Laptop Navigation - with a Mac?

Earlier in the year, while the (now demised) yard was busy sort-of-but-not-quite finishing off the few loose ends on Arabella, I embarked on a new project: creating a laptop computer-based GPS/Chartplotter system with the capability to receive and overlay AIS data at a later date. There were one or two difficulties to overcome. I own a Mac laptop. And I needed to work to a budget - ideally about £250 or so.

I've mentioned before on this blog how much I'd love a fixed chartplotter. The problems, however, were many. Perhaps the most clear-cut was cost: even with the heavy discounting that was going on in early 2008, getting anything like a decent screen size involved spending more money than I now had left to play with.

Then there was the question of integration - I was fed up to the back teeth with Raymarine, whose instruments are actually quite good but who didn't appear to give a XXXX about compatibility, whether backwards with their older product or with third party equipment. I just couldn't face another round of problems with integrating more instruments, I wanted a standalone solution.

In addition, most fixed plotters came with a range of functions that looked wonderful in the advertising blurb but which I could only imagine would either never be used or would enslave their owners to disproportionate amounts of time spent onboard in front of a glowing screen; not my idea of boating fun - in contrast, I wanted something simple as well as cheap. Finally, one might well argue that all that cash spent on a chartplotter was OTT on a yacht whose owner's greatest sailing ambition so far had been to make it Round The Island in one piece and in broad daylight.

In short, I wanted a chartplotter like I'd want, say, a Ferrari. But no way did I need one, and still less could I justify the expense. In any case, Arabella already proudly possessed not one, but two handheld chartplotters - a Garmin 60Csx running Bluecharts and a Raymarine RC400 running Navionics Gold charts. Both worked perfectly well and usually spent their lives clipped to holders on the pulpit rail or stuffed in a jacket pocket, while being referred to occasionally. My only complaints about them were, firstly, that they had tiny little displays which occasionally required the user to squint myopically to make out exactly what was happening onscreen and, second, that trying to use them for fairly basic functions like figuring out a distance and bearing to a given point, or extracting a compass course to steer, was more difficult than it should be simply because of the fiddly little buttons and endless menus. On last year's RTI race, for example, we called the tide all wrong on the final leg because it simply wasn't that easy to extract the streams from the tidal 'diamonds' provided in either set of charts, and the obvious step of displaying streams onscreen or at least factoring them into a given course to steer didn't appear to have occurred to the designers of either the Garmin or the RC400.

Chart plotters use cartridges loaded with proprietary vector charts, like theNavionics and Bluecharts mentioned above. Although some people love vector charts, I can't help getting paranoid about what's being hidden from me in order to avoid clutter at different levels of zoom.

Above: screen shots of vector charts displayed on a PC screen (right) and a common or garden chartplottter (left).

I can accept vector charts as a fact of life on handheld plotters. If nothing else, the ability to declutter means that the chart remains legible even on a very small screen. However, I much prefer raster charts - scanned copies of real paper charts. Personally, when it comes to paper charts, I am a traditionalist and choose the Admiralty Charts produced by UKHO. These charts are available in digital form, as rasters, via ARCS.

Aside from the fact that few dedicated chartplotters currently display raster charts, the cost of the hardware, at the time of writing, is high even for an entry-level model. I would happily go for a basic model if it was just a matter of accepting that it had limited functionality, but unfortunately in the chartplotter world, "entry-level" is a euphemism for "tiny screen". In order to get a screen even remotely large enough to just glance at now and then, from the helm say, the sterling cost runs easily into high three figures.

On the other hand, if you already own a PC, and especially a laptop or notebook computer, you already have access to a decent-sized screen and a load of processing power. Moreover, PCs are well-served by software products that display raster charts and GPS data (and AIS, and GRIBs, and a host of other inputs if you want them). So it's entirely feasible to create a set-up that (a) has a big picture of (b) a 'real' chart, showing (c) your position on it.

My budget for this exercise was £250, barely enough to cover the cost of an individual vector chart cartridge, depending on the brand. That budget was somewhat arbitrary, but with the big bills of Arabella's refit behind me, the objective was to find a (cheapskate) way of using my existing laptop for chartplotting - preferably without having to interface it with the onboard instruments, and simply using a plug-and-play GPS antenna - at a capital cost that was remotely commensurate with Arabella's market value of, um, not very much.

