Rudder Post as SSB Ground?

[kish]

The HF SSB ground is totally dissimilar from a DC on board ground electricaly speaking.
https://en.wikipedia.org/wiki/Counte...(ground_system)

The SSB aerial radiates HF energy from the backstay and the SSB tuner, typically an ICOM AT140 tunes the backstay antenna for the frequency in use,
For efficient propagation the radiated signal needs a counterpoise, ideally matched to the radiated signal, for transmission efficiency.Tje HF ground is refered to as earth, but properly known a a counterpoise or m.re commonly a ground plane.

from the ICOM AT140 manual
"
The AT-140’s ground terminal MUST be connected to your ship’s ground. Grounding prevents electric shocks, interference to other equipment and otherproblems. Grounding also ensures effective signal transmission.

DANGER! NEVER connect the ground terminal to the following points. These connections may cause
an explosion or electric shocks:
– Gas or electrical pipe
– Fuel tank or oil-catch pan
IMPORTANT! The mounting plate is NOT con-
nected to the AT-140’s internal ground.
Ideal ground points

One of following points is ideal:
– External ground plate
– External copper screen
– External copper foil
Good ground points
If electrically connected to sea water, one of the fol-
lowing points is usable:
– Stainless steel stanchion
– Through mast
– Through hull
– Metal water tank

Undesirable ground points
AVOID the following points, if possible. These con-
nections may cause noise or electrolysis:
– Engine block
– Ship’s DC battery ground

Electrolysis
All ground cables from the AT-140, HF transceiver, etc. on your ship should be connected to only 1 ship’s
ground.
AVOID connection to 2 or more points. Voltage difference between 2 or more ship’s grounds may cause
electrolysis.

AVOID connection between dissimilar metals where
an electric current is present. These connections may cause electrolysis.

Counterpoise
If your ship is made of FRP, etc. and a good ship’s ground is not available, connect a counterpoise.
1⁄4λ(quarter wavelength) radial for each band is suit- able for a counterpoise. Install the counterpoise directly below the AT-140’s ground terminal.
Insulate the ends of each radial from other metal objects. Lay-out the radial horizontally and as straight as possible.
"

A manufacturer of a counterpoise, which does what ICOM recommend is the KISS-SSB link About Us

I have that unit installed and it works well.

[Brian.D]

One can make their own KISS. https://briandphoto.net/KISS-SSB.html