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17-11-2017, 15:02
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#16
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Registered User
Join Date: Mar 2017
Location: Brisbane, Australia
Posts: 147
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Re: distance between two fix
Quote:
Originally Posted by NevisDog
It gets complicated when sailing west to east (or the other way?), eg when crossing from Oz to NZ - what time is chosen as "noon"? I believe the clipper ships running down the southern ocean would record 23 hour days as they could cover the distance between time zones in those high latitudes in a single day.
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No problem if one has a Navigation chronometer set on GMT -
In the days before electric string took the art and skill out of Navigation this was SOP, I still use a Sextant from time to time just to keep my hand in, although not many do nowadays, it has become too easy.
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17-11-2017, 15:10
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#17
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Registered User
Join Date: Mar 2015
Location: New Zealand
Boat: Moana 33
Posts: 1,092
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Re: distance between two fix
Clipper ships carried chronometers but they still worked noon-sight to noon-sight. I found using GMT was upsetting for watch changes, and very confusing when we reached port. Much prefer adjusting for local noon.
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17-11-2017, 15:13
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#18
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Registered User
Join Date: Feb 2013
Location: Kingston Ont Canada
Boat: Looking for my next boat!
Posts: 3,101
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Re: distance between two fix
Quote:
Originally Posted by conachair
Each midday, I write in the logbook the GPS total log distance and the water log total distance. Then days run is simply that minus yesterdays figures. And hopefully the GPS days run is more than the log wheel as you've some nice current with you
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I did the same when crossing the Atlantic. Noon every day I recorded the position in my log. Easy enough to calculate distance run from noon to noon. I would also send the position via sat phone txt/sms to my shore based support. That way my kids could also follow along on a big wall mounted chart....and if there was trouble they would know where to search.
So then you have to ask...when is noon? Not so easy, since when crossing an ocean you will likely cross a bunch of time zones...adding or subtracting an hour from a noon to noon run.
I think there must be an app that could help with this?
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17-11-2017, 15:50
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#19
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cruiser
Join Date: Nov 2017
Posts: 45
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Re: distance between two fix
Quote:
Originally Posted by henris
Hello,
On ocean crossings, skippers try to know the distance sailed in 24h. With the intention of writing an article on the various techniques (and tricks) used by sailors to determine this distance, I would like to know from our fellows blue water sailors how they do it. (Or if they do this daily routine).
Henri
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Have you ever heard of a dead reckoning..... course steered and (estimated) speed through the water.
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17-11-2017, 16:34
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#20
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Registered User
Join Date: Mar 2017
Location: Brisbane, Australia
Posts: 147
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Re: distance between two fix
Quote:
Originally Posted by NevisDog
Clipper ships carried chronometers but they still worked noon-sight to noon-sight. I found using GMT was upsetting for watch changes, and very confusing when we reached port. Much prefer adjusting for local noon.
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Noon sights are done at Mer Pass, thus giving a very simple sight reduction without tables to give an observed latitude.
Approximate time of Mer Pass is found by using the DR Longitude and the Almanac.
ie determining the time, usually GMT, when the LHA of the Sun is zero
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17-11-2017, 16:36
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#21
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Senior Cruiser
Join Date: Nov 2013
Location: Port Moresby,Papua New Guinea
Boat: FP Belize Maestro 43 and OPBs
Posts: 12,888
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Re: distance between two fix
Quote:
Originally Posted by hamburking
So then you have to ask...when is noon? Not so easy, since when crossing an ocean you will likely cross a bunch of time zones...adding or subtracting an hour from a noon to noon run.
I think there must be an app that could help with this?
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When is noon? When the sun is at its highest point in the sky.
When ocean crossing, it's optimal to record you location at local noon each day, regardless of what time zone you are currently working in. However, it is simpler to record it at noon for whatever time zone you are currently working in.
Lots of apps will tell you when local noon is for a given location.
