I would like your switch to control the power to a sonar 12v transducer aboard my boat

I am lookng at your single channel DC remote control switch to control the power to a sonar transducer (12V DC) aboard my boat. I would like for the switch to be "normally closed" so that the sonar transducer receives power when the relay is off. Is this possible?

It is possible. The receiver have three output terminals, two terminals are normally open, and two terminals are normally closed.

You can connect your device to the two terminals of normally closed.