There was one immediate snag. My laptop is a MacBook Pro. A wondrous piece of kit, but not one with an embarrassment of riches when it comes to finding compatible navigation software or compatible GPS units.

My list of things to sort out at the planning stage therefore boiled down to the following:

• locate Mac-compatible nav/chartplotting software for raster charts


• locate Mac-compatible GPS receiver


• figure out how to handle the laptop's power demand


• work out how to mount the laptop securely below decks, if possible in such a way that the screen could be visible from the cockpit

Mac-compatible software

Essentially, at consumer level, Mac nav software comes down to two-and-a-half choices. In one corner you will find GPSNavX and its bigger brother MacENC. They represent one-and-a-half of the options. The alternative is PassagePlus. All of these products envisage that you will plug a GPS into your Mac in order to convert it to a real-time chartplotter, and also provide the option to connect up an AIS receiver in order to display ships' AIS information directly on the chart screen.

None of these products are especially complex or sophisticated to use by comparison with the equivalent PC software. The GPSNavX/McENC pairing have been around longer, have been developed further and therefore offer more features than PassagePlus. That also means they are tougher to get to grips with.

GPSNavX displays only raster charts. Its bigger and more powerful sibling MacENC can display vector charts if required. PassagePlus displays only raster charts - in fact it was originally developed as a means of enabling Mac users to display Admiralty ARCS raster charts. Which is how, as I searched for a way of using ARCS charts, I came to stumble across it.

At various times, I had downloaded and played with demo versions of GPSNavX and PassagePlus. I'd be the first to acknowledge that GPSNavX has lots more features and is undoubtedly the technically more advanced program. But (a) it doesn't work with Admiralty charts and (b) this is just personal, but I didn't like it as much as PassagePlus.

The thing about PassagePlus is this: it's just so darned simple and intuitive. When you start it up, a slick, professional-looking interface appears - that just doesn't do very much. Within 10 minutes, I sussed out all that it could do and how to make it do it. Now for the power user, I'm sure that's all very boring and amateurish. But for a simple yachtie, this program is a dream. Here's what it does:

• display chart


• display GPS position of your boat on chart (if GPS is connected)


• display related data, e.g. COG, SOG, DTW, etc


• display AIS data as an overlay on the chart (if AIS receiver is connected)


• import/create and store waypoints


• import/create and store routes
  


• show track (assuming GPS is connected), save it, export it (for printing, etc)


• show bearing and distance between two points on chart


• use it for dead reckoning and three-point fixes without a GPS


• shapes a course to steer allowing for leeway and tide


• projects your position forward based on your current course and speed


• automatically creates a log - like the page in a log book - of where you were and when (assuming GPS is connected)


• and that's it, basically

I am not remotely embarrassed to say that this list covers everything, if not more, that I ever do or want to do with regard to navigation. It doesn't overlay GRIB files or anything clever like that, and nor do I want it to. It just does what used to get done on the chart table at the nav station, only electronically.

Being simple and having lots of big buttons, PassagePlus is also incredibly quick in use. Just point, click, and you're done. No fumbling with complex commands or menus. No split screens. No head-up or North-up decisions. Point, click and you've got the answer.

Above: PassagePlus in DR mode, showing track and estimated position. The software 'tracks' the boat as if the GPS was connected, except that it is doing so on the basis of course steered, speed and leeway as input by the user, and taking into account tidal set from the diamonds on the Admiralty chart. Below: Setting a magnetic course to steer in PassagePlus - click on chart, then drag and click to where you want to go. (Images from PassagePlus website).



Whoever developed PassagePlus has put a lot of thought and care into it. It isn't basic merely because it's cheap (it costs around £35 - but then so does GPSNavX, which has loads more features). It's basic by design, and as a design it elevates being basic to an art form. It's basic but classy. And I love it to bits. If you have a Mac and you're wondering whether to try using Nav software, do have a go with it. You can download a free demo copy, and sample charts to play with, by going here.

