Originally Posted by Whispering Wind
One of the approaches I am considering is using GPS SOG data as you do. Has not knowing indicated boat speed or current conditions impacted you any in what you do?
WW, the sailing I do is on a large open "lake" (for want of a better description) with well-known (and relatively small) tidal runs. I guess I've not used boat-speed for so long now (a couple of years perhaps?) that I've got used to not having it. It would certainly be useful in some of our races, but then I'd be tracking the lifts/knocks by watching the speed indicator all the time, when I can get the same info quicker by watching the sails and the way the boat is tracking through the water. If, from the GPS track, I think there's a current pushing me sideways, a quick tack confirms it and tells me roughly how much...
So to answer your question, IMHO indicated boat-speed is a "nice to have", especially if you have wind-speed instrumentation (on my boat I don't) - but GPS SOG is good enough for me. At the end of the day, whether they be anchorages or racing marks, I'm still sailing from Point A to Point B and those are fixed points on the surface of the earth, not arbitrary points on the water.