Mounting a Depth Sounder Transducer In Hull - Keith Merkley

This image shows the method of mounting a depth sounder transducer in the hull so as to avoid drilling a large hole in the hull. The diagram is from a Seafarer manual and I have used this method successfully. There is no explanation of why castor oil should be used but it is a very light oil and is available from a pharmacy for a couple of dollars as only a small bottle is needed.