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  #1  
Old 1 Week Ago
GeoffJ's Avatar
GeoffJ GeoffJ is offline
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Default Instrument expertise

I was reading Kevin Halls blog this AM (it over on SA), and I was wondering a few things:
1. Does VMG calculate a measurement of leeway, or does it assume the boat is travelling in a straight line? I do not see how it can measure leeway, so does it compensate somehow?
2. When you display "% of target", I assume this is target VMG not speed?
3. Is there a mechanism to adjust polars due to sea state (or other condition) on the box?
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  #2  
Old 1 Week Ago
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Schnick Schnick is offline
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On better processors like the old Ockam systems, B&G, and (I assume) top end NKE, there is usually a way to enter a leeway assumption into a table that correlates with windspeed. The way I saw Bob Congdon (pro B&G dude) calibrate this was to make a guess based on gut feel, and then spend about 12 hours tweaking the leeway up and down a few hundredths while comparing the wind data, heel number, and vmg and trying to get them all to behave properly against each other.

There are also super-sensitive multi-axis inertial motion detectors which are used to filter out lateral accelerations and can in some cases be used to compensate masthead movement due to pitching in waves. I first read about these during the Valencia era of AC boats? Surely they were around before then.

I haven't yet been on a boat displaying "% of target". When the target data is up on the instruments it's usually always a speed number.
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  #3  
Old 1 Week Ago
crashdog crashdog is offline
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Well, NKE will provide % target. Once you get to this level, you would be running Expedition or Adrena anyway, which does this kind of calculation more efficiently, and then you can push those numbers to whatever display you want.

One of the more useful targets is roll angle, since it is a good analogue for the so called wind weight or wind expansion factor. As to leeway, this is also a dynamical measurement that depends on trim v steering. You can work out a virtual model on leeway, but the second the leech tension on the main is adjusted, it all will need to be redone.

You realize that the article wasn't talking about instrument numbers, yes?
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  #4  
Old 1 Week Ago
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GeoffJ GeoffJ is offline
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Crash dog- yes I was aware but thanks for the clarification. I guess there is a lot for me to learn before I start messing with anything more than basic boatspeed, Windspeed and magnetic course.
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