The Offshore Voyaging Reference Site

Limits To Complexity

We are now at the final stage of selecting our navigation systems, and as new products are being launched all of the time, have decided to wait until the last minute before committing.

But to some degree the choices are being made for (or taken away from) us, as so many of the manufacturers are moving towards integrated systems, reducing the available options for those of us who like to pick and mix the best kit from different stables. For example, it is now virtually impossible to buy a stand alone radar, as everyone is moving towards combined radar/plotters using their own Ethernet type connectivity.

Since the 90’s I have professionally skippered my own yacht on research projects, and have for the last six years used a laptop linked to a GPS for all basic navigation. Being only modestly computer literate has never been a major shortcoming, and although they have simply been fixed to the chart table with Velcro, we have never lost one to damp or rough handling. If you are used to computers at all, they are quick and intuitive to operate, and their large screens offer a good view of the charts. By comparison, I recently skippered a boat with a brand new plotter, and didn’t like it at all—the screen was too small, and the operation was clumsy and slow. And having recently watched two experts trying to sort out a problem aboard a boat with an Ethernet link between instruments and plotter—two sets of software, and by their own admission, a tendency to crash on a regular basis—I wonder whether this is really the way forward?

Of course PCs can go wrong, too—we carry a spare as back up, as well as up to date passage charts and pilot books, just in case. And as I learned to navigate long before we had any electronic luxuries, if I have to go back to dead reckoning in an emergency it should not a big deal. But with our laptop we can integrate weather files from the internet, AIS information, tidal streams and Navtex at far lower cost than a half way decent plotter. And we’ll stick with an NMEA interface which at least will allow some basic diagnostic tests to be run should it go down 1000 miles from the nearest dealer.

The one thing we have committed to is an Echopilot forward looking echosounder. We used an Interphase Twin Scope for the last seven years, and found that the ability to scan for depth and obstructions ahead of the boat was indispensable, especially in poorly charted waters. But Echopilot sensibly offer the option of a custom transducer housing made from solid aluminum billet (essential for us with our aluminum hull) which will enable us to pull the transducer prior to taking the ground, one of our main reasons for choosing an OVNI. Having heard nothing but good reports of their products, this was an easy choice to make.

And while we’re on the subject of holes in the hull, we think the fewer, the better, so we’re not having a through hull speed/log unit. Paddle wheel logs are unreliable, and often tricky to calibrate accurately, and as a Furuno WAAS GPS reads speed as fast as a log, we shall use a repeater in the cockpit as a speedo, and the trip facility as a log. We are well aware that this is “over the ground”, but we can compensate for that if needs be. And if all of the electrics fail, then we have a lovely boxed Walker Knotmaster towed log that has followed me from boat to boat over the years. There should be a limit to complexity!

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I welded up my speed log hole for the same reason, haven’t missed it yet…

How do you like the Echopilot?

Colin Speedie

Hi Ben

The Echopilot is good, but not as sophisticated as the Interphase TwinScope unit we had on our last boat. But Echopilot make a custom aluminium transducer housing, which was far more suitable for installation in our aluminium hull, which wasn’t an option with an Interphase unit.

But the principle of these units is great, and for nosing your way into rivers or shallow anchorages they are a real benefit.

Best wishes


John Harries

Hi Ben,

We have had an Echopilot for some 15 years. First an FLS II and now a Platinum. We would not be without it. It really takes the uncertainty out of being off the charts in the high latitudes.


Does anyone have experience with cockpit repeater screens for PC based navigation systems? I have a pair of IBM t42 magnesium case PCs that I bought for $200 each. More than adequate capacity and speed, and cheap redundancy. Sure would be nice to have a full function cockpit display though…

Colin Speedie


We tried a Panasonic Toughbook tablet as a repeater in our cockpit on our previous boat. It worked fine, but had its limitations, and was a very expensive option, but our principal use for it was data recording.

Once decent quality waterproof screens become available at a viable price I think they will be the future – I wish we had stuck with our previous PC based navigational system.

Best wishes


John Harries

Hi Colin,

We have been using a Tflex-G615XL 15” Sunlight Readable water proof display for the last two years. So far it has been great. Not cheap at $1500, but a far cry from the $4000 plus that other vendors wanted for a waterproof screen. The cost for the screen and the Dell laptop driving it were not much more than a good plotter. And, if we take into account that we would need the laptop even if we had a plotter, we see our system as a veritable bargain.

