How fast?

We take a look at some of the GPS brands on offer

Wednesday December 5th 2007, Author: Toby Heppell, Location: United Kingdom
In recent years the use of GPS technology has become more commonplace among dinghy sailors. A significant reduction in size is primarily responsible for this, but people are becoming more and more interested in the speeds they achieve out on the water during both training sessions and regattas.

There are a number of things GPS units can be used for on dinghies, from simply logging speeds to improving performance on the race course. So when looking at a GPS unit consider what you are actually likely to be using your unit for. Perhaps the most important question is will you be able to use your GPS while racing? In most dinghy classes the answer will be a resounding ‘no’, with many classes having a rule specifically to inhibit electronic data devices and others having a catch-all whereby if something is not specifically mentioned in the rules then it is simply not allowed.

Exactly what you will use your unit for will of course affect the features you require. If, for example, you sail in a class that has voted to allow such devices when racing, you may well want a GPS that can work out VMG in addition to just speed and with a large screen, allowing you to see the numbers from a distance away. However, if you are looking for something that is simply there for your own interest you may want nothing more than a waterproof device with a log feature, able to show you your top speed at the end of the day. Of course if you are planning on doing some serious boat speed training, again the large screen and VMG functions will be important, as will an ability to download tracks (ie where you have sailed) and analyse this data on a PC. It is worth noting that due to equipment constraints on small boats, devices able to give VMG feedback are only able to do so based on a user manually inputting wind direction.

Those using GPS units on the water for training find they are a useful tool. However they do have limitations. Most importantly GPS measures speed over the ground not through the water as the boat speed measured by an impeller on a yacht would. Therefore speeds will include the effect of tide. Also the real time speeds off the shelf GPS units give are not always exactly accurate. GPS units work on a complex timing system requiring data to be received from three or more satellites at any one time. This constellation is constantly moving around overhead, so as old satellites ‘disappear’ to the GPS unit on your boat it picks up new one and while this handover happens there can be a slight glitch in the speed readings, despite some units being capable of monitoring up to 12 satellites simultaneously. Ionospheric and Troposperic effects can also make a difference to the accuracy of any GPS device and a GPS antenna is also sensitive to where it is mounted requiring the maximum view of the sky (therefore strapping it on to the back of a carbon fibre mast is not the best place for it).

There are, in effect, two major players in the dinghy GPS world - Velocitek and Garmin. However, although there are (realistically) only two main manufactures out there they both have a variety of units to choose from, giving plenty of option when buying.

Velocotek SC1:

The Velocitek SC1 is a dedicated sailing GPS unit. Interestingly the SC1 only has compass and speedometer modes enabled straight out of the box and requires you to download a (free) programme to access some of the other functionality.

The SC1 has one set of particularly large digits on the front of the screen (30mm tall) and one set of slightly smaller numbers. Due to this, the device is only able to display two of its multiple functions at any one time, although it is highly visible. The range of functions the SC1 can display are as follows:

Maximum speed recall
Best 10 second average speed recall

Adjustable damping
Programmable artificial declination for direct comparison with a magnetic compass

Tactical Compass
Displays your heading relative to the wind direction
Makes wind shifts easy to identify
Display shows the same number at equivalent angles on either tack

Calculates and displays upwind and downwind VMG in real-time based on a user-programmed wind direction
Responding to wind shifts in Tactical Compass mode automatically adjusts the wind direction used to calculate VMG

1-9 minute countdown sequences available
Sync. button
Loud audible signal

Start Line Proximity
Indicates distance to start line in metres or boat lengths

Clearly with much debate surrounding the use of GPS units the SCI’s ability to tell you where the line is will have many unhappy. The reality, however, is that these types of products are continuing to become cheaper and more accessible so a debate needs to be had in most classes as to what can and cannot be used when racing.

RRP £225

Velocotek (S10): £150

The S10 is Velocitek’s slightly older and less feature-filled little brother. Technically the device has been replaced by the SC1, but some can still be found second-hand or in old dealer stock and it is still being widely used. Once again this unit features the big easy to read digits and like its big brother, the S10 is fully waterproof and able to float, a big advantage to the racing sailor.

Unlike the SC1 the S10 is only able to display one set of data at any one time, making the uses for this device during racing even more limited. The features the device is able to display are as follows:

Real Time VMG
Real Time Speed
Max Speed Recall
Best 10 Second Average Speed Recall
Over 10 hours of GPS Data Storage in Flash Memory
Fast Data Downloading Through a USB Link
Downloaded data is automatically formatted for use with Kattack, GPS Action Replay and Google Earth
Watertight to 25m (75ft)
Only brand of GPS unit able to float

With the Velocitek units data can be uploaded from several GPSes onto the same programme and replayed. This means that after racing you can take several feeds from top boats and use it to debrief sailors or as a training tool. Although we are sure this can be done with other models, the Velociteks are the only units we have actually seen this, or heard about this being done.