Mac-compatible GPS

Macs being Macs, they don't necessarily make it easy to connect to a GPS receiver. Of the major handheld brands, Garmin are probably the most Mac-friendly and do at least have an active policy of developing Mac-compatible hardware and software. They still have a way to go though, and if you intend to connect a Garmin to your Mac, as at the time of writing, you will still need a serial-to-USB adaptor and, depending on the age and type of your GPS unit, additional software loaded on your Mac.

In my case, I wanted the laptop chartplotter to operate as a standalone unit below decks and to keep using the Garmin handheld out in the cockpit. The issue was then to find a separate GPS receiver that would definitely-not-maybe work with a Mac, out of the box. The shortest of Google searches revealed one receiver that was consistently recommended in a raft of reviews, not to mention extremely good value: the GlobalSat BU-353. This is a WAAS enabled, waterproof design with a magnet to make mounting easier, and a 5 foot cable which meant it could be left on the cabin roof while still being connected to the laptop below.

Above: GlobalSat BU-353 USB waterproof GPS receiver.

Critically, the BU-353 is built specifically for the Mac and comes with a USB conector and the serial-to-USB convertor is actually built into the unit - so it really is just plug-and-play. At £33.00 it was a steal, and when I got it home and plugged it into my MacBook, the BU-353 worked first time, finding a fix very quickly from a cold start. Consistent with the simplicity of the PassagePlus software, it took me three minutes to figure out how to set up the software to receive the signal from the BU353 and almost before I knew it, there was my position, plotted accurately on the screen.


Power supply and consumption

Ah, yes. Not my specialist subject. I had to hit the books again, but this is where I ended up. (By the way, before you trust what I say on this topic, you might want to review the disclaimer in this earlier post about onboard power).

Assuming I was actually sailing somewhere when using the laptop as a chartplotter, then pretty clearly I'd need to feed it some electricity. And the obvious source of that power was the 115A ship's battery. Laptops like DC power, which is good, because once Arabella sets sail, DC is all that's on offer from the onboard electrical system.

My MacBook Pro was rated at 18V DC, 4.6A maximum. That gave a wattage of 83W (Watts = Amps x Volts). The power cable for the MacBook was rated for up to 85W, however, and that's the number I used for the purposes of my calculations, which erred on the side of caution. I have no problem with being delighted to find I have a bit more power than I thought I had; the reverse, however, does not apply.

Now the rated DC consumption of 85W, 4.6A was at 18V DC, but Arabella's system is 12V nominal. It was necessary to twist the basic formula around to get Amps = Watts/Volts, in order to see what a difference that made. It gave a result of 7 A (85W/12V). Quite a lot more power consumption than the 4.6A mentioned above.

The best result I could hope for would be to run the laptop straight from Arabella's 12V (cigar) socket, perhaps using one of those airline seat socket "Enpower" cables with a 20mm (cigarette lighter sized) adaptor plug on the end. Apple did produce and sell such an item. However it had been tested by many other people and found not to work except in, um well, airline seat sockets. In fact, Apple carried a cautionary notice on their website to inform buyers of this inconvenient fact, and stop them buying the cable for any other purpose. That was a shame as I already owned that cable and was hoping to shave a bit off the budget by relying on it, but after testing it I could confirm that Apple were quite right. The Enpower cable didn't work in car and/or boat 12v sockets.

The reasons for this were obscure but I saw the theory advanced that the MacBook required at least 16V DC before it would even think about doing anything. That was safely within airline/Enpower voltage parameters but pretty clearly not within those of the typical boat's 12V system. My battery, for example, never exceeded 12.8V when 100% charged, and I'd never watched the meter especially carefully when the shorepower was connected and the charger was switched on, but I had seen it go as high 14.6V in such circumstances. (There is another theory, which is that more recent Mac laptops contain sophisticated circuitry that detects when the 'wrong' power cable is being used and, in order to protect the computer, prevents it from functioning).

If I wasn't committed to a Mac, I could shop around for alternative (non OEM) suppliers of 12V cables. However, the "Magsafe" tip that connected the power cable to the MacBook's power socket was proprietary to Apple and had not been licensed to aftermarket manufacturers. So there was no alternative provider.

Unless, that is, one turned instead to an inverter. An inverter converts 12V DC power to 240V AC power and has a normal 240V socket in the side, which meant I could just plug in the MacBook using its normal power cable.

