Go Back   Cruiser Log World Cruising & Sailing Forums > Cruising Forums > General Cruising Forum
Cruiser Wiki

Join Cruiser Log Today

Reply
 
Thread Tools Search this Thread Display Modes
 
Old 02-11-2007, 12:22 PM   #15
Rear Admiral
 
Join Date: Feb 2006
Posts: 437
Default

Where are we?

We're all here because we're not all there!

Cheers!

Kirk
__________________

__________________
Gallivanters is offline   Reply With Quote
Old 02-11-2007, 12:45 PM   #16
Admiral
 
Trim50's Avatar
 
Join Date: Feb 2006
Home Port: Who cares really...
Vessel Name: T
Posts: 1,215
Send a message via Yahoo to Trim50
Default

No truer statement[V] Still counting the months and dollars...this part sucks!
__________________

__________________
[
Trim50 is offline   Reply With Quote
Old 02-11-2007, 01:32 PM   #17
Admiral
 
Nausikaa's Avatar
 
Join Date: Sep 2005
Posts: 1,619
Default

I qualified as a ship master before GPS was invented and so I love working with my sextant. It is a tremendous piece of kit that has been arround for a very long time. I also enjoy working out my sights using the Marc-St.Hillare method, i.e. logarithms and haversines rather than using the tables of computed azimuth and altitude.

Having said that, I think GPS is great. In the 'good old days' I remember Atlantic crossings where we saw no sun all the way. Approaching the Canadian coast was a nightmare because of Sable Island, low, engulfed in fog, poor radar echo and compared to today poor radars too. There was an RDF station but as the bearing was never particularly accurate and it was often just a degree or two on the bow it was not of great help. Sure there was LORAN, but how many European ships had that? DECCA worked fine closer to the coast but a the NE Canadian chain did not use the newer multi-pulse system one had to know one's position aaccurately to set it up.

Even the North Sea in foggy weather was a nightmare. Approaching the Thames from the North with all the sandbanks of England's east coast was a nightmare compounded by strong tides There are many examples of navigation made easier by GPS and I am all for it! Generally, it has also made it safer.

However, GPS is only an aid to navigation. It is not infallable and has to be checked against dead reckoning and other methods of fixing the ship.

One often hears, "what will happen if you lose power". My answer to that is how do you navigate with a sextant if you lose power. You need to know the time very accurately, with the exception of establishing latitude by meridian altitude. No idea at all to take stars without knowing the time. The moon you can forget too as it is so close its GP (geographical position) changes so rapidly that the exact time must be known. Morning and afternoon sun sights still require an accurate time if your position line wil not be out. So where do we get our accurate time signals from if the power is down? How many boats carry chronometers and of those how many navigators bother hemselves to rate the chronometes?

Let's move on folks. This is the 21st centuary and I am all for GPS used wisely. If you fall for the sextant back up argument, then be aware just how much kit you need. Sextant, rated chronometer(s), time signals, almanac, tables of computed altitude and azimuth (or equivilent Air Navigation Tables) or Norries Nautical Tables (or equivilent).

One final point on the sextant issue. Do I use my sextant? Yes. Where do I get the accurate time from? The GPS! And here is the interesting thing. Even if the GPS signals are out due to solar activity, the time signal will still be correct!

An on more point regarding navigation in general. I would say that most mistakes in navigation were made in plotting the position onto the chart. Irrespective if the position was obtained from sights, DF bearings, bearings and ranges, DECCA, LORAN, SINNS, CONSOL or OMEGA the actual plotting process was where misstakes crept in. The use of plotters or electronic charting removes that source of error. Sure, you should keep a plot on a paper chart but if you have a plotter or use digital charts on a computer then you can see immediately if your plot on the paper chart differs from the digital plot.

Aye

Stephen

Yacht NAUSIKAA
__________________
Yacht NAUSIKAA | Call Sign: 2AJH2




WHEN WAS THE LAST TIME YOU DID SOMETHING FOR THE FIRST TIME?

www.nausikaa.org.uk

= Sweden, Norway, Denmark, Lithuania
Nausikaa is offline   Reply With Quote
Old 02-11-2007, 02:32 PM   #18
Commander
 
Join Date: Aug 2004
Posts: 101
Send a message via MSN to dnelson
Default

Just to agree with JeanneP, Nausikaa, and others, I carry a second hand held GPS and insist on updating paper charts - and even keep a paper log with position, heading, and wind information (just in case.) As an electrical engineer you would think I would trust the electronics - But I don't.

