It looks to me to be a high amp, 12 volt power point. It has 2 notches in the socket (probably different sizes to orient polarity) and threads around the socket to screw in the male plug. Have you checked to see if it has power to it? As suggested, if it's near the helm, it was most likely the power connection for a wheel pilot, so look for a breaker on your panel.
I've never seen one exactly like that, but it might be nice to replace it with a new one to power a cockpit light or computer converter, etc.
It is a old type 12 volt power socket.
They normally came with a screw on lid and a plug with two contacts at the bottom.
The plug can only be inserted on way because the plug has got an alignment pin at the side matching a groove inside the socket.
I replaced a similar socket from 1978 this summer..