Kensington made an "Ultra Portable Power Inverter 150", which was recommended by Apple (useful as a starting point for arguing about who's to blame if the inverter blows up your sole laptop), so that's what I went out and bought for £50. As the name suggests, it's small, light and rated up to 150W, which gives a considerable margin of safety over the MacBook's maximum 85W. Moreover, because the inverter outputs power via a conventional three pin AC socket, you can also plug in lots of other items, such as mobile phones, battery chargers and so on, using their normal charging cables.

Above: Kensington Ultra Portable Inverter 150 (UK models have a standard British 3-pin 240V socket built into the 'black box', instead of the version shown here).

Inverters themselves consume relatively little power, so in essence an inverter's power consumption depends on what's been hooked up to it. If you use an inverter to power a microwave on board, clearly there's going to be a pretty big draw on the battery bank. A laptop in contrast is more modest - in fact 7A as mentioned above, in the case of my laptop.

So far, so good. However, there is a 'but'. All that converting from DC to AC and back again to DC (via the laptop's own power adaptor) does have the effect, naturally enough, of introducing some inefficiencies into the process. It's unusual for an inverter to beat 90% efficiency. In addition all that cable the power has to run through adds to the loss in efficiency - as a rule of thumb, that's another 10% wasted. These inefficiencies can be dealt with, for calculation purposes, by adding both their percentages to the wattage of the appliance that is connected. In the case of my MacBook that meant adding 20% in total to the rated 85W, making 102W. On the application of the above formula, that produced a draw of 8.5A - an increase of 1.5A over the estimated draw via a direct (DC-DC) cable.

(Interestingly, a well-used rule of thumb states that for every 100W of power output, an inverter draws 10A from your 12V battery - which in the case of my MacBook gave the same result: 8.5A).

Having established that powering the laptop via an inverter plugged into the 12V socket resulted in a draw of 8.5A per hour, it should be remembered that Arabella carried a single 115A battery. That didn't give a lot of capacity for hours and hours of laptoppery at 8.5A. In fact after just seven hours, that rate of power consumption - when taken together with the combined draw of the instruments and VHF, and offsetting the charge input from the solar panel - would have drained the ship's battery down to the crucial 50% charge level below which one should aim never to go. And that was in daylight on a bright day, where the solar panel was actually sticking some charge back in. The drain would be worse at night.

Equally, the MacBook did of course have a battery all of its own. In fact, in my case, it had two batteries, because I had stumped up for a spare at the time I bought the laptop itslelf. Mac laptop batteries are frequently derided for their poor performance against Apples' marketing claims. To listen to Steve Jobs, you'd think a MacBook would run for six hours off its battery. Back in the real world, I found that I would get three-and-a-half hours' life out of the battery, less for power-hungry task like playing DVDs. Still, three or more hours battery life (twice) added to the seven (daylight) hours that the ship's battery could safely provide gave more than 13 hours continuous operation.

And there was another interesting little fact: when the MacBook was plugged into the inverter, the power supply didn't just run the laptop. It also charged the laptop battery, the same as plugging in it at home. In contrast, the direct (DC-DC) airline/Enpower cable didn'tcharge the battery, even when used in a situation in which it worked at all. In fact many such cables don't charge the laptop battery because they can't kick through enough juice. So using the inverter, while more costly in terms of draw on the ship's battery, also gave something back - at least one fully charged laptop battery. Which added a further three hours to the 13 hours mentioned above - 16 hours' total endurance. Make that 19 hours, if the inverter was left running - could be left running - for long enough to charge both batteries.

It didn't do my 24 hour + rule any favours, but it was more than sufficient until I had the patience, let alone the budget, to rethink Arabella's battery arrangements.

Mounting the laptop onboard

Quite a few people seem content to leave their laptops perched on the nav table, sitting on a non-slip mat. Others glue velcro to the table and the laptop, and ensure the two are introduced to one another. Neither approach appealed to me - Arabella is a little boat that bounces around a fair bit, especially when my lunatic racing crew get their hands on her. I couldn't see my laptop staying put very long under such conditions. I wanted a proper mount, and I wanted to be able to swivel the screen so that it remained sheltered from spray but was visible from the helm.