In March 2003 I was crossing from the Galapagos to the Marquessas (a very lonely stretch of water) listening to the invasion of Iraq on the SSB and wondering if the US military would shut down the GPS system as a defensive measure. We had no sextant on board, no HO-249, and no Nautical almanac, but since it was march and we were so close to the equator we built a sextant (from a bit of board and a fishing weight) and figured if the worst happened we could work out a sun sight with a calculator and a clock.

Thankfully the GPS system never shut down (and we never really had to use our improvised sextant) but it could have become pretty harrowing had it been, and if we had nothing to fall back on...
dnelson is offline   Reply With Quote
Old 02-11-2007, 02:35 PM   #19
Admiral
 
Trim50's Avatar
 
Join Date: Feb 2006
Home Port: Who cares really...
Vessel Name: T
Posts: 1,215
Send a message via Yahoo to Trim50
Default

Aye Nausika!

Obviously you are a far wiser salt than I could ever hope to be and my minimal talents with my sextant are purely for entertainment and mental exercise while sailing. I am purely a beginner with it and still get a rush when I correctly find my GPS position. Even so, I still fully rely on the software to perform all the calculations. As such, I rely on my laptop and wireless GPS signal to provide the correct time. The only tools I need then are my sextant, laptop & software, battery and a reasonably fresh time signal. The chipset clock does a pretty darn good job of tracking time once given an accurate Zulu.

I would hope that newer generations of sailors will continue to keep the Old School methods alive in whatever technically aided form possible. Every time I stand on deck at twilight and try to align the sky with my star finder plot, Im always amazed by the fact that this was the norm of navigation for many centuries. Captains of old were some truly capable humans.
__________________
[
Trim50 is offline   Reply With Quote
Old 02-11-2007, 04:44 PM   #20
Admiral
 
Nausikaa's Avatar
 
Join Date: Sep 2005
Posts: 1,619
Default

Before Harrisson invented his chronometer the best navigators could do was establish latitude with accuracy. They used to sail to a predetirmined latitude and then cross the ocean at that latitude. Paralel sailing. After Harrisso came up with his invention mariners were able to establish longitude with some degree of accuracy.

When I was a cadet and junior officer we used to carry three chronometers and rate them daily against radio times signals. Why three? Because if one went south the other two, when corrected for chronometer error, would still be showing the same time. If we only carried two and one went south, how would we know which was wrong?

There is however a method of establishing longitude without using a chronometer. It is called lunar distances. Old Joshua Slocum was a master at lunar distances so when he wrote that he "boiled his clock" he was playing a bit of a joke on most of his readers who knew nothing about lunar distances. The method was very complicated, cumbersome and time consuming......but it worked. And as we know, Slocum didn't get lost (except once just out of the Staraits of Magellan but that had nothing to do with taking sights)Unfortunately, the tables needed to work out lunar distances dissapeared from nautical almanacs long ago.

I am impressed at Dave making a sextant. Not an easy task. Old navigators used what was caled a back-staff which, although far less accurate than a sextant, was easier to make. After the back-staff came the astralobe then the octant and finally the sextant as we know it.

Taking sights from the deck of a small boat isn't easy. In fact, taking sights from a large ship can be difficult at times. The ship / boat's motion and the lack of a good horizon create problems. Aur navigators solved the horizon problem by using a buble sextant. I believe that a German company even produced buble attachments for their marine sextants.

Another interesing thing is that when navigating in ice we had no real horizon so what we used to do was to fil a bowl with mercury and superimpose the true sun on the reflected sun in the mercury. The angle was then double the normal sextant altitude and so had to be halved but obviously did not need to be corrected for dip.

All this is intereting from an historical point of view and I too hope that the old methods are kept alive both for their own sake and as a back up if things go wrong but there is no point in ignoring new technology which in more case than not has made navigation easier, simpler and more accurate.

Having said that, the rush one gets after having taken a ship or boat accross an ocean using nothing but the sun and the stars and having the landfall turn up exactly as predicted has to be experienced to be believed. I still feel like shouting "eureeka" whan it happens - just don't ask me to run naked from the bath tub as old Archimedes did of yore.

