and where the rudder is to experience the most loads. Construction will be of stainless steel, foam, glass, vinyl ester resin and G-10 laminate. Without the big steel plate in the middle, it will be about half the weight of the original. It will also have a bit more surface area than the original.
Aesthetically, in profile, the elliptical trailing edge really compliments the canoe stern of the Westsail. Though one would only see this when she is out of the water. I think Bob's comment was "Yeah, but you will see it. Besides being strong, I like things to look nice." Ok, I can appreciate that.
Tristan also included rudder bearing size and construction recommendations. In particular, one of the self-aligning bearings from Jefa.
When we asked the guys "What makes this design so different, in comparison to the original rudder?" Bob came back and said "This rudder is engineered. The original, most likely, is NOT. Back then, they just guessed at a design, multiplied it by a safety factor, then threw it against the wall to see if it worked. That's how we did things back then. You guys probably have the first engineered rudder for this boat (Westsail 42)."
Remember, the Westsail comes from an era (early 1970s) when slide rules just started to vanish and pocket calculators were just emerging (WITHOUT scientific functions, mind you).
Anyways, we are starting the construction of the rudder. We will probably have the webbing plates CNC waterjet cut shortly. We are waiting on the foundry for the bronze casting of the rudder shoe. The foundry is pretty backed up with work right now (which is good for them as a lot of that type of work, especially production, is going overseas). We need the shoe to verify the real dimensions for the rudder frame before we have it assembled.

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