RTIR '08: not our year

Arabella retired less than two hours after starting this year's RTIR. After struggling to claw our way to windward and falling further and further back in the fleet, and with a stream of distress broadcasts emanating from the fleet in front of us as it encountered reasonably challenging conditions at the Needles and St Catherines Point, we chose to cut our losses and pulled into Yarmouth to wait for the tide to turn.

Above: It was nice of them to send Oceana to see us off from Southampton so early in the morning.

With F4-5, gusting F6, and wind against tide conditions, Arabella made a good start but we were soon struggling with short, sharp waves that continually halted forward progress. The waves were not especially big, but we took a significant amount of water over the top and much of it found its way below decks, especially via the forehatch, which will certainly need (yet) another looking at.

It was difficult to put into words, but we could all sense that Arabella was struggling - not with the conditions generally, but with being relentlessly driven as close to windward as she would point. If she was allowed to fall off the wind a little, Arabella would sail comfortably and fast - and stay dry - but that was no way to win our class, and although we caught some of the weaker members of the class before us, a much larger number of our own class were pulling relentlessly ahead.

Above: Our track down the West Solent, up to the point where I disconnected and stowed the laptop to preserve it from the ever-increasing amounts of water entering the cabin. We took the decision to retire soon afterwards. Screenshot taken from PassagePlus software (click the image for larger view).

In addition, in that early stage of the race, a continual stream of distress broadcasts came from the main body of the fleet ahead of us, with boats dismasted and men overboard (11 people went into the water on the day).

As Newtown came abreast, I nipped below decks to see what if anything could be done about the ingress of water. It wasn't particularly alarming, but in a small boat like Arabella, there aren't that many dry places left to stow things once their usual homes get soaked. One of the lifejackets had self-inflated, which would make it difficult if not impossible to use if needed - not a problem in itself as we had four on board and only three people, but we wouldn't want to be losing any more if we could help it. To be on the safe side, I also disconnected the laptop and stowed it somewhere waterproof, no sense in losing that too, given that a reasonable amount of water was shipping through the companionway having traveled the entire length of the coach roof.

The part of me that was still being analytical - as opposed to hanging on grimly so as not to be flung bodily up and down the cabin - noted that sea water entering via this route had also entered the locker where the battery was stowed securely. It hadn't reached a level high enough to do any harm yet, but it was swilling round the base of the battery and clearly, with this degree of motion, the risk was that it slopped up and shorted the connections. That was going to need seeing to, as well as the forehatch.

As Yarmouth Pier came into view, there was a hurried consultation. This was clearly not going to be our day, the racing conditions at least were borderline for Arabella, and many long and unrewarding hours lay ahead. We could press on, and risk damaging the boat, or we could dive into Yarmouth and wait out the tide for an easy, downwind return to Southampton. It wasn't a difficult call, and before long, Arabella was tucked up snugly on the walk-on pontoons at Yarmouth while we availed ourselves of the hospitality of the George.

Above and below: Snugged-up and drying out in Yarmouth Harbour.

A variety of retirees came into Yarmouth while we relaxed and dried ourselves out. Saddest of all was a little red Sonata that had been dismasted. More than anything, that helped to persuade us that pulling out was the right call for us at least. Arabella can be a tough, speedy little thing, but she needs the right conditions, and pounding to windward is not her forte. That afternoon, as the flood tide, now with the wind gusting up to 26 knots, created smoother if rolly conditions, Arabella went on to demonstrate what she is capable of, with some superb downwind surfing on a speedy trip back home.

Not our year in the race, then, but the sleigh ride home gave us some of the fastest and most exhilarating sailing yet under hot sunshine and cobalt skies. And the West Solent was almost entirely deserted. Again. Wonderful.

Conditions: SW F5-6 Heavy overcast early, sunny later. Sea state moderate, occasionally rough
Distance covered (GPS over ground): 37.9 NM
Total distance covered to date (2008): 70.16 NM
Engine hours: 2.5 (total for 2008: 6.2)

Another lesson

The forecast had steadily improved as the date for my next lesson with Roger drew near. The threat of rain disappeared on the preceding day, and there was even a suggestion that there might be sunny spells. This being England in June, the latter turned out to be wrong, but I was happy to settle for merely dry.

The only worrying aspect to the forecasts - and worryingly consistent they were, too - was the threat of winds gusting to 38 knots. By the morning of the day itself, the Met Office "Marinecall" forecast was even threatening F7 by midnight.

