GPS Unit details

[sukhdev]

I got a few messages asking for details of the GPS I use, here is the info:

The model is the Garmin Etrex. There are a couple of Etrex models, but for speed measuring the basic model is fine. This is a 12channel GPS (uses up to 12 satellites). It can fix your position up to 15metres accuracy and for speed it is accurate up to 0.05 meters per second (it can easily measure your walking speed & is far more accurate than car speedometers).

The unit is very easy to use, we don't really need the navigation stuff, as for speed, you get max, elapsed time, average and current speed.

Although Garmin claims its submersible, don't try it, I ended up destroying my first one. Use a waterproof mobile phone bag (available at Marinetech).

details of the product are at http://www.garmin.com/products/etrex/

you can buy it in Singapore from O'Connors at:
98 Pasir Panjang Road, contact is Winston Wong at 6470 4757 or email him at wong.winston@oconnor.com.sg.

Its available far cheaper online if you look around. Singapore price is SGD255.

Another excellent unit is the Magellan, but its much more expensive. Most of the watch based GPS are useless, though I am waiting for a Suunto M9 which promises to be a breakthrough but at a steep price (US675). I should be reviewing that unit in a few weeks time.

[MennoB]

Hi Sukhdev (and others),

You might want to check rec.windsurfing (or may already have done so), because there has been a lot of discussion over there about use GPS for windsurfing.
Not only which brand and type is best suited, but also on how well (or not) they can handle submersion.

Here's a link to rec.windsurfing, with GPS already entered as search criterium.

http://groups.google.com/groups?hl=en&lr=&ie=ISO-8859-1&q=GPS&meta=group%3Drec.windsurfing

[ozymandius]

Sukhdev,

I had been reading postings on the use of GPS systems for speed measurements on the rec.windsurfing newsgroup quite a long time ago. It was pointed out at that time that the max speed reading could be quite erroneous because the instrument would pick up very short bursts of speed caused by your body jurking forward when you hit a chop or something like that. I don't know if you can overcome this sort of thing.  Maybe your instrument has got a feature for measuring the max speed which is integrated over a short period of about 1 or 2 secs which will smooth out such bursts of speed?

You might like to know that the Europeans are working on putting up their own GPS systems based on 30 satellites to rival the Americans.  They call it Gallileo.  Should be up in about a year's time.

[sukhdev]

Yes, thats a well known phenomenon. The average speed reading pretty much takes care of that. I've downloaded tracks and its easy to see the occasional spurious reading. This tends to be not far off the rest because its an extrapolation of previous readings (I am guessing a bracketing algorithm is used).

Once the unit has a solid lock the spurious readings tend to fall off. My own experience in 15 knot type winds is that very few such readings happen.

The next unit I'm getting..the Suunto M9 seems to have a lot more features oriented specifically at tracking sailing. It has an incredible start line feature; you set the start point and countdown time, mark the line, the unit then continously tells you how long you will take at your current speed & position to sail back to the start line.