Don't worry about the heating
. A marine radio
only puts out 150 watts maximum, at a nominal output impedance of 50 ohms, that's a PEAK current
of about 1.4 amps.
When you feed the bottom end of a long-wire antenna
, the bottom is a high voltage point. Depending on the frequency and the wire length, the voltage can get quite high. The fiberglass
might be a good insulator when dry, but when the deck
is wet with salt water
probably not so good. If the bottom ends of the wires aren't insulated, then you certainly don't want to touch them when transmitting.
With all of those caveats, there is nothing to prevent you from feeding the antenna
at the chainplate and seeing what happens. There is one more option that I used years ago and not on a sailboat. You would connect the antenna output of the tuner to one side of the split backstay, the ground terminal of the tuner to the other side of the split backstay and to ground. If you are lucky and the lengths are right, it will work. Google
the term "shunt-fed long-wire antenna."
I wouldn't think that connecting the tuner BELOW the tensioner would work since the tensioner doesn't have a good connection from one end to the other.