The Old Ways of Navigation

[yachtorion]

I'm working away from home at the moment so stuck in a hotel in Swansea. I just got a position fix out of the hotel window using a hand bearing compass to a nav buoy 2 miles out and adding in roughly how far I am from the harbour wall (not very) - overlaid onto google maps the resulting fix was more accurate than the GPS position on my tablet.

Admittedly the GPS would have been better if I wasn't in a hotel building with a lot of floors above me - but I still found it educational

What surprised me was Navionics seemed to have no way of providing compass variation data. Found it in another app (a dedicated compass) - but it seems an odd thing to be missing. Also if I'd wanted to draw more than one bearing line for a cocked hat I'd have been out of luck.

Paper charts still have some uses then.

 

[rob2]

Absolutely, when using GPS to navigate one still needs paper charts to plot the latest position and when in sight of land it is wise to take a look around to confirm the electronics are giving a believable fix. I well remember sailing in Greece when a Nato exercise was taking place. There was no navigational warning given, but each time a plane hove into view the handheld GPS advised us to change our course by 180 degrees! I wonder whether similar signal corruption is to be found in the firing ranges that make up half the south coast cruising area?

Rob.

 

[srm]

When running STCW, Electronic Navigation and Radar Simulation courses for merchant navy officers GPS was just one of the 'aids to navigation'. We expected students to check their GPS positions and keep a paper chart plot along with the electronic aids. If students failed to check the GPS it was quietly degraded until it became unusable. Groundings on the simulator can be very instructive.

I have measured GPS errors of over one mile while sailing, and have seen the GPS put my boat over 5 miles from the pontoon it was secured to. Admittedly, these errors were short lived (around 30 minutes or so) but it is well worth double checking in areas where your position could be critical.

 

[ghostlymoron]

I still mark my position on a paper chart at intervals. If your electronics pack up, it would be useful to know your position within the last hour.

 

[yachtorion]

It made me think about GPS accuracy. We're probably all used to our GPS being accurate to a few meters.... but it doesn't take much to decrease that accuracy to the within a few hundred meters that I saw last night. Made me think about pilotage and being careful never to trust the GPS alone for critical positioning. Will be making sure I have a few bearings on the notepad before I go anywhere tight now!

 

[prv]

I still mark my position on a paper chart at intervals. If your electronics pack up, it would be useful to know your position within the last hour.

As long as a) the positions you've marked straight from GPS were accurate, and b) you noticed the subsequent accuracy degradation and reverted to the chartwork.

Subtle reductions of accuracy are much more dangerous than the screen going obviously blank.

A radar overlay on a plotter is an excellent cross-check within 20 miles or so of land - as long as the radar picture lines up with the chart underneath it, you know at a glance that the GPS position is accurate.

Pete

 

[BrianH]

What happened to the ship's logbook? Doesn't every skipper keep an hourly entry with position while on passage any more? While I keep the relevant paper chart available I no longer mark it with the hourly position but enter coordinates in the logbook.

I have measured GPS errors of over one mile while sailing, and have seen the GPS put my boat over 5 miles from the pontoon it was secured to.

In the days before affordable GPS (not that long ago) how I would have loved to have had my position to within 5nm when closing the low and featureless Dutch coast after four days of light headwinds and being swept up and down the North Sea by varying tides that made DR so imprecise.

 

[[70521]]

Admittedly the GPS would have been better if I wasn't in a hotel building with a lot of floors above me - but I still found it educational

You have the wrong GPS, mine works 10 meters indoors.

I only used them to check my nav, collect and share data.

 

[Boreades]

In the days before affordable GPS (not that long ago)

Yes, and how quickly we forget these things. Wandering with the tides across the North Sea these days would probably attract the attention of HM's Border Agency (or worse). Likewise dead-reckoning in fog across English Channel shipping lanes?

Once upon a time, some of our ancient mariners took a 20 year apprenticeship, and had to memorise everything.

For each day, five items of knowledge are required of everyone, with no appearance of boasting, who would be leader. The day of the solar month, the age of the moon, the state of the sea tide, without error, the day of the week, the calendar of the feasts of the deities.

