But they have a gotcha that can get even the best navigators, as the Volvo Ocean Race's Team Vesta found out to their cost - see this post on SA via Noodle.
Take the patch of water above, which is just north of Iceland, viewed today using the Navionics Web App. Looks pretty clear doesn't it? Contours at 200 m and 500 m, just great, clear sailing. One island called Grimsey near the coast but when sailing there in 2012 we were far away.
Only it isn't clear at all. Take that harmless sounding reference to Kobeinsey (which I've added a red circle around). It looks like a description of that patch of water but look what you see if you zoom in:
This is from the Navionics charts on the iPhone for the same region, zoomed into so you can see that Kolbeinsey is actually a small island, or maybe a large rock.
Ok, it might be just 7.5 metres or so across but that would have been enough for us to prang Goldeneye something nasty when we sailed there in 2012. Confession time: it wasn't me that spotted this but Tristan: good thing one of us was awake.
But it shouldn't be like this: charting software should always show land, even when zoomed out.
Until then, let's be careful out there.
Updated: very interesting article about the wrecking of Team Vesta by Yachting World's Elaine Bunting here.