when would a stainless rudder be preferable to a glass one? is it a matter of the speeds your boat will do?
I've got a glass rudder as well and asked the same question at some point. The answer I got was I could see an extra knot (or more) at cruise with the same rpm's.
They said to try to hold a bat or other thick item in the water vertically while cruising and then try to hold a knife. I never tried it, but I got the point.
I imagine there are other benefits. It's a much bigger ground plane for your bonding system, it would probably survive being hit by an object better, and it probably has higher resale value.
Eventually a glass rudder could begin to get play in it around the shaft. That wouldn't be good.
Anyway, thats what I was told. Ymmv. Experts will have more detail.