Which was all a bit worrying given that we were due to cast off at 1530...

I reached the marina an hour or so early, expecting to find the tide in full ebb. But the tide remained obdurately high, no doubt as a result of the low pressure and the strong winds blowing up the river from Southampton Water. The marina was, as ever in strong winds, an unnerving place to be, halyards frapping and the wind whistling through the rigging.

Roger arrived dead on time, at which point the water level had changed not at all, and we opted to get going quickly before the ebb suddenly realised it hadn't started and decided to pour out in the one-and-a-half hours that the tide tables said it had left to do so. Pretty clearly we were going to need to reef down. I suggested putting one reef in the mainsail; Roger recommended two, and as it turned out, his was the right call.

The immediate objective was for me to leave the marina singlehanded, and then to gather in the mooring lines and fenders alone while keeping Arabella under control. In stark contrast to the last time I had tried this, I executed a clean exit from the berth, using a spring from the end of the finger pontoon to my starboard quarter to help swing Arabella around and then, helped by the wind, motoring out into an empty river.

The ebb had set in here, with a vengeance, and wind over tide conditions created a steep, short chop. I was all set to motor down to Southampton Water before leaving the helm to attend to the warps and fenders, but Roger stopped me. "Why don't you do it here?", he asked, "Just motor out into the middle of the river, knock the engine into neutral, and see what she does?"

That hadn't occurred to me. I did as Roger suggested and, to my surprise, Arabella more-or-less held station, her stern at 45 degress to the wind, which gently nudged her against the fast-flowing spring ebb. Eventually, she would run out of "sea" room, but not before I'd had more than enough time to sort out the warps and fenders, which I proceeded to do.

"You might as well get the main up, then," called Roger from the cockpit, "Let off the mainsheet and get the sail up, she'll weathercock into the wind gently."

I did as Roger suggested, and sure enough, so did Arabella.

"Okay," said Roger, "So, let's take stock - you're now all ready to motor off down river, and you've got everything done not fifty yards from your marina berth. I'm not suggesting you'd want to short-tack down the river on your own in these conditions, but on a calmer day with the wind from the right direction, you could be unfurling the genoa right now and sailing off."

As usual, he was right. We decided that was enough pretend singlehanding for a bit, and unfurled the genoa anyway, and short-tacked our way down river and out onto Southampton Water. Arabella's rigging had - finally - been adjusted by the on-site riggers at the marina. There was a noticeable improvement in her pointing and powering ability, even with two reefs in the main.

Once we were safely past an out-of-control fleet of kids in Laser Pico's, shepherded with increasing desperation by a teacher in a rib whilst being blown this way and that by F6 gusts, I suggested a coffee.

"How are you going to do that singlehanded, then?", countered Roger. Creative to the core, I suggested handing him the tiller, but it turned out the correct answer was to heave to. A very long time ago, I'd been taught on some RYA course or other how to do this, by in essence tacking but leaving the genoa sheeted in, so that it backed, then putting the tiller to leeward. I was also dimly aware that heaving-to was a good technique for long-keeled yachts, but not for fin-keelers, and I had no idea what a twin-keeler like Arabella would do. Still, nothing ventured nothing gained. I did as Roger suggested, and as Arabella hove to with surprising ease in the gusting winds, gently forereaching at a fraction of a knot.

Above: Heaving-to (image "borrowed" from http://www.sailtrain.co.uk - hopefully they won't mind in return for the free link)

Once recaffeinated, it was off for an exhilarating sail down to Hamble and back, before goosewinging our way upriver to the marina and another successful docking singlehanded at about 2030.

The news got even better about halfway through, when the log impeller, which had steadfastly refused to free itself last time out, suddenly whirred into life and gave us a speed reading.

This was the third midweek day that I had been out sailing in four weeks. To be fair, the weather hadn't been perfect on any of them, and today certainly, anyone sat undecided in a marina would have been understandably deterred from going out by the sound of the wind howling through the all that rigging. But across those three days, I had seen a total of fifteen yachts out, as well as a smattering of dinghies. Amazing. It was nearly midsummer, and we had the Solent all to ourselves.


Conditions: WSW F5-6. Heavy overcast. Sea state slight, some chop.
Distance covered (GPS over ground): 13.4 NM
Total distance covered to date (2008): 32.26 NM
Engine hours: 0.5 (total for 2008: 3.7)

Practice for the Round The Island Race

With about a fortnight to go before this year's race, I went out with another member of our three man race crew (our giant-slaying line up remains unchanged from last year's race) to try out the new spinnaker from Sanders Sails.

