tacking angle

[fullandby]

Thanks for the feedback guys.
I have recently acquired a new headsail which has improved my tacking angle to about 100 deg. I sail in choppy water ( Moreton Bay) which probably doesnt help. Now I know that 90 degrees is attainable, I will work on forestay sag and sheeting angle.

Cheers,

Bart

[Dolphin]

Philip, This is how the plot was taken.
Firstly select a suitable sampling rate. If you select too high a sampling rate you end up with too many points and a mess. Go for a sail and collect the data you need.

I used the Garmin download software, “Mapsource”. It takes a .gpx file and plots it on a VERY rudimentary map. It also converts the .gpx file to a list of leg lengths and times, speeds altitudes etc. The speeds are integers of knots and some values contain extra strings eg. speed in whole knots and has <Space>kt in the field, ie 5 kt. I imagine most proprietary download software does this.
Here is a sample of the screen.

Garmin Mapsource Harbingers race a.jpg (58.37 KiB) Viewed 1880 times

Mapsource has a function where you can view the track in Google Earth. That is the one in the previous post that contains the track overlaid on the satellite picture. Good for reviewing tactics later.

To extract the data, open the file in mapsource and highlight one line, this is shown as a blue line of highlighted text. Use ctrl A to highlight the whole data file, then use ctrl C to copy the file to the clipboard.

Paste the file into Word and it comes up as a tab separated file. Because Excel will only operate on numbers and wont recognise numbers and text as numbers we need to strip the “<sp>kt” and “(Deg) True" and ”<Sp>m from the fields we need. Use “Edit” “replace” and replace the text with blank.

Select All (Ctrl A ) copy (Ctrl C) and open Excel. Then in the 2nd cell 2A paste the contents. (Ctrl V). your data is now in Excel and in a format that is useable,

[Dolphin]

Philip, Part 2
Because the file speed is in integers of knots we need to get the speed in real numbers. Take the distance and time to calculate speed. This is why we had to remove the extra text from the values. There are some differences from the calculated values and the GPS values. The GPS gives a summary page. I compare a simple speed and bearing plot to obtain the maximum speed.

20101229 Harbinger Speed and Bearing Plot a.jpg (43.66 KiB) Viewed 1880 times

I then compare the GPS's max speed with the max calculated speed from the graph and get a calibration factor. I apply that to all speeds.
I now have speed and bearing. Take the sine and cos of the bearing and multiply it by the speed. Excel works in radians so you have to convert degrees to radians, (deg/180)*PI. Take this and plot it in Excel using the X-Y plot function. You need to take away the bearing of the wind and there it is, you have a polar plot for the data!

Does it make sense?

Greg.

[Phillip]

Sort of Greg,

I only got a bit lost at the end, but will work it out when I try it over the next week.

Many Thanks,

Phillip
SEAKA