Cruisers Forum
 


Join CruisersForum Today

View Poll Results: If I had absolutely no GPS/Loran/Radar Etc. aboard I would...
call the coast guard 2 1.14%
uncomfortably switch to DR and be very nervous for the rest of the trip 20 11.43%
comfortably switch to DR but not mess with the celestial stuff 83 47.43%
break out the old sextent and go back to the way we used to do things 70 40.00%
Voters: 175. You may not vote on this poll

Reply
 
Thread Tools Rate Thread Display Modes
Old 20-04-2007, 01:56   #46
Moderator Emeritus
 
GordMay's Avatar

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 31,580
Images: 240
I can’t imagine using celestial navigation on most inland waters, except for practice.

US SAILING's Celestial Navigation Certification Standards only require a 5 mile accuracy, which I can reliably surpass with dead reckoning:
Celestial Navigation Certification Standards

Of course, you could use an altimeter (/w local pressure and temperature info’), or a 3D-fix on your GPS.

Great Lakes water levels are officially measured from the International Great Lakes Datum 1985 (IGLD 1985). This datum is referenced to sea level, as measured at Rimouski, Quebec, near the mouth of the St. Lawrence River.

Goto:

Great Lakes Information Network:
Great Lakes-St. Lawrence Levels and Hydrology

and

Current Great Lakes-St. Lawrence Water Levels:
Current Great Lakes-St. Lawrence Water Levels
__________________

__________________
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?"



GordMay is offline   Reply With Quote
Old 05-06-2007, 14:12   #47
Registered User

Join Date: Jun 2007
Location: San Diego
Boat: Gaff rigged sloop, 24'
Posts: 30
Celestial Navigation

Celestial Navigation is like riding a bicycle; it looks intimidating, but once you know how, it is easy. Most people say that they don't need it because they stay coastal, but when you leave the harbour and the mast breaks, there's no telling where you will end up. Other people will tell you that if they turn to port (or stbd) then they will find that big continent. If you are approaching land and you don't know how far off you are then you are lost.
__________________

__________________
NavPak ECS is offline   Reply With Quote
Old 06-06-2007, 18:41   #48
Moderator Emeritus
 
Ex-Calif's Avatar

Cruisers Forum Supporter

Join Date: May 2007
Location: Singapore
Boat: Maxi 77 - Relax Lah!
Posts: 11,514
Images: 4
"If I had absolutely no GPS/Loran/Radar Etc. aboard I would... "

Interesting poll. One question? Are we underway or at the dock. If I was at the dock I'd wanna know if there is any ice left in the cooler. Gotta know if this is an emergency or not.
__________________
Relax Lah! is For Sale <--- Click
Click--> Custom CF Google Search or CF Rules
You're gonna need a bigger boat... - Martin Brody
Ex-Calif is offline   Reply With Quote
Old 06-06-2007, 20:00   #49
Registered User

Join Date: Jun 2007
Location: currently on my boat in Mexico
Boat: 32 ft Ketch, Colin Archer type, Misty
Posts: 17
" One question? Are we underway or at the dock. "

What? This is a navigation poll. navigation implies fixing your position and that implies out of sight of land.
jenia
__________________
Jenia is offline   Reply With Quote
Old 06-06-2007, 20:14   #50
Registered User

Join Date: May 2003
Location: East Coast & Other Forums!
Posts: 913
The "right" answer for me does not appear.
Buy enough cheap GPS's and batteries so that you never need be concerned about one or more not working properly short of thermonuclear war. Cheaper and easier than using a sextant and a hell of a lot more reliable day and night and in all kinds of weather.
Flame away guys but I stopped hitching a horse to my car bumper some years ago too. (GRIN)
__________________
camaraderie is offline   Reply With Quote
Old 07-06-2007, 04:12   #51
Moderator Emeritus
 
Ex-Calif's Avatar

Cruisers Forum Supporter

Join Date: May 2007
Location: Singapore
Boat: Maxi 77 - Relax Lah!
Posts: 11,514
Images: 4
"What? This is a navigation poll. navigation implies fixing your position and that implies out of sight of land."