Unless you have something fabricated to order (too costly) or have the skills to make a mount yourself (I don't), there are not too many options. After some research, I alighted on a RAM Laptop Tray combined with an articulated double swing arm. At £125, this was not a cheap option, and when it arrived, it seemed both huge and ugly.

Above and below: RAM laptop tray and double swing arm mount. Not the prettiest things in the world, but very, very strong, secure and versatile.

On the positive side, the contraption looked a lot better when it was mounted in situ, and it was also hugely strong and secure. In addition, it could be removed from the bulkhead and stored away when not in use, although in fact once it was mounted it didn't look all that intrusive.

Siting the RAM mount on the rear bulkhead, it seemed doubtful to me whether the GRP could actually support the combined weight of the laptop and mount. In the end, I played it safe and through bolted the RAM mount, with wooden backing plates on both sides of the GRP. This resulted in a very strong and secure installation.

The beauty of the articulated arm is that it enables the laptop to be placed in a wide range of positions. It can be pushed back under cover if conditions demand, or it can be swung round so that it is visible from the cockpit. It does pay to keep the companionway hatch pulled over, though, partly to shade the screen for better visibility and partly to shelter the laptop from spray or rain.

Costs

I mentioned earlier that I set myself a budget of £250 to kit Arabella out for laptop navigation. In the event, I overshot and spent £335, largely because I had failed to take into account the costs of (a) powering and (b) mounting the laptop on board. Those two items alone came to £175.

In contrast, the necessary software and GPS unit were both, I thought, very good value at £35 and £33 respectively. I didn't expect these items to come in at such a modest total of £68.

The ARCS charts were not especially cheap at £90 for the Solent portfolio. Certainly if you stop and think about the geographical area covered by a typical vector chart cartridge, the higher cost of the cartridge seems to me to be good value per square mile covered by comparison with ARCS charts. But that cost differential is somewhat offset by the fact that ARCS charts can be digitally updated by CDs issued by UKHO for a modest annual subscription, whereas I have never found a realistic way of updating a vector chart cartridge - it seems you just have to buy a new set of charts every so often.

Mounting the laptop securely was a major expense, but ultimately I only owned one laptop, which had to serve all my home computing needs. I didn't want to be breaking it, no matter how religious I am about backing up my data to an extenal hard drive.

Did £335 represent good value for money? I thought so. At the time, a Raymarine dedicated plotter with a smaller screen - albeit water-resistant and fully-interfaced with the other instruments - would have cost anything from £395 up to well north of a grand. There were cheaper brands, such as Navman, which went down to below £300, but again they used vector charts and had tiddly screens.

My MacBook, in contrast, lacked a full interface with the onboard instrumentation - but then, I wasn't looking for one - and had to be kept below decks in order to protect it. However it had a relatively big and very clear screen, and it could be swiveled on its mount so as to be visible from the cockpit. Plus of course it was a computer, which meant it could do what computers do: go online via a wireless connection or 3G dongle; send and receive emails; play music and Tv shows off iTunes; play DVDs; process photos; run videochats using the built-in camera and Skpe; and all the rest.

The system in use

So far, I have only used the system once when out sailing, but it worked just fine. The RAM mount positions the MacBook nicely inside the companionway, under the shelter of the main hatch and, as the picture below demonstrates, the screen is clearly visible from the helm even in bright light.


The MacBook Pro ran on its two batteries for well over five hours (at which point, it was switched off with 25% remaining on the second battery). Not needing to recharge, I used the inverter solely to power the laptop while hot-swapping batteries. That went fine.

The PassagePlus software and BU-353 GPS receiver worked smoothly throughout, providing SOG and COG data that correlated to that displayed by the onboard system (Raystar GPS and ST60+ Graphic Display). The track was uncannily accurate - see for example this detail from a screenshot, showing the point at which, outbound, we rounded up into the wind to raise the main before resuming our course down river.

Above: the little loop on our outbound track shows where we rounded up into the wind in order to get the main up. Note also the little purple arrow, next to Tidal Diamond B, showing real-time tidal current.

All in all, one satisfied customer at the fraction of the cost of a dedicated plotter. Not to mention that watching Desperate Housewives on iTunes while short tacking back up the river on the way home is one of those experiences that surely not even the new Moody can give you...