The rudder to hull topic has been going around lately and I figured I'd start my own thread since I too have continuity from my rudders to the hull.
History is 1986, 32' Sedan with dual helm, cable steering. From the previous owner logs there is no record of the rudder bearings ever being changed but cant be certain about that.

With closed circuit between the rudder and hull I decided to pull off the rudder parts 1 by 1.
When sitting back there looking at the transom on your left is just the rudder post and arm with link bar to other rudder. Nothing special.
On your right is the post, arm plus the dual helm assembly.
You have the top most cable which looks like a throttle cable that goes back to lower helm to engage upper or lower station. Under that plate are the 2 larger steering cables.
I decided to remove the bottom plate first and test. Pulled the pin out and separated one of the steering cables from the rudders.
Tested rudder arm/post to hull, complete isolation. With the meter leads stuck to rudder arm/post & hull I touched the separated steering cable to the rudder arm and I was shorted to the hull, meter beeped.
I got lucky on removing the problem part on the first attempt.
However, that problem steering cable is fastened to a piece of vertical plate which is mounted right behind the port fuel tank. Both steering cables have a type of universal knuckle that allows them to swivel. These knuckles are mounted through that plate via castle nuts and split pins (cotter pins). Its a PIA to get to these as they are so close to the fuel tank but it is possible.
I removed the lower steering cable knuckle and repeated my continuity test, short to the hull, meter beeped.
That tells me the problem is somewhere up along that steering cable.

Anyone with a lower helm knows the steering cable (which is jacketed/insulated in plastic) connects to the chrome steering hub via the wooden or black vinyl covered helm. There is no metal involved on that end of the steering. So I'm fairly certain the lower cable arm which is shorting out does NOT go to the lower helm.
I'm assuming it runs up to the bridge and everyone with a bridge (except for Jeff ) knows that chrome hub is fastened right through the Aluminum instrument panel. Unless that steering cable is chafed to the point of making connection somewhere along the cable run, I'm betting a cold brew the reason the rudders are shorted to the hull is because the steering cable is in contact with the metal steering hub which is in contact with the Aluminum instrument panel. And I'll bet that is why Jeff told me sometime ago that his rudders are isolated from the hull. You remove the bridge, and you remove the hub connection to the hull.
With that long winded theory I'm going to remove the hub and retest plus I have to find a way to isolate the knuckle behind the fuel tank. I will say the other knuckle for the lower helm cable is also connected to that Aluminum plate and is NOT shorting to the hull. Marinette did use some hard plastic on the castle nut side and rubber on the knuckle side but I disturbed everything when taking it apart so I'll probably never get it isolated properly. Will need to get something similar to the prop shaft bolt isolators.

Hope this helps anyone else trying to track down rudder isolation problems. This is obviously not the solution for everyone but if you have cable steering a metal wheel hub and a bridge, this may shed a little light on the subject.

-Karl

So that means steering cables and control arms are all touching the hull via the wheel hub except for the rudder posts due to the isolation materials?

I didn't really see how any isolation material could fit around the square shaft. Looked like tight tolerances but I'll take a closer look and take some pictures too.

Was also thinking perhaps my wheel hub on the bridge is defective. Maybe by default the hubs are isolated from the boat??

Thanks for the info,
Karl

Nice pics.
Did your boat initially come with isolator material on the rudder posts??

I'm wondering if Marinette isolated the rudders at the factory or if they just let them short to the hull. I dont know why they would do that when they islolate the shaft unless the props have a higher chance of electrolysis over the steel rudders.

Curious if others have isolated rudder posts.

Thanks for the pics,
Karl

I checked today and it looks like I too have 2 little pieces of angle iron in there. Probably Aluminum. I didn't have time to really inspect. I don't think its plastic.
I'm starting to wonder if the rudders were never intended to be isolated. Really curious what other people have. Original owners would be the best. Who knows what the previous owners did or had done.

It looks like there is a black plastic disk fastened to the underside of the arms but I cant really tell until I get down there with flashlight.

-Karl

I pulled my rudder and found there is a cutlass bearing that should be isolated from the hull. There is a plastic stuffing box with what looked like graphite packing? a conductor? The steering cable is bolted to the hull direct, and the rudder arm, brass, is directly bolted to the rudder stock. I feel the system may be a source of a fault.