jimbaerselman
Well-Known Member
And even with four plotters, plus power, you're vulnerable to GPS signal interference or degradation
The Old Ways of Navigation
- Thread starter yachtorion
- Start date
prv
Well-Known Member
Not when two of them have their own internal batteries
The same two also have multiple position sources, in that they receive GLONASS signals as well as GPS. Though I understand that electromagnetic interference to one of them is likely to affect the other as well.
Pete
yachtorion
Well-Known Member
My original point wasn't inteded as so much that GPS is unreliable as I was surprised that my single bearing based manual position had turned out to be substantially more accurate.... Makes me think I won't rely on GPS alone for pilotage. Not because the GPS might fail, but because the accuracy isn't guaranteed, and a simple double check is after all really easy!
prv
Well-Known Member
Sounds like a good lesson!
I certainly make use of a GPS plotter for pilotage these days, but never ever exclusively. All the places I sail are well marked and buoyed, and I will always be checking off the buoys, comparing the light characters at night, using bearings, etc. I don't usually make formal plans or deploy the full panoply of RYA pilotage techniques, but just driving the little boat across the little screen while not paying attention to the physical surroundings would just feel so, so wrong.
Pete
Hadenough
Well-Known Member
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.
Impressed with your reversion to manual means of navigation but don't rely on the accuracy of your hotel room fix too much! It's a bit different when you are in a pitching boat and cra**ing yourself! All for keeping a plot on paper for back up, electrical failure, the yanks switching off the satellites, whatever. Believe me, having lived through charts, RDF, Decca, la di da dida, there ain't nothing like GPS!
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yachtorion
Well-Known Member
I agree with everything you said. GPS is amazing. GPS double-checked with something else is even better!
srm
Well-Known Member
But what provides the position input? GPS? if so are they realy independent?
reeac
Well-Known Member
We have two fixed GPS - a Garmin and an MLR each with its own antenna. Their position read outs always agree within 2-4 metres when I've checked - we mainly use the MLR as it's connected to the Tacktick system.
knuterikt
Well-Known Member
Since both receivers sit on the same boat, they would be subject to the same interference..
So having all satnav equipment on board show same position is not that surprising, but they can still give wrong position because if interference.
I have several times observed that that my GPS plots me in the wrong position, if had been using GPS instead of AToN's I would have been sitting on a rock.
Some of these incidents have happened in places I sail regularly and these kind of error is not tied to location, most of the time my visual position and GPS is the same.
Minchsailor
Well-Known Member
About 15 years ago I was sailing from Alderney towards the Needles, approaching the IoW I heard a yacht putout a Mayday (although it ought to have been a Pan-Pan-Pan, as no danger of life was imminent).
They had lost their steering. Position they gave was in the vicinity of the east of the IoW. although they insisted they were about 2 1/2 hours out of Poole - which would have been good going for a sailing yacht. When questioned by the CG they were adamant. Visibility was excellent.
A bit later I sighted a yacht doing 'funny things' off the stbd bow. Went over to have a look and it was the yacht involved. Called up the CG, gave them the position - about 7 miles SW of the Needles LH.
Turned out their GPS repeater was misreading, and they had never bothered to look out of the window to check the position.
BTW they got the Yarmouth lifeboat out for a tow back. I gather the cable had come off the quadrant on the rudder stock (poor maintenance). This was a largeish Westerly and I know that model had a fitting for an emergency tiller to be fitted, which in the conditions would have got them home without the tow.
They had lost their steering. Position they gave was in the vicinity of the east of the IoW. although they insisted they were about 2 1/2 hours out of Poole - which would have been good going for a sailing yacht. When questioned by the CG they were adamant. Visibility was excellent.
A bit later I sighted a yacht doing 'funny things' off the stbd bow. Went over to have a look and it was the yacht involved. Called up the CG, gave them the position - about 7 miles SW of the Needles LH.
Turned out their GPS repeater was misreading, and they had never bothered to look out of the window to check the position.
BTW they got the Yarmouth lifeboat out for a tow back. I gather the cable had come off the quadrant on the rudder stock (poor maintenance). This was a largeish Westerly and I know that model had a fitting for an emergency tiller to be fitted, which in the conditions would have got them home without the tow.
