My 2000 H340 has an instrument cluster on the sea hood over the companionway. It has a Raymarine/Autohelm ST30 Depth and ST30 Speed display linked to an ST60 Wind Display. This summer, the ST30 speedo stopped working. I could run through all of the functions on the display but got no speed data. I removed, cleaned and replaced the wires on the back of the unit but it still would not work. Here are some of the transponder troubleshooting strategies recommended by Raymarine: 1) Make sure the paddle-wheel spins freely and is not fouled. 2) The transducer may become infiltrated by water and should be pulled an allowed to dry out 24+ hours then tested by spinning the paddle-wheel. 3) The arms of the paddle-wheel may lose their magnetism and can be tested by seeing if they are attracted to an iron screwdriver. 4) Power down the instrument, Disconnect the GREEN and the bare SHIELD wires from the back of the display. Connect a multi-meter to the green and shield wires and set the multi-meter to continuity/resistance (ohms). Slowly rotate the paddle-wheel. As the wheel is rotated, the multi-meter should alternate between an open and closed circuit. One complete rotation of the wheel should open and close the circuit four times. If no open or closed circuits are detected upon rotation, the transducer has failed and should be replaced.
Raymarine no longer supports theST30 instruments but I found that an Airmar replacement transducer, Raymarine #E26031 – 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 also has the ability to measure water temperature but that function is not supported by the ST30 display. If the display also fails, Raymarine says that their ST40 display will work with the old of 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.

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.