mattonthesea
Well-known member
Today, crossing the German Bight shipping lanes!
When was the last time you used Dead Reckoning/Estimated Position or took bearings in anger?
- Thread starter LittleSister
- Start date
AndrewB
Well-known member
David Lewis commented that the training for a Polynesian navigator took 30 years! It required an amazing amount of detailed information and specialist understanding. I feel for the last generation to have gone through this training, 60 years ago, whose knowledge become instantly irrelevant with the introduction of the compass and sextant.
Perhaps the way some of us felt 30 years ago about the instant replacement by GPS of the navigation skills we had painfully acquired.
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dgadee
Well-known member
Don't you have OpenCPN and its great AIS handling?
I haven't used mine since the 1980s.
srm
Well-known member
AIS is an "aid to navigation", if your own observations are different to the AIS information use your own observations to avoid collision.
There are a range of reasons why the displayed AIS CPA/TCPA could be in error.
dgadee
Well-known member
A hand bearing compass is an "aid to navigaton" too. Just a different technology and probably harder to use with accuracy.
srm
Well-known member
Obviously.
The difference is that you have no knowledge regarding the set up or accuracy of another vessel's AIS transmissions and its inputs. However, you should be able to judge the reliability of your own observations.
One example of AIS error:
with a large vessel altering course your AIS will probably be calculating CPA using the movement of their GPS antenna, which is not a reliable indicator for CPA as it may be located astern of the ship's pivot point and turning in the opposite sense to their bow.
Having been involved in the education and training of MN deck officers we always emphasized the need to cross check and not rely on one source of information.
ColReg
"Rule 7 (c) Assumptions shall not be made on the basis of scanty information, especially scanty radar information".
This applies equally to AIS or any other "aid to navigation".
Birdseye
Well-known member
Last time I did a full day passage - its a way of passing time.
Ah - just seen the in anger bit. Got to be maybe 5 years or so, when my last Raymarine plotter went t*t* up. Had the lappy on board but chose to use paper charts and the old skills as much out of boredom as anything else.
Ah - just seen the in anger bit. Got to be maybe 5 years or so, when my last Raymarine plotter went t*t* up. Had the lappy on board but chose to use paper charts and the old skills as much out of boredom as anything else.
dgadee
Well-known member
True. But I learned to sail with hand bearing compasses and know just how difficult they are to use with accuracy. A tool. Just like AIS.
PS: and don't talk to me about RDF. Total waste of time. Today, navigation is just so simple even on a dark, windy night.
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AndrewB
Well-known member
Not totally bad, in the days when there were enough shore stations. I remember finding my old Seafix quite a blessing on the occasional dark windy night!
dgadee
Well-known member
OTE="AndrewB, post: 7980183, member: 176"]
Not totally bad, in the days when there were enough shore stations. I remember finding my old Seafix quite a blessing on the occasional dark windy night!
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I knew someone who went off in the opposite direction. He was very tired after dark and windy nights.
Not totally bad, in the days when there were enough shore stations. I remember finding my old Seafix quite a blessing on the occasional dark windy night!
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I knew someone who went off in the opposite direction. He was very tired after dark and windy nights.
john_morris_uk
Well-known member
I knew someone who went off in the opposite direction. He was very tired after dark and windy nights.
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User error rather than primitive technology being in error…. I think most of us have forgotten what it was like to sail 100 miles on DR and EP’s. If you were approaching a rocky coast in poor visibility any sort of position line was a welcome aid to your guesstimate of your position. I remember on more than one occasion being very relieved to spot the unmistakable sight of the very tall Vierge lighthouse appearing out of the mist and murkiness.
dgadee
Well-known member
User error rather than primitive technology being in error…. I think most of us have forgotten what it was like to sail 100 miles on DR and EP’s. If you were approaching a rocky coast in poor visibility any sort of position line was a welcome aid to your guesstimate of your position. I remember on more than one occasion being very relieved to spot the unmistakable sight of the very tall Vierge lighthouse appearing out of the mist and murkiness.
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Tiredness leads to all kinds of errors. RDF magnified his.
capnsensible
Well-known member
Tiredness leads to all kinds of errors. RDF magnified his.
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Actually, I got plenty of helpful position lines from RDF sailing back and forth across the English Channel pre GPS. Just a matter of practice really. Same with the brilliant hand bearing compass. Accurate in the hands of anyone who is prepared to use it a lot.
As mentioned up thread by a pro, multiple sources of information are way to go for me.
R.Ems
Active member
I wish RDF still existed, it sounds interesting to learn, and a useful back-up/corroboration of other methods.
And they have a built-in HBC. And use would improve your Morse.
The handheld gagets have a certain 1970's Dr Who charm as well. And you can get the Shipping Forecast on LW..
Ferrite rod aerials are still directional, I got the Shipping Forecast on LW from S.Utsire by carefully turning a transistor radio, which also gave me the benefit of an an approximate true bearing to Droitwich!
And they have a built-in HBC. And use would improve your Morse.
The handheld gagets have a certain 1970's Dr Who charm as well. And you can get the Shipping Forecast on LW..
Ferrite rod aerials are still directional, I got the Shipping Forecast on LW from S.Utsire by carefully turning a transistor radio, which also gave me the benefit of an an approximate true bearing to Droitwich!
capnsensible
Well-known member
Yeah, morse, around 12vletters iirc was part of the Yachtmaster (Offshore) assessment.
I totally get that modern electronics have improved safety and the ability for thousand more leisure sailors too put to sea....but even I get fed up with gazing at a screen sometimes.
Anyone remember that vhf signal that used to transmit off the western of the Isle of Wight somewhere? Counting the 'beats' gave you a bearing. Forget how it worked now......
R.Ems
Active member
That last one sounds like a VOR beacon intended for aviation; I'm a few decades out of date but I believe it's still part of the Private Pilot's licence syllabus, using technology which would have been familiar to Bomber Command in WW2..
srm
Well-known member
Sounds similar to Consol, somewhere in the LW band. Signal consisted of a series of dots that turned to dashes (or other way around). Counting them gave approx position lines good to +/- 20 miles if you had the chart. Only one station was still operating when I started using it but that was very helpful out in the North Sea if you could cross it with a RDF beacon.
I also used to carry a sextant, mainly for vertical angles to lights to obtain distance off during the day. That way you could get a reasonable fix from one mark with brg + distance off.
As I mentioned earlier in the thread navigation used to be an art and the intelligent combining of a number of techniques was required on most longish passage. It seem that I am not the only one who misses the challenges and satisfaction that have been taken from us by digital read outs and screens. Though any competent navigator should still be aware that the real world is all around them and the screen is a simplified representation that is still capable of misleading at times or of being miss read just like any other aid to navigation.
dgadee
Well-known member
The Rennaissanc and communication scholar, Walter Ong always said that the more expert you are on the past, the less likely you want to return there. You lot are the exception which proves the rule.
mattonthesea
Well-known member
On two occasions big ships' AIS indicated alternating turning directions. So I took bearings to confirm that collision was not imminent.
Then I hailed one!
srm
Well-known member
I have never understood this saying, please explain, exactly how can an exception prove a rule? Surely, if there is an exception it can not be a rule.
As to not wanting to return to the past, my boat has all the electronic toys and I also know how to use them correctly. As a result I also know their limitations and why they can be in error. I prefer to continue the basic philosophy of past navigators and cross check using independent means. However, I would not try to insist that you or anyone else follow this philosophy. Fortunately, we are all free to run our boats as we choose and many are happy in their belief that GPS and other digital outputs are infallible.