Aye,

Stephen

Yacht NAUSIKAA
__________________
Yacht NAUSIKAA | Call Sign: 2AJH2




WHEN WAS THE LAST TIME YOU DID SOMETHING FOR THE FIRST TIME?

www.nausikaa.org.uk

= Sweden, Norway, Denmark, Lithuania
Nausikaa is offline   Reply With Quote
Old 02-21-2007, 03:17 AM   #21
Ensign
 
Join Date: May 2005
Posts: 7
Send a message via ICQ to bonezed
Default

fyi, there are now 3 GPS type systems.

Russian (GLONASS), European(Galileo), and American (GPS). Galileo will come online next year. Hopefully we'll see some receivers capable of using all 3 systems.
__________________
bonezed is offline   Reply With Quote
Old 03-01-2007, 12:34 PM   #22
Ensign
 
Bertje's Avatar
 
Join Date: Mar 2007
Posts: 1
Default

I know this tread is a bit old, but it is seemed to be a good first post as i now a few things about it...

At the moment the only satellite system that provides accurate positions is GPS. GLONASS is 'semi' operational, not all planned satellites are in orbit and some are broken. Receivers are hard to get (never seen one). Even Russian ships use GPS, GLONASS only has a advantage in very high lattitude due to the angle of the sat's orbits (so if you own a Nuclear Icebreaker and want to visit the north pole it might be wise to use it ). Galileo is not going to be operational for a few years as the sat's still have to be build, but the receivers should be GPS compatible.

Although asto navigation is still part of the STCW requirements and teached on nautical academy(?) the use of it on a yacht will not add much safety, you will need to practise it often to be able to produce a good position and I gues from a small and fast moving platform (like a yacht) its a lott harder than from the bridge of a 15000GT cargo vessel.

Apart from this: sextants are expensive kit and nautical almenacs aren't cheap either (and need replacement every year). So it might be wiser to invest this money (and the time) into something else that has a bigger added (safety-) value, like updated charts or better knowledge of the COLregs.

A last remark: if you see astro navigation as a hobby, its another story; the kick you get when you calculate a position without any electronics and are within 2 miles of the GPS is priceless

NB: i'm 2nd mate on oceangoing cargoships at the moment (with litle exp on small boats), but like to get a yacht and visit all those beautifull places I sailed past at 18kn the last years. This forum seems like a good start...
__________________
Bertje is offline   Reply With Quote
Old 03-01-2007, 12:56 PM   #23
imported_admin
Guest
 
Posts: n/a
Default

Welcome aboard Bertje. Thanks for the interesting information.

Enjoy your stay here.
__________________
  Reply With Quote
Old 03-01-2007, 01:46 PM   #24
Admiral
 
Nausikaa's Avatar
 
Join Date: Sep 2005
Posts: 1,619
Default

Indeed, welcome aboard. It is good to have another big ship sailor in the forum. I think we have a lot to offer this site, but a lot to learn too. This is a great forum where people willingly share their knowledge. Enjoy yourself here.

Aye

Stephen

Yacht NAUSIKAA
__________________
Yacht NAUSIKAA | Call Sign: 2AJH2




WHEN WAS THE LAST TIME YOU DID SOMETHING FOR THE FIRST TIME?

www.nausikaa.org.uk

= Sweden, Norway, Denmark, Lithuania
Nausikaa is offline   Reply With Quote
Old 07-15-2009, 10:57 AM   #25
Ensign
 
Join Date: Jul 2009
Posts: 12
Default

GPS is the primary means of navigation, and in the next few years we will see the whole area of GNSS expand with the addition of a revived GLONASS system (20 of the requisite 26 satellites currently operational, with another 6 going up later this year), as well as the European Galileo. In time we will see GNSS receivers that will use satellites from any and all of these systems together to provide a more reliable and accurate fix.

For coastal navigation, commercial vessels use radar as their secondary means of navigation.

Also, eLoran is slowly being rolled out in Europe (not sure what the status is in the USA), as Loran on steroids.

