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Using a Handheld GPS on the International Moth

Initially I was unaware of the avantages of using a GPS on my Moth for training or racing, until I spoke with ex-Moth World Champion Emmett Lazich. He said that he had been using one on the 49er in training and found them quite useful, if not a great toy at the worst.

I thought a GPS would also be very useful when using hydrofoils on my Moth considering how critical it is to be going as fast as possible all the time. I also do a bit of 4WD'ing as well, so I thought I might as well go get one, but I had no idea which one to get?

I found out that there are many different types of hand held GPS units out there at the moment, but it seems as though the main two brands are either Garmin or Magellan. Within each of these brands there are different types of styles to suit particular needs. Within each style, there are usually 3-4 different types of models.

Click to enlargeI decided to go with a Magellan Sportrak Map as it has the capability to load in highly detailed maps, including 4wd tracks and trails all around the world, is quite durable, reliable and has an excellent display for sailing. Whereas the equivilent in the Garmin is the eTrex Legend. They are both around the AUD$600 mark and both offer the ability to upload maps and download tracks onto your computer. Both units are also fully waterproof and take two AA baterries.

If you really did your homework, you could probably buy one overseas for a lot less, however be aware that these will not come with the basic Australian Maps pre-programmed into the GPS. Units like the Sportrak Map or eTrex Legend also come with extra memory allowing you to upload higher detail maps of particular areas. This map software is available at a cost of around $400.

Click to enlargeI also brought a bike mount kit with mine from Timeplus Communications in Brunswick, Victoria, as this would enable me to put the bracket on the front wing bar of my boat so I can easily view it whilst sailing. The GPS clips into the top of the mount, however I am paranoid about loosing this on the water, so I always secure it with duct tape as well.

There are numerous screens that you can have your GPS set to display. I choose to use the screen with the four large displays showing VMG, Speed, Maximum Speed and Heading. The numbers are not as big as a small digital compass, but you can read it.

In summary, here are some of the features that dinghy sailors might be able to find useful:

  • VMG - Velocity Made Good (determines how fast you are going to a particular mark on the course, usually the leeward mark, which is particularly useful when sailing windward/leeward courses)
  • Heading - the angle you are currently on
  • Bearing - direction to the next mark
  • Current Speed
  • Average Speed
  • Maximum Speed

So before the start, I would find the leeward mark, sail up hard against it and mark the waypoint into the GPS. Now whenever I am sailing downwind on a square run to that mark, I know my VMG.

On top of all this, I am always looking at my speed to try and make the boat go as fast as possible, even if I can get 0.5 knot out of a small sail adjustment. This is a little hard to do in a Moth, but a bigger and less responsive dinghy would make this a great feature to have. Then when I get on the reach, I am always pushing my boat to go as fast as possible and break my maximum speed record of 16.5 knots. I know I have gone faster than this, but unfortunately I didn't have it onboard that day.

Click to enlargeAn example of the Magellan PC software called MapSend can be seen here (click on image to enlarge in new window)...

This is an example of a race I did at Sandringham Yacht Club in Victoria with the wind coming from the south (bottom of screen). It clearly shows all the triangular course that I sailed on the first lap and the windward/leeward on the second lap, with the start/finish line located 1/4 of the way up the windward leg.

There are 36 different points located on this track, and each point has anywhere between 10 and 250 seconds of data in each point. This means that the GPS updates and records every movement, every second, to within 3-8 metres of your exact location.

At each second it records the following:

  • Exact speed (accurate to 0.1 knots on the water, but the software only displays it to the nearest knot)
  • Heading
  • Time
  • Trip distance
  • Elevation

The software also allows you to press the play button and replay the whole race in any speed that you like, updating the information mentioned above, from x1 speed (every second it will update) or x50 speed.

This is particularly useful to analysis tactics, speed and wind shifts. You can also load tracks over the top of your track to replay the race show two peoples movements if you like, pending that the person has the same brand of GPS as yours.

Feel free to email me though if anyone has any questions.

October 2004 - A friend picked up an awesome new wristwatch GPS recently and have only just found it on the Garmin web site. Only problem is the batteries don't last that long, but it is a neat little package. I think you might be able to get longer life batteries for this unit now tho. more...

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