The basic choice is between an analogue paddle wheel which provides a signal directly from the hall sensor in the device and the Airmar DST800 Smart Sensor that provides speed updates via NMEA0183 or NMEA2000. There is no perfect answer as each option involves a compromise.
The best performance is achieved using an analogue paddle wheel. The d10 calculates the speed from an analogue paddle wheel 10 times a second giving a smoother and more immediate response to changes in speed. The Airmar DST800 Smart Sensor provides a speed update once a second.
*** note: All the major manufacturers use and rebrand Airmars transducers
so we've stuck to Airmar's product names below ***
Analogue paddle wheels
The most commonly available option for an analogue paddle is the Airmar ST300/ST800. We've done a lot of d10 testing using an ST300 and it's a great combination. The ST800 (Raymarine) and ST850 (Furuno/Garmin) are essentially the same device with different length bodies.
The Signet "Blue Cap" paddle wheel can be difficult to source but it offers better performance. The key difference between signet and other transducers is that the Signet emits more pulses per revolution meaning the d10 can calculate speed with less lag. Combine a d10 and Signet and the lag on the speed reading is just half a second, compared to 1.1 seconds for the ST300.
- The hole required for a Signet paddle wheel is significantly smaller than the hole for an Airmar transducer.
- There are NMEA0183 and NMEA2000 versions of the ST800/ST850.
If you are going to connect an ST800/850 directly to the d10 then pruchase the NMEA0183 version.
- The ST300, ST800, ST850 and Signet are all speed only sensors. If you want depth as well then a second hole will be required in the hull or you'll need an In-Hull CHIRP based depth transducer.
DST800 Smart Sensor/Triducer Multi Sensor
The current Airmar DST800 sends depth, speed and water temperature over NMEA0183 or NMEA2000. The big advantage is that you don't need a separate hole for a depth sensor. The disadvantage is that the DST800 only provides one update a second.
Airmar used to manufacture a Triducer with analogue paddle wheel and NMEA0183 for depth. If you can find one of these then it means 1 hole for depth and speed while still having an analogue speed signal.