RRP £170

Garmin Foretrex (201):

If the two Velocitek options look like the wild, zany, rad young extreme GPS units then the Garmin Foretrex 201 could well be their father. It looks much more sensible and geeky, without the big colours and numbers featured on the SC1 and S10.

It is also clear that with the Foretrex 201 we are moving slightly away from the sailing specific GPS units and into a world of outdoor units. This specific model is designed to be worn on the wrist and, is bigger, but just a little heavier than most watches. There is some debate as to how much wearing a GPS unit on your wrist will effect the speed readings. Some say that if you are making big arm movements this is bound to have an effect on speed readings, while others state that GPS is simply not that sensitive (the latter is true). Of course the 201 does not have to be worn on the writs, it can be mounted somewhere on your boat, though the Garmin’s display is much smaller than either of the Velocitek units.
Features included in the 201 are as follows:

Easy-to-read hands-free GPS navigation
Lightweight, waterproof wrist-top GPS perfect for any activity
500 Waypoints and 20 reversible routes
10,000 Track log points
Configurable trip computer displays speed, distance, location and much more
Racing timers: configurable start sequence, alert tones and large-number digital readout
PC connectivity
15 Hours lithium-ion battery life
Size: 43.18H x 83.82W x 17.5D mm

RRP £179.99

Nauteek SC100:

Perhaps designed more with the small sportsboat in mind than the dinghy, the Nauteek was recommended to us a functional piece of kit. It has a large screen to display its various functions and is designed to be mounted on a boat. The Nauteek SC100 can display the following:

Speed Over Ground (SOG)
Course Over Ground (COG)
Countdown timer with one-touch synchronisation
Display changes automatically after countdown timer
Chronograph starts automatically after countdown timer
GPS position
Statistics (trip, max speed, average speed, elapsed time)
14 hours recording capacity at 1 second intervals (recording capacity can be increased by increasing the interval)
Waypoints (new waypoints, variation of course to next waypoint, detection of waypoint, goto next waypoint). This function will be available in 2008 for new devices and previously purchased devices via USB firmware upgrade

The Nauteek SC100 also has a bigger brother, the SC200, which is able to perform a number of additional tasks, including VMG, true upwind direction and distance to start-line as well as a host of others.

It is clear both of the devices have been designed by reducing the size, power needs and complexity of keelboat electronic tools. As such they seem to offer a great deal of useful, tools to the racing sailor.

RRP SC100 £299.00
RRP SC200 £399.00

Garmin eTrex:

Firmly in the world of non-sailing devices, the Garmin eTrex combines intuitive, easy-to-use features and a rugged exterior into a lightweight package that is only four inches high and two inches wide. Although clearly not designed for the racing sailor, it does offer a cheaper entry into GPS technology and is waterproof. The unit features:

Rugged, waterproof case in high visibility yellow
500 waypoints and 20 routes
1536 track log points
Multiple map zoom levels
Customise trip Computer
PC Connectivity

RRP £95.95

Who uses them:

Interestingly the first thing that is clear about GPS units is, although they are being talked about a lot, there are still not huge numbers of dinghy sailors using them. Currently most of the units are being used by those who sail fast boats, such as the Moth or the Musto Skiff.

Adam May – top Moth sailor and Paralympic coach:

I currently use the Garmin Foretrex 201. I've made a little centre mount for it on the Moth, and it works really well. It has big numbers for the display, but the functionality of a proper GPS if you need it (I've used mine as a useful coaching tool). My 2.4 squad use them as well in training. It is a useful safety feature for sailing in China that you can set a waypoint and know you can get home if the visibility is bad!

I'd like to try a Velocitek one though.It is a good sailing specific unit, and I think they've got the software doing some neat stuff now. But the 'Fisherprice' look to it doesn't appeal though.”

Rohan Veal – two time, and current, Moth World Champion:

“I use the Velocitek SC1, not only because I am sponsored by them, but even if I wasn't, I would still use it.

The main advantage of it over any other unit for me is that:
You can read the screen output from anywhere in the boat
You can choose which two displays you want to read on screen
It is 100% waterproof
It is shockproof
No need to open the case to turn the unit on or off
Excellent support and warranty
They float too!”

Rick Perkins, UK Musto Skiff National Champion:

“I use the Velocitek S10. We used them at the World Championships this year but I was using one before that. To me one of the best feature is the playback you are able to do.

For example we have a number of GPS traces in video format on the Musto Skiff website ( ) from several different races and training sessions. We have a guy with a Musto over in the USA and he was able to download a training session between Richard Stenhouse and myself, analyse it and see where he needed to improve. He could look at the screen and see he was coming out of the tacks slower than us and then know that is an area he needs to work on.

I do worry about the ability on the new models to put in a start line and see how far you are away from it. I think there needs to be some discussion about the future of GPS units. They are already available in everything from phones to watches and this is set only to increase. This means they will be on the water anyway, so we might as well discuss what the rules are now.”

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