But using a sextant has a great feeling of achievement to it. If you want to avoid the need for almanacs and arithmetic, you could use a software package like WinAstro with it.
__________________
timtwickham is offline   Reply With Quote
Old 07-15-2009, 02:25 PM   #26
Commander
 
Join Date: Mar 2007
Posts: 130
Default

I would have to agree that there are too many sailors (sail and power) out there who have no idea of "where they are" and "where the closest safe harbor/landfall" is located. They just follow the chart plotter into oblivion or rocks sometimes. The real value of electronic navigation is "telling you where your are now." But a prudent navigator must write down or somehow remember this information AND it must agree with common sense/logic. If for some weird reason your GPS or plotter tells you that you have moved 150 nm from your last position in minutes or hours - there is something wrong and you need to find out what it is. Always having in your mind or on paper your basic route and ticking off your position now and then is essential. Also knowing what direction to point the boat should an emergency arise can save lives and money.

Most likely you will loose GPS positions because of power failure or GPS mechanical failure - I have had both even with relatively new GPS units. So be prepared to continue on using tried and true basic navigation techniques which really are not difficult or onerous to learn. Christopher Columbus made it across - without a sextant - using "constant latitude" sailing - keeping the sun angle above the horizon constant based on a "noon site" or something similar. Longitude had to wait for the invention of a good portable clock. Having a sextant in a life raft or even a boat requires either copious tables and an electronic calculator or just a dedicated navigation pocket calculator with an astro database. "Electronic" means it is also relying on batteries and subject to being wiped by solar flare or "EMP" effects just like a GPS.

Most sailing folks don't realize that 90% of all those airline flights from here to there around the world are using GPS as primary navigation. The US Air Force, nobody, is allowed to mess with the GPS system, turn it off, or anything - by Presidential decree and law or thousands of people could die from air crashes which would not be good for your re-election prospects. That does not mean that "natural events" - solar flares, etc. cannot take down or partially affect the GPS system, after all it was invented and managed by bureaucrats. So like old Chris Columbus, you had better know some basic navigation techniques.
__________________
osirissailing is offline   Reply With Quote
Old 07-17-2009, 01:01 PM   #27
Ensign
 
Join Date: Jul 2009
Posts: 4
Default

my 5 cents:

I know of very litle people who still do astro navigation, GPS has taken over. 2 GPS'es are cheaper than one good sextant.

but I do not agree with their arguments:

if you're sailing, then the argument of "the modern world we live in" makes no sense. In a modern world, people go by motorvessel and navigate electronically.

In the old fashioned world people go by wind force, and navigate with what the stars provide. For me, sailing is a way to keep old knowledge alive. If you were able and willing to learn to sail, then you should be able and willing to do astronavigation.

Of course you can have a manual GPS as backup, just like you have an engine to enter harbour.

Astro navigation is easy enough and is fun ! ( Just like using morse on the radio is ;-) )
__________________
- Work is for people who don't know how to sail -

JanB
JanB is offline   Reply With Quote
Old 07-17-2009, 01:07 PM   #28
Captain, Sailboat Reboot
 
Join Date: Nov 2007
Home Port: None
Vessel Name: Reboot
Posts: 110
Send a message via AIM to svReboot
Post

Quote:
Originally Posted by osirissailing View Post
Christopher Columbus made it across - without a sextant - using "constant latitude" sailing.
I understand from my reading that this method resulted in many near blind helmsman as they looked through a stick to keep the sun at the correct angle without the benefit of modern filters!
__________________

__________________
Roger
Current position http://www.winlink.org/dotnet/maps/Positio...?callsign=W2ZDB
Ham: W2ZDB Reboot: WDB8435
Web Site: http://www.sailboatreboot.com
Blog:http://blog.sailboatreboot.com
svReboot is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

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


Our Communities

Our communities encompass many different hobbies and interests, but each one is built on friendly, intelligent membership.

» More about our Communities

Automotive Communities

Our Automotive communities encompass many different makes and models. From U.S. domestics to European Saloons.

» More about our Automotive Communities

RV & Travel Trailer Communities

Our RV & Travel Trailer sites encompasses virtually all types of Recreational Vehicles, from brand-specific to general RV communities.

» More about our RV Communities

Marine Communities

Our Marine websites focus on Cruising and Sailing Vessels, including forums and the largest cruising Wiki project on the web today.

» More about our Marine Communities


All times are GMT. The time now is 05:19 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2016, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.0