Dead reckoning?

[olavs]

Friends

The term "dead reckoning" are frequently used in PBO articles. Could anyone please explain to a scandinavian what this navigation term means?

Thanks

olavs

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[AndrewB]

Navigating without GPS, from regular observations of the boat's speed and direction, and allowing for currents and leeway.

The term appeared in English about 400 years ago (OED: 1613), 'dead' meaning exact, as in "dead heat" (not as a corrupt form of 'deduced').

 

[muchy_]

It means if you keep on reakoning on it sooner or later you will be dead.

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[DanTribe]

Hi
I've always understood it to be a corrupted form of Deduced Reckoning. Meaning to calculate where you are, knowing where you started from, distance travelled and speed and direction of current etc.
Dan

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[Chris_Rayner]

AKA By guess and by God nm

.

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[Reap]

This is incorrect Andrew B
Dead reckoning is worked out from two sources only: Course steered and distance run from last known position.
A DR is the beginning of an EP (Estimated position) but leaves out Tide and Leeway and therefore is not at all accurate.
Therefore it is not 'exact' and therefore not in your words 'Dead'
Whilst I have no idea where the term came from I would tend to think that Deduced reckoning would be the more likely.

An EP is much more accurate and is the only way you will have any chance of getting close to your actual position.

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[Guest]

No thats EP - DR is :

Dead Reckoning is the calculation of position by course and speed from a starting point without correction for current / drift / leeway etc.

<hr width=100% size=1>Nigel ...
Bilge Keelers get up further ! I only came - cos they said there was FREE Guinness !

 

[ponapay]

According to that bible of

nautical navigation - The Admiralty Manual of Navigation (Vol 1)

Dead reckoning is the expression used to describe that position obtained from the TRUE COURSE STEERED by the ship and her SPEED THROUGH THE WATER, and from NO OTHER FACTORS.

It also says that "In practice the term dead reckoning is occasionally used to describe the EP. Such practice is incorrect and should be avoided"



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[LadyInBed]

olavs
marinewaypoints site has a <A target="_blank" HREF=http://www.marinewaypoints.com/learn/glossary/glossary.shtml#d>nautical glossary </A> which will be of help to you.

Dead Reckoning - The process of plotting a theoretical position or future position based on advancing from a known position using speed, time, and course, without aid of objects on land, of sights, etc. Term comes from deduced reckoning, abbreviated first to "ded reckoning".

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[ianwright]

Don't worry about it. Since the advent of electronic navigation systems the gene controlling the cluster of brain cells that had the ability to navigate by pencil has been turned off.
There are people sailing today who have never navigated by the application of pencil to paper,do not belivce such a thing is possable and so see no reason to try.

IanW

<hr width=100% size=1>Vertue 203, Patience

 

[Guest]

The Lord is my Shepherd and

I shall have battery's ........

I apologise to all those for my irreligious statement, but I think you know what I mean !!!!

It's nice to know someone cares about the old ways and that some can actually do it ......... despite many claims - it is still quick, easy and can be useful ---- especially if you learn to do an EP ....

<hr width=100% size=1>Nigel ...
Bilge Keelers get up further ! I only came - cos they said there was FREE Guinness !

 

[LadyInBed]

What do you do if your GPS packs up . . .

. . . plug your backup unit in and turn it on !!!

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[ianwright]

Re: What do you do if your GPS packs up . . .

I bought six backup units this week,,,,,,,,,,,Derwent Graphics 2B, 70 pence each.
Mind you,my Garmin and Yeoman Pro do make life simpler,,,,,,,,,,
.
It's the chap with £10,000 worth of electronics inc on board PC and 1500 pirated electronic charts who has no paper charts at all and no idea how to navigate who concerns me. He is off to the West Indies next spring! Come to think of it he knows nothing about climate either,,,,,,,,,,,,,

IanW.

<hr width=100% size=1>Vertue 203, Patience<P ID="edit"><FONT SIZE=-1>Edited by ianwright on 27/08/2003 23:13 (server time).</FONT></P>

 

[LadyInBed]

Re: What do you do if your GPS packs up . . .

. . . but I've got a National Geographic Atlas!

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[AndrewB]

Err ... 50-50?

You are right, strictly one ought to accept the Admiralty definition of DR, though the Shorter Oxford English Dictionary (1973 ed) gives: "the estimation of the ship's position from the distance run by the log and the courses steered by the compass, with corrections for current, leeway, but without astronomical observations". (My italics).

'Deduced' is however just folk etymology, which itself dates back to at least the 1950's. There is no evidence of any form prior to 'dead reckoning'.

 

[Reap]

Re: Err ... 50-50?

Indeed...though if I were to base my navigation on any one authority it would probably be the admiralty before Oxford dictionaries /forums/images/icons/wink.gif

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[MainlySteam]

Re: Err ... 50-50?

Bowditch, Pub No 9 (the American view), concurs with the Admiralty so I think we can safely assume they together overtake any other view.

However, I always thought that dead reckoning came from the fact that unless you got it dead right you might end up dead (just my vivid imagination at work)/forums/images/icons/crazy.gif

John

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[AndrewB]

But Dixon Kemp ...

... the British arch-authority on yachting in the C19th, gives in the final edition of the Manual of Yacht and Boat Sailing (1913):

Dead Reckoning.-- The calculation of a ship's position by the log, the courses she has made, lee way, set of currents, &c without an observation.

Other C19th and early C20th yachting writers I've checked also seem to prefer this definition.

Reap says he would always accept the Admiralty version over the dictionary. However, its worth remembering that the OED normally gives what is the accepted usage of a term, whereas the Manual of Seamanship makes clear that its definition is what the Admiralty considers proper, and so by implication not necessarily the common usage among seamen.

I, like you, would naturally accept the Admiralty version, which has been incorporated in RYA training. I wonder if they were actually trying to regularise the definition in the Manual of Seamanship (first published around 1915?), perhaps for training purposes. It's not too suprising that the current Bowditch is in accord, as there has been close co-ordination between US and UK authorities on navigation in the post-war era, but it would be interesting to see an older edition.

So ... we can agree on what the definition is now, but it seems historically it may have been more inclusive.

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[Reap]

You mis-quote me sir!

<blockquote><font size=1>In reply to:</font><hr>

Reap says he would always accept the Admiralty version over the dictionary.

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Now I think you will find what I actually said was:

<blockquote><font size=1>In reply to:</font><hr>

though if I were to base my navigation on any one authority it would probably be the admiralty before Oxford dictionaries

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I think you will find there is a subtle difference /forums/images/icons/laugh.gif

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[Guest]

OI ! Watch it !!!!!! about....

pirate charts !!!!

Anyone who undertakes any voyage out of sight of land / closed waters without knowing any fundamentals is just plain absolutely stone cold STUPID !!!!!


<hr width=100% size=1>Nigel ...
Bilge Keelers get up further ! I only came - cos they said there was FREE Guinness !