John Harries


We have used a cockpit repeater screen running off a laptop below for the last two years and are very happy with it. For all the details, see this post.

Neil McCubbin

We have used PC-based navigation and radar for 12 years, and have sailed on several boats with dedicated plotters.
We MUCH prefer the PC. Presently it is an ASUS 1L which runs on 12 volts directly, and draws 1 amp (specs say 3, be we do not see that) The display is a Dell 21″ that draws 4 amps, through an inverter. Resolution is as good as the latest plotters, although the screen is 12 years old. We like the large size.
We have loads of backup with two laptops, an iPad, an old Garmin 286 handheld with 12 volt power option, and often crew laptops too.
I have yet to be on a boat with a full backup for the chart plotter.
The Asus is limited to XP, and is slow by todays standards. We will probably replace with an “all in one” screen/computer with today’s quality resolution.
Apart from the lower cost of the PC, the ability to find parts anywhere is appealing.
A further advantage of the PC/iPad hardware, is that we have a variety of software in the event that our mainstream Nobeltec goes funny. With a plotter from, say Raymarine, I would worry that a software upgrade would have a bug, discovered as sea, that prevented operation.

John Harries

Hi Neil,

I would agree, we too have had good results from a PC based system. Here is an in-depth post on it and some of the tradeoffs:


How important do you find it to know the current you are sailing through. Can it be calculated without a speed-through-the water sensor AND a GPS?

John Harries

Hi Paul,

Good question. I really like to know what the current or tide is. And no, there is no way to do that without a speed through the water sensor.

Marc Dacey

Wait a minute, you can calculate for set and drift and even figure out vectors by setting a course over ground on an autopilot to a given waypoint and then figuring out tidal effects by how much you “miss” your intended arrival? Your offing and your heading sensor (or a close comparison of your “crabbing” versus your course to get to your intended arbitrary spot) can tell you reasonably well if tidal and current are present and to what degree. It’s just observation, like a running fix, no?

John Harries

Hi Marc,

Yes, you can do that, but it’s no where near as useful as being able to just look at two dials and subtract one from the other to see how much current here is.


Hi John,

this holds true only if the current is straight with you or against you which I believe would rather be a seldom event, except driving up a river, of course. On the other extreme, current coming almost perpendicular but slightly ahead to your course, you wouldn’t see any difference at all between the dials, and notice it only on the plotter.

John Harries

Hi Ernest and Marc,

OK, I do know how to navigate and DR and I do understand current vectors and in fact did that for years before any sort of electronic positioning was available. All I said was that I like to have both speeds over ground and through water and I answered the original question in the spirit of which I think it was asked…without writing a book on DR.

In fact if we couple a through the water speed sensor with a heading indicator and a GPS and we can have continues read out of current direction and speed, assuming all is calibrated well. That said, I have never bothered to do all that, but if I was still racing I sure would.

Maybe we could end it there.

Marc Dacey

Ernest has expressed it succinctly. This is rarely an issue most places, but I recall in Brittany where the tides are high and the shoreline complex, using the vectors in the “Bloc Marine” reference (see was essential to constructing a time table for getting a free ride up or down inlets or rivers off the Bay of Quiberon. I would imagine the same holds for Fundy around the corner from your “base camp”, but I haven’t sailed there yet.


Hi John,
I was never questioning your navigation mastery, the vectors just came to my mind… but then, navgation is mainly with the eye when near a shore, and on the chart when offshore. Everything else would add to complexity, and thats just the topic of this book, so I apologize arguing in the wrong direction 😉

John Harries

No problem, Ernest. I just didn’t want to turn a relatively simple question into a long thread about DR and vectors. Also, I was probably a bit crankier than justified (tired after a trying overnight) so sorry for that.


Hi Colin, or John
“Paddle wheel logs are unreliable” – agreed, but do you have some experience with electromagnetic transducer types, such as the one from NKE (see here: At least they cannot be fouled by weed or so.

John Harries

Hi Ernest,

No, no personal experience. What I do know is that several manufactures have, over the last 20 years announced, and then retracted various sensors without moving parts, so clearly it’s one of those technologies that’s quite hard to do. That said, the developments in the last couple of years look good, so maybe it’s time to adopt the technology. I for one will not miss keeping a paddle wheel clean!