WARNING: this particular transducer design is not intended to be installed on a real boat for safety reasons. The threads between the compression ring and the housing may be stripped following an underwater impact, causing massive ingress of water. This design is intended to be used only for development purposes on special floating devices.
A future improvement will be to modify the form of the yellow urethane matching layer so as to get rid of the recess. This first prototype will be used mainly to test the electronics outside of a real boat, so that the safety epoxy plug will not be cast for the moment, in order to keep full access to the transducer.
I was fortunate to get the help of a competent machine shop owner to achieve this. Here are some pictures.