OK, here is my thinking on drag.
I should note that I am fully aware that my "barn door / commercial fishing
boat rudder" is not a hydrodynamic beauty. But the flip side is how many commercial
fishing boat rudders have you ever seen broken, compared to how many yacht rudders have you seen broken?
My max speed, like when the boat falls off the edge of the earth, is 7-kts. If we are doing 5-kts, which is pretty much our average speed over 30,000-miles, how much drag/lost of speed can possibly be occurring? Maybe 0.1 or 0.2 kts? 0.5 kts?
My rudder has maximum movement of something like +/- 25-degs (it is a Whitlock Cobra steering
system) and from what I have seen of the Autohelm
movement over all those miles is probably 95% of the time the rudder is moving less than 10-degs to keep the boat on course - probably more like 5-deg or less. So how much drag can be occurring at a 3 to 5-deg rudder angle 95% of the time? Not enough for me to care about.
I think the safety
aspects of the construction far outweigh 0.1 or 0.2 kts. Besides, when we change from a fixed 3-blade prop to a feathering 3-blade prop we gained between .5 to 1.0 kts (depending on wind
conditions), so I am still to the plus side.
As to using the rudder as our ground plate, I checked with a couple of local, knowledgeable certified SSB people and read the ICOM
book on grounding plates and they all said - basically - that it was the "surface area" of the metal mass that was the important thing, and that the surface being painted or covered did not effect the performance. ICOM
says that you can use your keel
as a grounding surface too.
I think most people don't use the keel as connecting the antenna
tuner to the keel would be a nightmare to do since you need a large surface area connector - ie something thin and flat - to make the connection. Usually 2 - 4 inch wide copper strips.
On mine I went to flexible woven copper grounding straps that are made for HAM radios set-ups. I used two that are 1-1/4" wide, so in effect each cable is 2-1/2" wide. Having 2 cables
, I get the 5" (see previous picture of my tuner and rudder post). Another advantage with the cables
is that they can be made with fitted ends so the attaching bolts fits and fastens well.
Anyways, right or wrong, that's my thinking. So far I am happy, it seems to be working well and I think the pluses outweigh the minuses. I am not interested in getting that last 0.001 knot
out of the boat, am happy with 5-kts and a comfortable safe ride.