I’m a sailor. I’m thinking of buying a cheap Android tablet with GPS to use as a chart plotter. Charts are free (in the US anyway). Of course there are dedicated marine chart plotters available, but as every sailor knows, once something is labelled “marine” its cost quadruples. Opinion? Suggestions? Dave Null
The best advice on this topic would come from people who have bought a smartphone or tablet, gone somewhere remote, switched it on and timed how long it takes the unassisted GPS system to find its location. It could take from 15-20 minutes to forever. I’d only consider a product that could do it in a couple of minutes. If your life was at stake, you might want it to work much faster.
Perhaps some Ask Jack readers have done this experiment and can recommend tablets that work well. However, you should try asking other sailors in person or in sailing-oriented forums, or ask for advice in the GPS Review Forums.
Unfortunately, it’s usually impossible to tell from the product specs whether a smartphone or tablet GPS works offline, and if so, whether it’s any good. But even if it has “real” GPS – usually a combo chip, not a dedicated GPS chip — it’s not going to be as good as devices sold by companies such as Garmin, TomTom and so on. Real GPS chips cost money and consume too much power. What you get in a smartphone or tablet is a very low power GPS that needs a lot of help from the mobile phone network.
How we got here
When smartphones started to become widely used, the US government was concerned that there was no way of locating users who called the emergency services (911 in the US, 999 in the UK). This led to the development of “GPS” systems that didn’t use the US government’s satellite-based Global Positioning System (GPS). Instead, they used triangulation (actually, multilateration) between nearby cell-phone towers or base stations. This muddied the distinction between any old location system and the real satellite-based GPS.
Today, the location system in smartphones and tablets works pretty well using triangulation from cellphone towers, input from in-range Wi-Fi, and tracking from your last known position. Indeed, it works without a proper aerial and no view of the sky. Add a bit of real GPS and the results are even better. This system is usually called Assisted GPS (A-GPS, AGPS or sometimes aGPS).
Assisted GPS greatly reduces the critical time-to-first-fix, because the device doesn’t have to scour the sky to figure out where it is. It already knows that, especially if it has been supplied with orbital satellite data over the mobile phone network. (This does not require Simultaneous GPS or S-GPS, which just means the device can receive GPS and voice data at the same time.)
In passing, further improvements in GPS come from America’s WAAS (Wide Area Augmentation System), which provides a network of ground-based reference stations. Similar systems are being implemented elsewhere, such as EGNOS, the European Geostationary Navigation Overlay Service, and India’s Gagan (GPS Aided Geo Augmented Navigation). However, I don’t know of any tablets that can use them.
So, the GPS systems in current smartphones and tablets work well because they already know where you are, because they remember your last fix, because they have tracked you on a cached map, and because they can get satellite information from the mobile phone network instead of from the sky. Try one in a shop and it should work well. Take it to a remote area, out of range of phone and Wi-Fi networks, and do a cold start, and it may not work at all.
There are plenty of places where you can sail while still within mobile phone range, and if you have maps and charts stored on the device, a tablet may still work well enough. (Trying to use server-based maps such as Google Maps would be a really bad idea, but you can preload small areas.)
If you still want a tablet, your best bet might be a Sony Xperia Z, Z2 or Z3 — all of which offer GPS, A-GPS and Glonass — or one of the Samsung Galaxy Tabs that also supports Glonass, such as the Tab 4 7.0. Glonass is Russia’s Global Navigation Satellite System, which is equivalent to America’s GPS. My guess is that manufacturers who support Glonass take satellite positioning more seriously than the ones who don’t. (In the longer term, we’ll also be looking for support for the EU’s Galileo and China’s Beidou Navigation Satellite System, which are undergoing development and testing.)
Samsung Tabs are the most popular Android tablets, which would give you the best chance of finding people who have used them “in the wild”, if not for sailing then for hiking or off-road biking etc.
If you’re sailing in places where your life might depend on GPS navigation working quickly and reliably, then it would be better to buy a marine system like the Garmin GPSMap 721, even though it’s more than twice the price. The 721 also supports “special sailing features” such as “laylines, enhanced wind rose, heading and course-over-ground lines, true wind data fields and tide/current/time slider”.
There’s another option, which is to use a cheap but powerful GPS receiver that connects to a smartphone or tablet via Bluetooth or a USB cable. The $99 Garmin GLO, for example, is “targeted … [at] users of tablets (such as the Wi-Fi iPad) that don’t have internal GPS chips and smartphones with internal chips that aren’t especially accurate,” to quote Boyd Ostroff.
You could mount your dedicated GPS unit where it has access to a clear sky while keeping your smartphone or tablet sheltered from the elements. This would also allow you to turn off the GPS system in your smartphone or tablet and get better battery life. Finally, you’d get a much wider choice of tablet, laptop or hybrid, including ones that run Apple’s iOS or Microsoft’s Windows as well as Android.