Latest News: Forums Technical GPS tracks and upwind beating

  • This topic is empty.
Viewing 5 posts - 1 through 5 (of 5 total)
  • AUTHOR
    POSTS
  • #4079
    matoi
    Member

    Hello!

    I have taken a look at some tracks that my small Garmin eTrex GPS recorded this summer.

    An odd observation:
    It seems that when you “save” the track via commands on this device, for purpose of giving it a meaningful name, clearing memory for next sail etc. – the device discards the time and speed data. It’s silly but a quick google search revealed that the whole family of these gadgets does the same thing. So, if anyone is using a similar device and wasn’t aware of this before, take care. It seems that the best practice is to just switch the thing on when you want it, and switch off when you’re finished sailing for the day, without any further fiddling with menus and commands before downloading data onto computer. The device will keep all the data with it’s own naming system “Active log 001, Active log 002, 003…” and the information regarding speed, time, position, heading and so on will be kept complete.

    An (somewhat embarrassing) question:
    Looking at this data plotted on the chart, it seems that we had difficulties achieving better angle over ground than about 110-120 degrees between port and starboard leg (as far as I could detect we never encountered significant current). On the other hand, on the water I never had an impression that there was some big problem with pointing. Unfortunately there were very few other dinghies where we sailed to compare to, but our pointing seemed similar to keelboats. Looking at the compass it seemed as if we were able to achieve about 95-105 degrees pointing angle. Of course the boat needs some leeway, but I didn’t expect it to be so much. It’s confusing, so I would appreciate if anyone could share their opinion (especially if you analyzed your upwind tracks in a similar way). As I’m unable to race against similar boats, I would like to have some idea in a numerical form, which I could use as a reasonable benchmark for further practicing.

    Thanks and best wishes to all,
    Mato

    P.S. Perhaps I should have mentioned that we tried to follow the basic suggestions for good upwind sailing, like putting enough rig tension to avoid genoa luff sag, sheeting the main close to centerline, taking care that the centerboard is smooth and all the way down, though perhaps we were not meticulous enough at keeping the boat flat… šŸ˜

    later edit:
    taking a better look it seems that sometimes we had tacking angle (over ground) under 110 deg, but still far from 90…
    [attachment=0:1x8mlt6q]tacking test1.jpg[/attachment:1x8mlt6q]

    #9547
    bigal
    Member

    First thought relates to the position of the fairleads ; the cruisers I’ve seen have them too far out . The P&B tuning guide states the track should be 21″ from the centre line .

    #9548
    howard
    Member

    Are you quite sure you were in still water?

    The tacking angles are worst at the point you might expect more current – close to a headland. If the channel is actually narrower there (I can’t tell from the extract) then you can probably blame some of this on tide.

    #9552
    matoi
    Member

    Thanks for replies.
    Bigal, I think the fairleads are in a good position as they are in the middle of the side benches (it’s a World).
    Howard, I hope you’re right. Your post made me calculate a little, and it turns out (if I did it well) that even a current of 0.5 kt (which might have been unnoticable to me then and so regarded as insignificant) widens a theoretical tacking angle of 90 deg to 101 degrees. And it’s quite possible that it was a bit stronger around the headland.
    If anyone would find it amusing I’ve attached the illustration that I made.
    Thanks and best wishes,
    Mato

    [attachment=0:3emmkom9]WPA.jpg[/attachment:3emmkom9]

    #9555
    mhardman
    Member

    2kn current last week and light winds, our tacks were superimposed on the GPS. Then as the current dropped they began to separate.

Viewing 5 posts - 1 through 5 (of 5 total)
  • You must be logged in to reply to this topic.