Sorry, went a bit overboard there. What I really feel is that one of the joys of sailing is the fulfilment to be experienced by using all the skills and black arts acquired. I enjoy using paper charts andtaking fixes by the various means possible, when piloting in sight of land, and doing EPs when navigating on longer, offshore passages. The chartplotter is useful for confirmation/comparison, but relying solely on it would diminish the experience for me.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
oldsaltoz
Well-Known Member
Like others have stated, GPS is not 100% and anyone not checking their position by other means and recording may live to regret it. or not.
All my charts are laminated so marking them then wiping them clean avoids damage, and I like to record my findings regularly when not in open open.
I have witnessed boats coming to grief with GPS running but giving the correct information.
Based on almost 60 years of sailing, my advice would be trust nothing, check everything.
We have charts, GPS and Radar but still maintain regular chat checks.
Other hazards with GPS include vessels sailing in different directions to the same mark and not allowing sea room at the rounding. or sailing between the same two marks in opposite directions, again no sea room.
So, maintaining a perfect course can be complicated with no forward watch.
Finally, just to make things interesting, much of the existing charts for us in Oz are still unchanged from Cpt Cooks survey. So we really do need to keep an eye on depth and forward looking depth sounders are a blessing.
Bottom line, keep a record, keep a look out, and you may never have to buy another boat or deal with insurance people.
Good luck and fair winds.
All my charts are laminated so marking them then wiping them clean avoids damage, and I like to record my findings regularly when not in open open.
I have witnessed boats coming to grief with GPS running but giving the correct information.
Based on almost 60 years of sailing, my advice would be trust nothing, check everything.
We have charts, GPS and Radar but still maintain regular chat checks.
Other hazards with GPS include vessels sailing in different directions to the same mark and not allowing sea room at the rounding. or sailing between the same two marks in opposite directions, again no sea room.
So, maintaining a perfect course can be complicated with no forward watch.
Finally, just to make things interesting, much of the existing charts for us in Oz are still unchanged from Cpt Cooks survey. So we really do need to keep an eye on depth and forward looking depth sounders are a blessing.
Bottom line, keep a record, keep a look out, and you may never have to buy another boat or deal with insurance people.
Good luck and fair winds.
alahol2
Well-Known Member
I must admit I have never seen the GPS go ape whilst I've been sailing. What happens to the 'track' on the chartplotter when the GPS gets degraded for whatever reason. Does it suddenly jump to another location or does it gradually wander off course? Similarly what happens to speed over the ground, many people now say they don't use a log and are quite happy to use the SOG from the GPS. Wouldn't they notice something awry just by a look at the chartplotter?
I'm not advocating having no other means of navigating, just wondering if the predictions of doom are maybe just a tad overdone?
I'm not advocating having no other means of navigating, just wondering if the predictions of doom are maybe just a tad overdone?
johnalison
Well-Known Member
Although my GPS occasionally will lose its fix for a short time, usually a few seconds only, it has seldom let me down since I started using one sixteen years ago. There may be exceptions, but it looks to me as if the position is either correct, within the system's errors, or sufficiently wrong for the error to be obvious. The exception to this might be when GPS jamming is occurring, one reason why I will be leaving my charts in view when sailing.
Elessar
Well-Known Member
All completely independent. Different receivers. Different power supplies. Possibly the same satellites but so much redundancy there. Good enough for me.
BrianH
Well-Known Member
I bought my Trimble Ensign early in 1992, in Singapore, for not much under $1000
. Used in SE Asia, Adriatic and Ionian, I never experienced any hiccups, ever. It had relatively limited functionality (3-channel, satellite and coordinates display only). But then none of the areas I have used it in were influenced by military jamming, fairly common in northern Europe, which can wipe out the minute signals so very easily. But I still am aware that even with plotter, HH GPS receiver, AIS with integrated GPS - all independent from each other - a loss of signal in my locale will have me resorting to DR with my paper charts. But at least I will have a recorded position report no older than one hour.
Boreades
Well-Known Member
Am I imagining it, or has there's been a thread or two here in the past on NATO exercises, announced in advance, where GPS was going to be affected?
prv
Well-Known Member
ghostlymoron
Well-Known Member
Quite so. And is it really so much of a hardship to record your position every so often? I enjoy doing it - there's often not much else to do.
I bought my Trimble Ensign early in 1992, in Singapore, for not much under $1000
Elessar
Well-Known Member
Ha. a good reason to plot ones position at last.
Forget all this guff about modern plotters being unsafe, but if you enjoy plotting your position on a chart then that is a very good reason to do so, is it not?
And the record of the voyage with it's highs and lows so you can enjoy recounting it only really works on paper.
