I had a similar problem on my 2000 H340 but with my speed transducer many years ago. Raymarine no longer supports theST30 instruments but I found that an Airmar replacement transducer for ST30/ST60 will fit the old thru hull fitting and drive the ST30 display. I found a new transducer with a complete thru hull fitting and plug on the Internet for about $60. The new transducer fit exactly into the old thru hull fitting so I did not have to replace that. If the display also fails, Raymarine says that their ST40 display will work with the old or new transducer. Raymarine also suggested that I contact GEM Electronics Co., the maker of Airmar transducers at 803-693-0777 to get their recommendation on replacing the transducer.
BTW:I found it virtually impossible to route the wires from the new transducer up to the sea hood display without dismantling much of the boat. The Hunter factory left a few empty wire chase conduits on the boat with wire-pull lines in place. Nonetheless, getting the wires, undamaged, to and through these wire chase conduits was still a major operation even with the use of an electrician’s fish wire. Instead, I chose to splice the new transducer leads into the original wires from the old transducer and the speed data to the display seems to function normally.
