Many thanks to Hartmut [hwecken] and Patrick [tiersp] for their help getting this to work. Hartmut helped with a large recorded file and advice, and Patrick with an updated Polauto version. What follows is an email
dialogue about some details to consider for recording polars with Hartmut's comments added -which he allowed to have posted.
The first thing I did this morning was download and run your nmea file with NavMonPC, OpenCpn and Polauto running in tandem each using a separate Virtual com port set up in NavMonPC, as you suggested. Watching Polauto work graphically with Opencpn actively charting is quite a treat, how exciting. I did not put any filters on (10-10-10-1s) and the Polauto drew some reasonably good polars with your file without my intervention. They were not nearly as complete as the one you posted, but with some additional work, I can see how more accuracy would be developed. Thank you for the file and your description of sail conditions and route
, that kind of notation appears to be essential for interpreting and obtaining good polar recordings.
I've been thinking about your response to my questions and observations about filtering:
"The more you filter all the values in polauto the more realistic the polar will be. In upwind conditions you must filter more because when you are coming to the edge you are overshooting in boat speed. I think for broad reach or run courses filtering is not so essential.
For me, it makes no sense to filter the raw data, because you will loose information and you will need a lot more data."
Without having any experience in this, I think I would agree with you about the need for filtering upwind more than downwind. Do I understand that correctly that normally you do not use filters upwind either?
I do not use filters in NavMonPC.
In Polauto you must use filters otherwise you will get too high values due to overshooting when changing course.
Polauto - under Conf - Data Filters -
Maximum Difference in Boat Speed 1, 3, 5 & 10 nds
Maximum Difference in Wind Speed 1, 2, 4, & 10 nds
Maximum Difference in Wind Direction 1, 2, 4 & 10 nds
Average on Time 1, 5, 10 & 15 seconds
Patrick's note: "No filter use 10-10-10-1s"
The more you filter the more data you need, the longer time you need to get an polar but this polar will be more accurate than with lower filters. I use filters in all directions (upwind and downwind).
NavMonPC - under Options Filters -
SOG Filter - 2, 5, 10, 15 & 30 seconds
COG Filter - 2, 5, 10, 15 & 30 seconds
HDG Filter - 2, 5, 10, 15 & 30 seconds
AWA Filter - 2, 5, 10, 15 & 30 seconds
TWA Filter - 2, 5, 10, 15 & 30 seconds
TWS Filter - 2, 5, 10, 15 & 30 seconds
TWD Filter - 2, 5, 10, 15 & 30 seconds
my configuration is no filter
These filters average the value over 2,5,10 or 30 seconds.
NavMonPC's Windchart and Speedchart graphics are pretty good.
It appears the wind direction oscillates much more than we may realize just looking at tell tails.
NavMon allows you to Play a nmea file, Options-Filter it and Log the output.
That Log file could then be sent to Polauto.
NavMon appears to be very feature rich.
Yes, but I use it only to bring the nmea streams to the virtual com ports, and somtimes to log windchart as an overview what had happen on a trip.
I suppose only experience will inform us what filtering is best, but Polauto seems to work pretty well. I had thought that to get good polar data one should record
sea state, sails
, sail trim, current
(preferably slack) and any small changes. Then I had thought it was best to get a segment of data with all these variables held constant for awhile and then pick that data from the recording.
I think it is good to have som variables like seastate or sail usage. Seastate is realized now in polauto 4.
I will separate in future only between offshore and inshore because seastate corresponds in my opinion very close to windforce, but ther is a relevant factor how shallow/deep is the water. In my case on Ijsselmmer you get up from 5Bft a short steep breaking wave, on the other hand with same conditions in the northsea the waves are longer, may be higher but you can sail faster.
Have you had Polauto running long enough so that you know whether judicious use of the Polauto Record
on/off button is effective?
Yes this is a good feature to exclude maneuvers like tacking or setting sail.
Also, perhaps you can advise regarding connecting my instruments. I have Raymarine Seatalk
instruments and a Garmin
, with a Globalstar
connected to VHF/DSC. The GPS is not a problem, but I need to convert seatalk
to Nmea0183 and I will want to get AIS sometime. Should I be considering a Multiplexer rather than a Raymarine
seatalk - Nmea converter? If so, which one?
Have a look at this link http://www.busse-yachtshop.de/pdf/seatalk-nmea-interface.pdf
Not realy cheap, but I think it fits your problem
Also do you mind if I post the above, with your comments, along with some shots of the 3 programs running your file?
It is ok for me
Thanks, so much.