Is it possible to fit a new transducer in to an existing through hull fitting while the boat is afloat, if so how would I go about it. The boat is a Cheveton New Campaigner built in the early 1960's the hull is 25mm Mohogany.
Boat is irrelevant. Normally an echo sounder transducer is fixed through the planking with its own fitting - usually bronze. So the boat has to be out of the water. It is also possible to fit a transducer on the centreline through the forefoot using an extra long transducer. The echo sounder manufacturer will offer transducers suitable for wooden boats.