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Old 09-26-2007
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Garmin Display VMG's?

We have a Garmin 545s and we got it right when it came out software was 2.0 We went out racing a few weeks ago and noticed on another boats GPS it displayed VMG's Velocity Made Good to the Mark. I can't find it on our GPS, so I call Garmin they say i need a update so i get the update of there website, now my software is up to date at 2.6 now, and still can't find VMG's and now garmin is no help after several calls, I would think if we pick Navigate>go to mark it would show it, but it does not, any ideas?

Scott
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Old 09-26-2007
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Scott-

IIRC, you need to set up the data fields to show the VMG, rather than other less important data. When you're on the GPS screen, hit the menu button and select "Edit Data Fields" or something like that... and you should then be able to select VMG as one of the fields displayed on the main screen. BTW, VMG does not give you any information unless you have a route selected with waypoints.
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I've got a GPS 478 that has VMG and have a 450 that I just bought and also was looking for VMG but have not quite sorted it out either had not heard about a software upgrade for these yet
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Stony there is a upgrade for yours... https://buy.garmin.com/shop/store/do...D=148&pID=8056 All you need is a SD card, walmart sells a SD card and USB reader for around $15.

Scott
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Quote:
Originally Posted by sailingdog View Post
Scott-

IIRC, you need to set up the data fields to show the VMG, rather than other less important data. When you're on the GPS screen, hit the menu button and select "Edit Data Fields" or something like that...
If I recall correctly: On my GPSMap 498C, I have to press and hold the "cfg" key while in map mode, and that takes me to the data fields configuration screen. (Momentarily pressing "cfg" turns the data fields on/off.)

Jim
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Old 07-26-2009
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The Garmin current 400, 500, 4000, and 5000 series machines will not display VMG unless you have a wind instrument. This is a software oversight, and I understand a correction is is in the works. If you are navigating to a point, the VMG will read blanks, unless a wind instrument is present. tnx Bill
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Old 07-27-2009
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The concept of VMG is two different things. To a race instrument system, VMG means velocity directly up or down wind. To a GPS, it usually means velocity toward the next waypoint, also called WCV (waypoint closing velocity) or SOA (speed of advance).

To truly calculate VMG for a racing sailboat, you need a wind transducer so that the true wind direction can be calculated. Someone said in another thread that they have a GPS that can approximate the direction of the true wind, but I can't see how that can work well. VMG is calculated by multiplying the speed of the boat times the cosine of the angle of the true wind relative to our bow.

So is your desire to use this as a navigation aid or as a racing aid?
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VMG to a mark, on a sailboat, using just standard GPS VMG, is worthless unless you can head straight for the mark, which is usually only possible if you're on a beam reach. Then you don't need VMG because, well, because you're headed straight for the mark, anyway . (Exception: If current is a factor.)

There is a way to use VMG on such GPS', involving setting a phantom waypoint a couple thousand miles away, on the same bearing as the waypoint. But if you want to use your GPS for actually locating the mark, you'll need two GPS'.

Jim
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Most better GPS units have two forms of VMG calculation available, IE Ray, Garmin, et al. With a wind instrument, VMG is calculated as JArcher describes above. With out the wind instrument, the VMG calculation is done using the anglular difference between the course (rhumb) line, and the COG. This data is then also used to calculate the TTG, ETA et al. The non wind instrument calculation is not effective for tacking decisions, but the data is not with out merit if you understand what it is telling you. This second form of VMG calculation is what Garmin accidently overlooked displaying and is correcting. Tnx Bill
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Well the reason I asked the OP why he wantes to see VMG is because he mentioned racing. I'm solidly in the camp that having VMG reported is not very helpful while racing. I would prefer to see the true wind angle and velocity. Now I know if I have a shift in true wind direction or a shift in true wind velocity, which is much more useful.
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