Question
In 1980, my husband and I sailed from New Zealand to Hawaii and back.
Just the other day we confessed to each other that, on quiet nights in
the middle of the ocean when there was very little wind and hence very
little boat noise, we could hear voices coming from the mast. These
voices would be both male and female but you couldn't make out what
they were saying. We were both quite sober and were not under stress.
Can anyone explain this? Our mast is aluminium and the stays are made
of coiled wire.

Jenny Pollock , Nelson, New Zealand

Answers
The ghostly voices were from short-wave radio stations--possibly quite
a few of them overlapping. The mast and the rigging of a typical small
boat are just about the right size to resonate at the frequency of a
short-wave radio signal. If two items of metal are joined and there is
some corrosion between them, the junction will act as a diode and
"rectify" or demodulate the AM radio signal. This causes an
audio-frequency current to flow in the metal.

There are several mechanisms by which the audio-frequency signal could
be converted into sound waves, including causing vibration of the
rigging as the current interacts with the Earth's magnetic field.

Sam Mulholland , Bristol