Garmin 405cx aboard an IOM


The 405cx gps-watch is small and light enough to just tape to the aft-deck of an IOM. Today's event in Tampere had 12 races but I missed a few due to electrical problems. Races 1 and 2 above, and races 7-12 below. It's funny how google-maps and google-earth show permanent winter and ice in Tampere 🙂


The raw-data ( is available in TCX format as well as Google-earth KML format from the garmin connect website.

Anyone have any software or matlab code to extract the instantaneous speed from this data and plot it? Might be useful for further CFD investigations or VPP-programs. Mostly light and shifting no1 rig the whole day. It will be interesting to compare with no2 and no3 rig in a real breeze.

Are there even smaller and lighter GPS-dataloggers? How long before we can have a GPS on every boat and watch playback of the race afterwards at home?

5 thoughts on “Garmin 405cx aboard an IOM”

  1. I have attended a couple of life size sailboat regattas where a number of boats (Corsair Tris) had onboard GPS units Afterwards, all were downloaded into the software after the race. At the bar that night, we watched realtime and up to 20x speeded up races. Very cool, as they had graphs for each boat including course, speed and VMG displayed along with the boats on the race course. With small, thumb drive sized, GPS data loggers we could do the same at an IOM regatta.

  2. Hi Anders,

    I have a small GPS logger. It is availabe under IgotU or GT-100 GPS logger. It is small enough to fit in the Sailsetc. screw top radio pot with a standard 6xAAA batterie and reciever.
    I did some logging in my Marblehead in 2008 and got some impressive speed calculations in third suit rig conditions :o).

    Cheers Nigel

  3. Hi Anders
    I have used the eagle tree system, with the gps and water , windspeed, servo current and battery voltage.
    Water speed was installed in the keel just under the boat hull, but was not a good idea. The wind speed was never calibrated, but did give a good indication of the increased wind speed due to aparent wind over the ambient wind speed. I never got to making a wind direction indicator, and have been looking for a "hot wire" wind speed indicator as I was not happy with the rotory one I built. The system ddoes have potential, and all the speed graphs can be displayed on the laptop either live or for analasis afterwards like you are wanting to do. I see the new gps has better resolution as well. in sailing that was a bit of a downfall of the unit I have. This exersise has us looking to make a wind tunnel for testing in. May take a while though.

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