Saturday, July 14, 2012

SAC: Paper charts vs Raymarine chartplotter vs iNavX on iPad / iPhone

Its a good idea not to rely on a single source of navigational information.

To sail to the Arctic Circle we had charts in paper form, plus chartplotter plus iNavX on iPad. On the last day before leaving in a moment of you-can't-be-too-careful I also bought the charts for iNavX on my iPhone as well.

So how did they compare?

Paper Charts

It's a good idea to have these just in case of a catastrophic failure of the electrical system and we did get them out from storage as we progressed along our route. However we didn't actually use them much, apart from when planning approaches to land, and then mostly by Tristan as I'd just pull out my always to hand iPhone.

A backup then, not the primary tool for navigation.

Raymarine Chartplotter

This was in practice the main navigation tool, located as it was on the chart table handy for the log book. It was also integrated into the other electronics, such as the VHF's DSC, the radar and the AIS (which stands for Automatic Identification System). The AIS meant that if the radar spotted something you usually could put the cursor over the target and get the ship name, heading etc and if necessary could call them over the VHF by name.

The data it used was Navionics, so actually the same charts as used by the iPhone and iPad.

Generally it worked well though there were some weird things. As previously blogged at times the change in latitude and COG were not consistent and that was worrying, particularly, such as when trying to make Reykjavik without tacking, it mattered.

The AIS sometimes seemed to think the empty seas not worth waking up for and fail to work, plus the radar could interfere with the GPS lock, but it did its job (unless you really, really needed a COG that you could trust).

iNavX on iPad

I was pretty pleased with this. It had the same Navionics chart as the chartplotter and could do similar calculations of COG, manage waypoints, routes etc. While it didn't connect to the radar and AIS it has the ability to do so (wirelessly I guess) plus it had the ability to download weather data in GRIB form.

It could also be used safely on deck due to the waterproof case which for pilotage, for example through the Faroe Islands (above), was pretty useful. It created the track which could then be exchanged via Transverse with the iPhone (and vice versa) or emailed in KML format.

This was all great but using the iPad with GPS on all through the Faroes drained the battery and then when plugged into the 12 volt socket it went all "I'm too magical for this dirty power supply" and refused to re-charge, which meant it was useless until Iceland.

Yes I did test it out on Goldeneye, but alas while attached to shore power.

Moral of story: test electronics when disconnected from shore power.

iNavX on iPhone

The iPhone was a bit more tolerant of the low amps and varying voltages of the yacht's power supply and charged just fine. The software was similar but not exactly identical to that on the iPad - sometimes in a better way (for example its easier to say "Goto waypoint" on the iPhone than iPad). Again the charts were from Navionics.

Of course the screen's a lot smaller but when the magical iPad gave up we had to rely on it for downloading and viewing GRIBS. So that last minute urge to have the iPhone as a backup to the iPad turned out to be a good one.

However the next / back on-screen buttons for the GRIBs were way too small.

There was one strange omission on iNavX on both iPad and iPhone which was the lack of tidal data (or at least I couldn't find it). But if you downloaded the Navionics application (chart) you could click on the map and see tidal flow and direction.


Paper charts seem expensive when you consider how they're not often used, but then they're like EPIRBs, you need then to be there just in case.

But Navionics did rather well out of us as we bought the same data four times (chartplotter, iNavX iPad, iNavX iPhone, Navionics app iPhone) which all added up.

There was no ideal do it all solution, and maybe its not right to rely on just the one. The iPad was pretty good, but would be better iNavX also had tidal flows and the magical device could be recharged.

The reality was that the Raymarine chartplotter was what we used the most, integrated as it was with the rest of the yacht's systems.

However think of this: as we approached Reykjavik the only device onboard that could reliably give us our COG and determine whether we should tack or not was a phone.


O Docker said...

Sometimes the best insurance with finicky chargers is to carry a low-power inverter and to plug the device charger you'd use ashore into that.

But even a discharged iPad can be used to measure COG. Just tie it to a float with a line long enough to reach the bottom and toss it overboard. Take a bearing on the float as it recedes astern, and the reciprocal will be COG.

JP said...

Two top tips there, O'Docker