I guess I could use an education. How do I get a fix using Ded Reckoning?

PS - I am with Cameraderie. Learning celestial navigation is an interesting mental exercise but practicality is multiple GPSs. If the satellite network goes down you take the current charts, last known postion and aim for a big landfall...
__________________
Relax Lah! is For Sale <--- Click
Click--> Custom CF Google Search or CF Rules
You're gonna need a bigger boat... - Martin Brody
Ex-Calif is offline   Reply With Quote
Old 07-06-2007, 06:20   #52
Senior Cruiser

Cruisers Forum Supporter

Join Date: Nov 2005
Location: Out there doin' it
Boat: 47' Olympic Adventure
Posts: 2,635
Quote:
Originally Posted by Ex-Calif
"How do I get a fix using Ded Reckoning?

...you take the current charts, last known postion and aim for a big landfall...
I think you just answered your own question.
__________________
Lodesman is offline   Reply With Quote
Old 07-06-2007, 07:47   #53
Registered User
 
Amgine's Avatar

Join Date: Dec 2004
Location: Vancouver BC
Posts: 1,384
Images: 1
Not quite a fix...

The deduced (ded) reckoning will not provide a fix, but rather a good estimated position. If you can accurately determine speed, leeway, drift or set, course, and time this estimated position is quite reliable. But the longer you are from a true fix, the further you are likely to be from your estimate due to the accumulation of small errors.

Amgine

(To get the fix with ded reckoning, find the nearest safe landfall. Or have a sextant or other means of astronomical position fix.)
__________________
Amgine
Blog

On the internet, nobody knows you're a dog anchored in a coral atoll.
Amgine is offline   Reply With Quote
Old 07-06-2007, 19:24   #54
Moderator Emeritus
 
Ex-Calif's Avatar

Cruisers Forum Supporter

Join Date: May 2007
Location: Singapore
Boat: Maxi 77 - Relax Lah!
Posts: 11,514
Images: 4
"I think you just answered your own question."

I don't think so because when using DR after your last known fix you are lost. The magnitude of how lost depends on the currents, time and speed. You could be 800 meters lost or 800 miles lost.

"The deduced (ded) reckoning will not provide a fix, but rather a good estimated position."

That's exactly my point I guess. A fix is a fix and you can't get one by DR. You can know your last fix and you can estimate (deduce) where you've gone but without at least two landmarks (in sight of land), a star shot or a gps you don't know where you are and the circle described in a previous post just starts to grow.

Sorry to get so literal about this my previous post was meant to be a joke. Probably a bad one at that.

I guess it's important to be accurate in case anyone lurking without navigation skills gets the wrong idea.

Ded Reckoning - Time, drift and speed since a last known fix.

A Fix - A position on a chart confirmed by two (or more) bearings from known landmarks or a position calculated using celestial navigation or a gps lat & lon.
__________________
Relax Lah! is For Sale <--- Click
Click--> Custom CF Google Search or CF Rules
You're gonna need a bigger boat... - Martin Brody
Ex-Calif is offline   Reply With Quote
Old 07-06-2007, 21:13   #55
Senior Cruiser

Cruisers Forum Supporter

Join Date: Nov 2005
Location: Out there doin' it
Boat: 47' Olympic Adventure
Posts: 2,635
Quote:
Originally Posted by Ex-Calif
"I think you just answered your own question."

I don't think so because when using DR after your last known fix you are lost. ..."The deduced (ded) reckoning will not provide a fix, but rather a good estimated position."

That's exactly my point I guess. A fix is a fix and you can't get one by DR. You can know your last fix and you can estimate (deduce) where you've gone but without at least two landmarks (in sight of land), a star shot or a gps you don't know where you are and the circle described in a previous post just starts to grow.
...I guess it's important to be accurate in case anyone lurking without navigation skills gets the wrong idea.

