ST50 Plus Tridata display speed is 50% low

[hwturn]

I have a ST 50 plus tridata. Recently the boat speed reads about half of what the SOG (from GPS) reads. I have checked at slack tide and same problem. I just replaced the speed/temp transducer with a ST800 and same problem. I went through the ST 50 plus re-calibration (not as easy as you might think) numerous times and the cal factor was 2.5 which is higher than the allowable limit so it didn't store the cal factor or fix the issue. I am having basically the same issue with the new transducer as with the old one. I also have a Ray-marine C7 MFDU and i60 Wind right now everything is tied togeher so I am worried that swapping out for a newer i50 tridata will cost a lot and not fix the problem.
Thanks,

[Chuck - Raymarine - Moderator]

Welcome to the Raymarine Forum hwturn,

As you have inferred, the problem of low speed being reported following calibration may be rooted in the transducer or speed sensing instrument. Should you have
- replaced the speed/temp insert with a speed/temp insert of the correct length ... i.e. the speed/temp insert's paddlewheel extends slightly out of the transducer's housing,
- have oriented the speed/temp insert within its housing such that the transducer's orientation arrow is facing forward and parallel to the keel,
- have verified that no hull features or marine growth are interfering with the smooth flow of water the
- and the problem persists,
then the fault would appear to have been isolated to the ST50+ Tridata. Unfortunately, Raymarine can no longer service ST50/ST50+/ST60/ST60+ instruments, necessitating that the ST50+ Tridata instrument be replaced.

Please note that the i50/i60 instruments are designed to essentially be drop-in replacements for ST60/ST60+. The communications interfaces of the i50/i60 instruments will support either SeaTalk or SeaTalkng communications protocols. A SeaTalkng Spur to SeaTalk Flat 3-Pin Adapter Cable is supplied with the i50/i60 instruments to facilitate daisy chaining the i50/i60 instruments to ST60/ST60+ instruments, ST600x/ST700x/ST800x autopilot control head (where x= 0, 1, or 2), D244 SeaTalk Junction Blocks, etc.