Above: To view all Arabella's vids, click HERE.

I have a bit of a hang-up about spinnakers, having seen some years ago what they do when they're allowed to take control. But I also had to bear in mind the wishes of Arabella's racing crew, who had become pretty frustrated on the RTIR last year - when conditions demanded a spinnaker and I was only able to offer a cruising chute. On the basis that a spinnaker might get used, at most, a couple of times per year, I had now splashed out on a full radial racing jobbie, made to order in 0.75 0z. premium nylon.

Before we could go off and play with our new toy, of course, I had to have one my now-customary encounters with what passes for 'customer care' among the businesses on site at Arabella's marina. The now-defunct boatyard company had supplied the spinnaker pole without a bridle. A brief visit to the riggers elicited much sucking of teeth when we asked if they could rig up a wire bridle for us in the next couple of hours. Maybe next week, they said, or else there was another rigging company just outside the marina gates. Anyway, they said, a tiny little pole like that didn't need a bridle, we should just lead the uphaul and downhaul lines to one end of it. I wondered about asking how they thought we could gybe the pole end-to-end with a set-up like that, but in the end decided that I probably wouldn't get a sensible reply. I did make a mental note to look into the riggers just off-site, though...

In the end we rigged the bridle ourselves, using the least stretchy lines we could find, and some metal rings bought from the chandlery at about 4 times the price they probably should have cost, and - some hours later than planned - off we set.

It was one of those days when the weather can't seem to settle, with periods of hot sunshine punctuating longer spells of heavy cloud and light rain. On the way out we passed a singlehander making his way back in. He grimaced as we came abreast. "Gusty," was all he said. He wasn't wrong. Some of the clouds were low and dark, creating wind conditions that were not only gusty, but fluky as well, as if the wind couldn't decide which side of north it wanted to come in on.

In the circumstances, we picked our moment to fly the spinnaker with some care. A reasonably sizeable patch of blue sky opened up overhead, and we took our chance as the breeze fell off and settled more or less northerly.

It was fortunate that, in the process of working out dockside how to rig the spinnaker and pole, we had already set up the sheet, guy and a Heath Robinson-esque adjustable downhaul for the pole, so we were all set to go when the opportunity presented itself. Sanders Sails had provided a launch bag, which also helped the process of setting the sail up for launching somewhat. The best place for it appeared to be on the leeward deck, amidships, clipped to the guardrail.

Following the skipper-elect's instructions, I managed to hoist the sail without undue drama, while he trimmed from the cockpit.

We only managed a short run with spinnaker up, due to the changeable conditions, but it was long enough for me to grasp the basics and it did wonders for my confidence with this sail, which I find a bit fearsome. I still wouldn't say I was a fan, exactly, but I did get that bit more comfortable. Perhaps more importantly, Arabella put in a serious turn of speed, even with a breeze of only F2, at that particular moment, filling the spinnaker.

Above and below: Ready to launch from amidships.

All too soon, even before we had the chance to practice gybing the pole at sea rather than dockside, it was time to drop the spinnaker as the next wave of clouds rolled in and the wind began to build once more. Again, following the slipper-elect's instructions, I stood in the companionway, released the spinnaker halyard to run freely and, as quickly as possible, gathered in the billowing nylon on the sheet, under the mainsail, pushing it down into Arabella's cabin where it could be repacked. Then it was up on to the foredeck to unrig and stow the pole, as the genoa was unfurled and we turned and headed back for home.

Below: As with the practice run for the race last year, so it was again this year - the log impeller has become fouled barely four weeks after going back into the water, hence the row of big fat zeros on the instrument head. At least the Mac Chartplotter was working.



We enjoyed a fantastic beat back up Southampton Water. On the helm, I kept Arabella sailing on her ear, keeping her port bow dipped well under, in the hope that the turbulence might free up the log impeller, which appeared to be fouled again. All in vain, unfortunately.

With a rising wind and a fair tide to help us on our way, we fairly flew back to Dock Head, before short-tacking upriver to the marina and a well-earned pint.

Below: Where we went today. Screenshots taken from PassagePlus software (click each image for larger view).




Conditions: N, NW and NE F2-5. Mixed sunshine, cloud and rain, some thunder. Sea state slight.
Distance covered (GPS over ground): 13.7 NM
Total distance covered to date (2008): 18.86 NM
Engine hours: 0.6 (total for 2008: 3.2)

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...