The Raymarine ST 60 Wind instruments can calculate the TrueWind Speed (TWS) and True Wind Angle (TWA) from the apparent wind data (AWS& AWA) and the boat’s speed.
Unfortunately, they’ll only do this from the speed as measured by apaddlewheel in the water. This measures theboat's speed through the water and is itself an apparent measurement, as opposed tothe true Speed Over Ground (SOG) that can be obtained from a GPS receiver.
There is some disagreement among sailors as to whether thetrue or apparent speed should be used for the true wind calculation.
Frankly, I think those using an apparent speed definition are from oldersources that haven’t fully incorporated the changes that GPS has made tonavigation. For my boat, I want to usethe SOG in the TWS calculation. I alsowant to see the SOG displayed on my other Raymarine instruments that are designedfor the paddlewheel.
Opinions true vs. apparent aside, Take Two’s paddlewheel is not accurate and I’vebeen unable to calibrate it. I think theproblem may be because of water turbulence where it is mounted. Keeping the paddlewheel in the water all thetime gets it fouled with growth and swapping it in and out with a plug getswater in an otherwise dry bilge.
The solution that works for me is a SeaTalk NMEA Bridgefrom gadgetPool.de. Its primary purposeis to translate sentences between a standard NMEA instrument network, and Raymarine’sproprietary SeaTalk network. I don’treally need it for this purpose, but it has a very nice feature to specificallyaddress the speed problem. When the optionis enabled, the bridge can translate the SOG sentence from the NMEA network intothe SeaTalk sentence from the paddlewheel.
This effectively tricks the Raymarine instruments into using the GPSspeed.
I’ve been using it for about a year now and it works well.