Looks like the back cover for bulkhead mounted electronics
. Notice it has a sleeve for a wire. I had older data marine depth
that had these mounted inside on the bulkhead to help dress out the business end. Ritchie NC-20 Navigator Bulkhead back cover
Something like this maybe
Manufacturer: Ritchie Compass
Manufacturer Part No: Nc-20
this page to a friend
Navigator Bulkhead back cover for model no. BN-202.