Ded Reckoning - Time, drift and speed since a last known fix.

A Fix - A position on a chart confirmed by two (or more) bearings from known landmarks or a position calculated using celestial navigation or a gps lat & lon.
Well Amgine got it ("To get the fix with ded reckoning, find the nearest safe landfall"). Now to be very technical, a lot of fixing methods require a DR - visual and radar fixing can't be done unless you have a reasonable idea what your fixing points are; celestial with the intercept (or Marcq St Hilaire) method requires a starting point (assumed position); and even GPS - if your GPS didn't run its own DR, it would be forever in start-up mode and fixes would take minutes, rather than fractions of a second.
So we don't confuse anyone lurking without navigation skills, I'll correct your definitions: Dead reckoning - time, speed and course since last known position;
Estimated position - an improvement on the DR, as set is calculated so as to provide course and speed made good; and
Fix - is a position derived by measurement from reference points; when it is plotted on a chart, it is ancient history - in the time it takes for you to plot your lat and lon, lines of bearing, ranges etc, you have travelled away from that position and are on your DR. You are not "lost" when you are dead reckoning. If you are conscientious about maintaining it, you will find it surprisingly accurate. In the days before GPS (not that long ago) ships managed to find their ways across the oceans, thanks to DR.

Kevin
__________________
Lodesman is offline   Reply With Quote
Old 07-06-2007, 23:30   #56
Moderator Emeritus
 
Ex-Calif's Avatar

Cruisers Forum Supporter

Join Date: May 2007
Location: Singapore
Boat: Maxi 77 - Relax Lah!
Posts: 11,514
Images: 4
"So we don't confuse anyone lurking without navigation skills, I'll correct your definitions: Dead reckoning - time, speed and course since last known position;"

Actually Ded reckoning can be reduced to distance covered and direction. Distance covered is usually plotted as Speed * Time.

Course: Is the intended path over water or land. This is the line you plot on the chart.

Track is the actual path taken. Sometimes called course over ground or course made good.

It is relevant that both speed and track are influenced by current and wind. Speed over the earth will be different than speed through the water due to the influence of current and wind.

I don't disagree with anything you are saying actually and I use the word "lost" in a very figurative sense. The only time you know where you are with precision is when you have a good fix.

BTW - This is an interesting discusison thanks for your patience. But to remain in context I was only replying to this statement -

"What? This is a navigation poll. navigation implies fixing your position and that implies out of sight of land."

Navigation does not alway imply fixing your postion and in the context of the poll by asking to choose between Ded Reckoning, GPS and Celestial Navigation is specifically "excluding" position fixing in one of its answers. in particular we agree that you cannot get a position fix using DR when out of sight of land. The best you get is an estimation of your position calculated as best as possible using distance travelled and direction which is heavily influenced by the factors considered in the DR calculation.
__________________
Relax Lah! is For Sale <--- Click
Click--> Custom CF Google Search or CF Rules
You're gonna need a bigger boat... - Martin Brody
Ex-Calif is offline   Reply With Quote
Old 08-06-2007, 08:49   #57
֍֎֍֎֍֎֍֎֍֎

Cruisers Forum Supporter

Join Date: Apr 2006
Posts: 13,042
"I don't think so because when using DR after your last known fix you are lost. "
Nah. Lost means LOST as in, I was docked yesterday at the club and when I woke up today, the boat was surrounded by fog and sea with no power to anything. That's LOST.

When all you have got is your last DR position estimate and a vague idea of how long ago that was, you are still not LOST. Rather, the circle of uncertainty is just a bit larger than you might prefer.

Whether you've got DR, or fixes, or a GPS showing you where you MIGHT be located...all that counts is the circle of uncertainty, and the size of that circle.

Need to get through an inlet in the fog? Then the circle has to be pretty tight. Just need to "go west" in midocean? OK, then the circle can be rather large--and still not be a problem.

