Twisted wires and ferrite cores help enough innthe industrial world that we use the a lot to prevent cross talk on our control wires and circuits. Having one end of a sheilded cable grounded also helps plenty. If the tranducer cable has a sheild the head unit should have it grounded already from the factory. A fella could use a Dc to Dc converter. Run 24 volts to the converter step down will step it down to 12 volts and should clean it up also.
The love for fishing is one of the best gifts you can pass along