I love the easy ones.
Raymarine only uses STW (from the paddlewheel) to calculate true wind. With the paddlewheel in the bilge the algorithm gets 0 so true = apparent. Clean your paddlewheel and stick it in the hole.
That's what I suspected. First thing I looked for was a menu in Dealer Setup that would allow selecting SOG for this, but didn't find it in the manual. As I'm sure you know, SOG is a much more reliable and accurate basis than SOW for the required vector calculations. I guess the only logical explanation for doing it that way is that GPS speed was much less common back when the ST60 series was developed.
Unfortunately my paddlewheel is in a very inconvenient location. The air conditioner tray was installed right over top the through hull, which makes it all but impossible to reach. If I could contort my arm and wrist to get to it, I am really concerned that I might get the blank plug out, and not be able to get the angle right to get the paddlewheel (or the blank) back in. Meanwhile, the water continues to pour into the bilge.
Also, my paddlewheel is not free-wheeling. It has severe resistance, so it needs servicing. I can't figure out a way to disconnect the cable to get it to a work bench where I might be able to do some decent cleaning on it. (Any hints on how to do this?)
It is good to have an explanation for this, so I can stop wondering what's wrong. (Thanks!) I will just use apparent wind for now.
I have a few options to circumvent this problem. I have a Raymarine-NMEA converter from my old boat that could take the apparent wind from SeaTalk and feed it by Wifi to my tablet software that can convert to true wind using SOG from the GPS. I doubt that the converter will fit into my NavPod, so running the wires to a remote location will be a tedious job. That will go on my ever-growing list of winter projects. Maybe someday I will get to it.