Was it calibrated? Was it showing depth below keel, depth below transducer, depth of water, or some random, uncalibrated number? RTFM.
Then the yard owes you a haul and cleaning.
By the way all the spiffy stuff that the fishfinder does happens in software. The transducers are the same.
I read the F'ing manual... and the unit was calibrated to display the depth of water from the surface... Don't go making assumptions.
While I am sure that it was state of the art in '87, it was a complete POS in 2012, when I ripped it out. Back when I first bought the boat it would read 10.5, 10.7, 3.5, 3.2, 8.8, then 10.2. WTF was that? a fish? did I run aground?
Yes, I agree that the yard that stripped, barrier coated, and painted the bottom of my boat owed me a new transducer. But, I'd have a new transducer, with the same old POS depth sounder, and I would have to pick a fight to get it. Not worth the aggravation.
A fish finder is a FAR better tool because it shows you the depth, the bottom contour, and gives you a pretty good idea of what the bottom looks like... I installed the dual frequency transducer, which is far different from the old one, to shoot through the hull. It does not just show the user a number which may, or may not be accurate, as my old depth sounder did.