Test first!!!
I have a 79 ODay 28 and sm looking to install a Hawkeye depth sounder. The salesman said that if thehull is not cored, the in hull transducer will work fine. My question is how to tellurium the hull is solid fiberglass or wood cored?
I'm sure fellow owners will verify that your 79 O'day 28 is not cored. The Hawkeye's inhull transducer did not work in my O'day 39(admittedly a thicker hull). Read the instructions. You must first test locations in you boat (with the boat in the water). The customer service person said that the standard in hull transducer was far from a sure thing (intended for very thin hulls). The Hawkeye people are well prepared for this issue and suggested I use the existing thru hull transducer from a non functioning Raymarine unit. Worked like a charm.
Four important takeaway points:
Test in-hull transducers in the water and under sailing conditions (or at speed for power boats) before you do any cutting or installing.
Transducers are simple devices that make a click and then listen for it. I'm told there is very little that can go wrong with them . If your depth gauge is not working, it's most likely the display where the brains are. Check with the factory to see it your existing transducer will work with a low-cost in-dash readout like the Hawkeye.
Never cut/splice/ or shorten the lead to the transducer with out first consulting the factory or a service tech.
Never run with scissors.