Have a new Garmin GPS. Found out it has a VMG display. Set it up and used it during our last race. Didn't really use it - just looked at a few times to see what it was showing. There must be a magic part of a point or a reach where the VMG will tell you what to do. Any comments regarding VMG (velocity made good) in a racing situation would be appreciated. RD
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VMG
..is the key to success in racing. Forget ALL the other instruments and their readout. When you optimize VMG you are sailing the best course/speed combination that you have available. Be aware there are various VMG's. There is a VMG to a mark, and another to windward and they are not the same. You always want to sail the windward VMG on a beat. Likewise you use it on a run to the leeward mark. This will tell you the best reaching off course to hold before you jibe.
..is the key to success in racing. Forget ALL the other instruments and their readout. When you optimize VMG you are sailing the best course/speed combination that you have available. Be aware there are various VMG's. There is a VMG to a mark, and another to windward and they are not the same. You always want to sail the windward VMG on a beat. Likewise you use it on a run to the leeward mark. This will tell you the best reaching off course to hold before you jibe.
V,M.G. info needed
Can anyone explain in some detail how to use VMG when racing- what do you look for to help with a tack?
Can anyone explain in some detail how to use VMG when racing- what do you look for to help with a tack?
VMG
All other things being equal (which of course they're not), when sailing upwind to a mark, you want to maximize your VMG. Every boat (at a certain wind range, with certain sails, etc) will have a beating angle that provides maximum VMG. If you sail that angle, you will get to the mark the fastest your boat can for whatever course you choose. BUT!!!! nothing is equal. your optimal VMG angle will vary with wind speed, chop, angle of heel, sails, and sail and rig tuning. If you adjust your sails (sheet tension, sheeting angle, etc), you could cause your optimal VMG angle to change. Also, you could be maintaining your maximum VMG, but it wont help if you don't watch where you are going, stay in the strongest wind, tack on the good shifts, etc. Many people will generate polar plots of their boats performance. Serious racing programs will collect enough data to have a polar plots for wind strength and sail selection, wind strength and boat speed. At that level, the data will tell you when to change up or down to a different sail, and what your target boat speed is for the wind strength and current sail selection. Take a look at the link for some examples this approach. Chris
All other things being equal (which of course they're not), when sailing upwind to a mark, you want to maximize your VMG. Every boat (at a certain wind range, with certain sails, etc) will have a beating angle that provides maximum VMG. If you sail that angle, you will get to the mark the fastest your boat can for whatever course you choose. BUT!!!! nothing is equal. your optimal VMG angle will vary with wind speed, chop, angle of heel, sails, and sail and rig tuning. If you adjust your sails (sheet tension, sheeting angle, etc), you could cause your optimal VMG angle to change. Also, you could be maintaining your maximum VMG, but it wont help if you don't watch where you are going, stay in the strongest wind, tack on the good shifts, etc. Many people will generate polar plots of their boats performance. Serious racing programs will collect enough data to have a polar plots for wind strength and sail selection, wind strength and boat speed. At that level, the data will tell you when to change up or down to a different sail, and what your target boat speed is for the wind strength and current sail selection. Take a look at the link for some examples this approach. Chris
Where to get polars ?
There used to be a website that would allow you to upload you GPS tracks and it would produce some polars. But because it did not have complete data (current, accurate wind, etc), it might not have been that accurate, but maybe good enough. I believe that some software packages (Ockam, and others) will provide this for you if you connect your instruments to your computer. Raymarine has a NEMA/Seatalk bridge device that will convert all seatalk messages to NEMA which can then be logged to your computer. If you have GPS, Wind and Speed instruments, then you should have all the data you would need to create accurate polars. I'm sure some software can be directly connected into such a system to generate plots. I believe that RayTech RNS software will do this for you. Chris
There used to be a website that would allow you to upload you GPS tracks and it would produce some polars. But because it did not have complete data (current, accurate wind, etc), it might not have been that accurate, but maybe good enough. I believe that some software packages (Ockam, and others) will provide this for you if you connect your instruments to your computer. Raymarine has a NEMA/Seatalk bridge device that will convert all seatalk messages to NEMA which can then be logged to your computer. If you have GPS, Wind and Speed instruments, then you should have all the data you would need to create accurate polars. I'm sure some software can be directly connected into such a system to generate plots. I believe that RayTech RNS software will do this for you. Chris
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