 

[rivonia]

We always plotted position on the chart all the time. We always make log entries. I thought it was standard practise?

 

[Triassic]

I think it's important to recognise and understand the abilities and advantages of each navigational aid you have available. If I had been using Google Maps I would have simply entered the hotels postcode.......

 

[BrianH]

We always plotted position on the chart all the time. We always make log entries. I thought it was standard practise?

Log entries, yes, but no longer the chart. Constantly marking the same chart - even in pencil to erase (never completely successful) with regularly repeated passages it becomes confusing. Charts are too expensive to keep replacing when the plotter and PC vector charts (OCPN) provide my main navigation function. The relevant paper chart is always laid out on the chart table however, together with the logbook.

 

[prv]

What happened to the ship's logbook? Doesn't every skipper keep an hourly entry with position while on passage any more?

I don't, I'm afraid. On passage (as opposed to coastal pottering about) I plot an hourly position on the chart along with time, course, and log reading - the idea being that I could work out a reasonable EP from the last couple of these if needed. I have a sort of navigational notebook which I use for planning, mostly working out tides across the Channel though I've also pre-planned a couple of intricate passages among the Channel Islands rocks. But I don't keep a logbook as such.

I've occasionally thought that an informal diary ("narrative log"?) would be nice to look back on, but I've never got round to actually writing one.

Pete

 

[Elessar]

Absolutely, when using GPS to navigate one still needs paper charts to plot the latest position and when in sight of land it is wise to take a look around to confirm the electronics are giving a believable fix. I well remember sailing in Greece when a Nato exercise was taking place. There was no navigational warning given, but each time a plane hove into view the handheld GPS advised us to change our course by 180 degrees! I wonder whether similar signal corruption is to be found in the firing ranges that make up half the south coast cruising area?

Rob.

sorry rob, no you don't need to plot the latest fix. My paper charts stay in the locker except for long, unknown passages. Even Tom Cunliffe says his paper charts are a mere backup.

 

[Elessar]

I still mark my position on a paper chart at intervals. If your electronics pack up, it would be useful to know your position within the last hour.

with 4 completely independent chart plotters on board, its a chance I can take. I log the lat long at intervals when offshore as a belt and braces, but don't bother with the chart.

 

[alahol2]

I've occasionally thought that an informal diary ("narrative log"?) would be nice to look back on, but I've never got round to actually writing one.

I've got 35 years worth above my desk at home and yes, when getting 'twitchy' during the winter, they can bring back some super memories (as well as all the embarrassing cockups).

 

[rob2]

Even Tom Cunliffe says his paper charts are a mere backup.

But that doesn't nrcessarily mean it's best practice! The discussion started talking about GPS navigation, but that doesn't mean a chart plotter on my boat. Even if you record the lat/long in the log without recording it on the chart, you should put your pinkie on the chart and then look around to see if you see what you should. Best practice demands that you use ALL aids available to cross check. Anyway, if you're sailing within sight of land that's usually the most interesting feature of the view.

Rob.

 

[Spirit of Glenans]

We always plotted position on the chart all the time. We always make log entries. I thought it was standard practise?

+1. I would have thought that the recommendation for those of us in the average age group taking part in these forums was to use all possible means to keep the mind active, so as to ward off senile dementia. Being spoonfed by an electronic plotter does not fit into this scenario. Although I have taken the time to read the manual and learn how to use it, my view is that the plotter is a back-up to the paper charts and logbook.

 

[prv]

+1. I would have thought that the recommendation for those of us in the average age group taking part in these forums was to use all possible means to keep the mind active, so as to ward off senile dementia. Being spoonfed by an electronic plotter does not fit into this scenario. Although I have taken the time to read the manual and learn how to use it, my view is that the plotter is a back-up to the paper charts and logbook.

If the only reason for keeping a logbook is to ward off dementia, I think I'll happily leave it for another thirty years

Pete

 

[ghostlymoron]

Even with four plotters, you are still vulnerable to power failure.

with 4 completely independent chart plotters on board, its a chance I can take. I log the lat long at intervals when offshore as a belt and braces, but don't bother with the chart.