As Daniel Boone supposedly said, "I have often been surrounded by lostness, but I have never been lost." And he never had GPS!
__________________
hellosailor is offline   Reply With Quote
Old 08-06-2007, 17:57   #58
Registered User
 
Dreaming Yachtsman's Avatar

Join Date: Nov 2005
Location: Kennewick, WA
Posts: 490
Images: 5
Send a message via Skype™ to Dreaming Yachtsman
I voted to "comfortably switch to DR but not mess with the celestial stuff."

To all you qualified navigators and wannabe navigators, a word of caution based on a year of cruising the West Coast of Mexico and the Sea of Cortez: Do NOT put all your eggs in one basket (i.e. trust any ONE position source to the exclusion of all others).

Several times we sailed toward a port using our GPS/chart plotter only to find that the plotter showed us to be up to 2.5 miles east of where we actually were in relation to land. Several times it showed us on land when we were actually in the middle of a bay. This is not because of any shortcomings with GPS but rather because many charts of Mexico are based on surveys from the 1800's when navigation was not nearly as precise as it is now. Of course land masses on today's chart plotters reflect what the paper charts show.

One tool not listed in the poll that I find very useful when entering a port for the first time is radar. Often it is easier to fix your position by laying out range arcs than bearing lines, especially when navigation marks are difficult to identify (only a few mountains have distinguishing enough features to be reliably identified from sea).

I must confess that GPS has allowed me to become quite cavalier about navigation. Most of the time when not entering port I rely almost exclusively on the chart plotter. I have a hand held battery powered GPS and paper charts on board should a disaster strike the chart plotter. If the entire GPS constellation goes down, we will probably have bigger things to worry about than where our boat is.
__________________
John
Formerly S/V Yachtsman's Dream
Go sailing now. Life is too short not to enjoy it.
Dreaming Yachtsman is offline   Reply With Quote
Old 08-06-2007, 20:05   #59
Senior Cruiser

Cruisers Forum Supporter

Join Date: Nov 2005
Location: Out there doin' it
Boat: 47' Olympic Adventure
Posts: 2,635
That's a very good point about the radar, John. Have successfully used a radar station plotter (a chart-sized sheet of acetate with a manoeuvring circle on it) to plot fixes nearly 100 miles off-shore. Helps if there are distinct peaks, and you can't forget to convert radar miles to naut. miles. Not overly accurate mind you, but give or take a mile that far from land is pretty darn good.

Kevin
__________________
Lodesman is offline   Reply With Quote
Old 10-06-2007, 23:26   #60
Moderator Emeritus
 
Ex-Calif's Avatar

Cruisers Forum Supporter

Join Date: May 2007
Location: Singapore
Boat: Maxi 77 - Relax Lah!
Posts: 11,514
Images: 4
Excellent discussion. The point about the charts vs. gps positoin is excellent. Of Course if you obtain a fix with any method other than land based features you will have the same problem assuming the same chart.

As the little kid in the store yelled at the security guard, "Of course I'm not lost. I'm right here. Mommy is lost!"

I'm not lost I'm in the boat. Tahiti is lost...
__________________

__________________
Relax Lah! is For Sale <--- Click
Click--> Custom CF Google Search or CF Rules
You're gonna need a bigger boat... - Martin Brody
Ex-Calif is offline   Reply With Quote
Reply

Tags
navigation, poll

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Celestial Navigation Help Needed Loose Ends Navigation 67 10-11-2011 13:19
Free navigation software JanPeter Navigation 33 17-04-2009 18:05
Celestial Navigation SkiprJohn Navigation 45 29-12-2008 23:15
Magazine poll Pura Vida Forum Tech Support & Site Help 23 23-04-2007 15:51
Another Free Anchorage Gone - How Do we Fight This?? markpj23 General Sailing Forum 145 01-10-2006 20:47



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 00:13.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.