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17-11-2017, 17:44
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#22
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Registered User
Join Date: Feb 2013
Location: Kingston Ont Canada
Boat: Looking for my next boat!
Posts: 3,101
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Re: distance between two fix
Quote:
Originally Posted by NevisDog
I found using GMT was upsetting for watch changes, and very confusing when we reached port.
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Quite right. You should try using UTC instead....
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17-11-2017, 18:56
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#23
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Registered User
Join Date: Mar 2015
Location: New Zealand
Boat: Moana 33
Posts: 1,092
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Re: distance between two fix
Quote:
Originally Posted by hamburking
Quite right. You should try using UTC instead....
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Hmmm... you sure that'll work better? How about zulu?
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17-11-2017, 19:41
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#24
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Registered User
Join Date: Jan 2015
Location: Punta Gorda, Florida
Boat: Lagoon450
Posts: 85
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Re: distance between two fix
Quote:
Originally Posted by henris
Hello,
On ocean crossings, skippers try to know the distance sailed in 24h. With the intention of writing an article on the various techniques (and tricks) used by sailors to determine this distance, I would like to know from our fellows blue water sailors how they do it. (Or if they do this daily routine).
Henri
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I may be the one off but I don’t care how many miles I sailed in 24 hours calculating fix to fix. What I do care about is how many miles I made good towards my destination. Not much math needed. For those that like to fix to fix calcs.....there is an app for that.
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17-11-2017, 19:50
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#25
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Moderator and Certifiable Refitter
Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: C.L.O.D.
Posts: 20,305
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Re: distance between two fix
Quote:
Originally Posted by woc
...... For those that like to fix to fix calcs.....there is an app for that.
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And the best app for this is found between the ears and aft of the forehead...
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
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17-11-2017, 22:33
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#26
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Registered User
Join Date: Apr 2016
Location: Indonesia
Boat: Outremer 55L
Posts: 3,804
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Re: distance between two fix
Quote:
Originally Posted by NevisDog
Hmmm... you sure that'll work better? How about zulu?
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Zulu is the old name for UTC, so the same time zone.
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17-11-2017, 23:12
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#27
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Registered User
Join Date: Mar 2015
Location: New Zealand
Boat: Moana 33
Posts: 1,092
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Re: distance between two fix
Quote:
Originally Posted by fxykty
Zulu is the old name for UTC, so the same time zone.
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18-11-2017, 00:40
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#28
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Registered User
Join Date: Mar 2014
Location: Sydney, Australia
Boat: Lightwave 38' Catamaran - now sold
Posts: 557
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Re: distance between two fix
Record the track on chartplotter and then note this at the end of the day or later, review (or download) and see how far you travelled. This is by far the easiest and most accurate option.
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18-11-2017, 01:36
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#29
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Moderator
Join Date: May 2008
Location: cruising SW Pacific
Boat: Jon Sayer 1-off 46 ft fract rig sloop strip plank in W Red Cedar
Posts: 21,155
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Re: distance between two fix
this is the commonest method:
Note the highest speed you see registered during the day. Assume that this was your average speed, so multiply the knotmeter reading by 24 to find your day's run. round the result up to the nearest even decade.
When you make landfall, repair to the nearest YC bar, and tell all who will listen that you have averaged this speed for your entire passage. If no one is impressed,come back the next day after rounding up another decade. Repeat as required.
Add in a couple of good gales (and perhaps a Tiger shark attack) and perhaps you will be respected in the manner you anticipated. Or perhaps not.
We've always just used the log readings for day's run calculations. Having a stout current helping you along gets you to the destination faster, but means little with respect to how well the boat (and the skipper) were doing.
Jim
__________________
Jim and Ann s/v Insatiable II, lying Port Cygnet Tasmania once again.
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18-11-2017, 02:41
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#30
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Senior Cruiser
Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 49,139
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Re: distance between two fix
Greetings and welcome aboard the CF, henris, and earlgray.
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"
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