if GPS were not available

[Bilgediver]

What would your next best indispensible aid to navigation be?

Pencil !

 

[NorthUp]

I once suggested a large ball of string to a diver driving a RIB.

 

[john_morris_uk]

Before GPS we were always getting called up by yachts midocean - "havent seen the sun for days - can you tell us where we are please?". It was almost expected as soon as we saw a yacht on the horizon. I doubt many would own up to it though.

Suggest a VHF might be a useful tool - as well of all the other yokes.

CC

OK - I'll admit in public that I've had a chat to a ship and asked for my position. I also recall that I was chuffed that my DR was only a mile or two from where the ship said I was - and then felt a bit of a cheat. For the whole generations of sailors who have never not really known where they are, making a safe landfall - even across the channel - was a great feeling for the navigator.

Calling up a ship mid ocean used to be a pleasure - the officer on the bridge was usually glad of someone to chat to to relieve the boredom and we would chat about anything for a while.

I remember last using 'talk to a ship (and what position am I please?)' in the early days of Satellite Nav systems - transit satellite if I recall correctly. A few of us used to call it 'Chat-Nav' (instead of 'Sat Nav') when asked how we checked our position without a sight....

 

[Malabar]

Trinity House seem to be putting their money on e Loran. Lots of power; low frequency; better than 10m accuracy. USA is "watching with interest" and not completely removing the old Loran C infrastructure just yet.

 

[NormanS]

I have a friend who doesn't believe in all this modern new-fangled stuff like magnetic compasses, and paper charts. He works on the "See Water" principle. If he can see water, he just goes for it.

I Suppose it's a bit like that diet, the See Food diet.

 

[DaveS]

Low tech navigation

I read somewhere that the Polynesians could detect faint ocean swells by lowering their testicles into the sea.

Don't fancy that idea in Scotland.

 

[bluemerlin]

....and a book on astronav....

Astro-navigation from Square One to Ocean-master might do - 2011 version just published.

 

[Twister_Ken]

There's an apocryphal story about a yottie at sea, days without a sight, happening upon one of HM's survey ships. VHF - "wonder if you could oblige me with you position?"

"Certainly sir, would you prefer the position of our bow or our stern?"

 

[Signed Out]

There's an apocryphal story about a yottie at sea, days without a sight, happening upon one of HM's survey ships. VHF - "wonder if you could oblige me with you position?"

"Certainly sir, would you prefer the position of our bow or our stern?"

And please avoid running through our trailing sensors sir...

 

[jimi]

I recall a post by Mirelle, relating how when sailing in fog, they thought they were intering Dartmouth but upon landing it proved to be St Mary's

 

[Liz_I]

Loran C - It's still running as far as I know.
Hand bearing compass, Chart, Pencil, RDF set, Sounder..... all the good stuff!

I have become lazy with my navigation since GPS but I have resisted the chart plotter thus far. I still use paper charts every trip and plot the position hourly so I'm not as rusty as some.

+1

Long passages are boring so old fashioned chart work whiles away the time. It also gives you a head start if something goes wrong with the electrics. You know where you are. Modern stuff is great and long may it continue however total reliance without any other knowledge is a recipe for disaster should systems fail.

 

[VO5]

I'd be surprised if such a table existed (although I expect to be proved wrong now...). The problem is determining when you are looking at sunset/sunrise. It occurs when the centre of the sun is on the rational horizon, as you probably already know, and due to the effects of refraction the sun actually appears to be approx a semidiameter above the visible horizon at this time. If the sun was simply dropping vertically then the instant could be more or less pinpointed, but in any latitude outside the tropics the sun is dropping at an increasing angle to the horizon - to the degree that the actual instant of sunset / sunrise is somewhat difficult to pinpoint. Chuck in variables of refraction due to you low height of eye, and high latitudes and you have a bit of an impossible task.
The "equal altitudes" method described above is something I train young officers to do. Its an excellent tool to get some confidence with a sextant, and we've had position circles of approx 2 miles diameter if done properly. That is plenty accurate enough for mid-ocean.
CC

If I am allowed to return this discussion to serious interchange of ideas rather than the habitual exchanges of flippancy and the usual nonsense on these boards, I must comment you are perfectly correct sir.

In high latitudes the sun will slope as it sets and rises, and at the equator it drops vertically on setting and it rises vertically at sunrise.

I will further concede that a diminshed H of E will make sight taking more tricky in the higher latitudes.

When you mention "equal altitudes" you mean averaging for noon altitude estimation I presume ?

But the real question is whether differnces converted from arc to time (not for longitude but for parallels of latitude) actually have been worked out.
This begs the question as to whether tabulations for this calculation actually exist.

It has stimulated my curiosity since hidden in the mists of time there are calculations (like Lunars, for example) not in current mainstream use.

As the poster who follows very aptly points out, evidence from the ABC tables would suggest the differences to be so small as probably to be of very limited use and indeed accuracy.

But I am still curious as to whether any work has been done on this idea and if any properly accredited results exist.

 

[JayBee]

....But the real question is whether differnces converted from arc to time (not for longitude but for parallels of latitude) actually have been worked out.
This begs the question as to whether tabulations for this calculation actually exist.

I don't have a recent copy of the Nautical Almanac handy, but sunrise and sunset times were, and probably still are provided in the daily pages, for a range of latitudes on the Greenwich meridian between 72N and 60S.

The tables of True Amplitude in Burton's are entered with latitude and declination to get amplitudes in both arc and time. The tabulated time amplitude is unique to Burton's, I think. It is the difference between the rising and setting times and 0600, 1800. By adding the time amplitudes to 12 hours, it is straightforward to get the length of time the sun is above the horizon for combinations of latitude and declination. Hence knowing the sun's declination and the interval between sunrise and sunset it is possible to get a VERY rough idea of latitude. This gets progressively rougher around the equinoxes and at all dates in low latitudes.

 

[VO5]

I don't have a recent copy of the Nautical Almanac handy, but sunrise and sunset times were, and probably still are provided in the daily pages, for a range of latitudes on the Greenwich meridian between 72N and 60S.

The tables of True Amplitude in Burton's are entered with latitude and declination to get amplitudes in both arc and time. The tabulated time amplitude is unique to Burton's, I think. It is the difference between the rising and setting times and 0600, 1800. By adding the time amplitudes to 12 hours, it is straightforward to get the length of time the sun is above the horizon for combinations of latitude and declination. Hence knowing the sun's declination and the interval between sunrise and sunset it is possible to get a VERY rough idea of latitude. This gets progressively rougher around the equinoxes and at all dates in low latitudes.

Unfortunately at the moment I have neither to hand.
But from memory I am sure you are right with regard to the tabulation in The Nautical Almanac for Sunrise and Sunset times for different latitudes, though I think they may be at 10 degree intervals (so some interpolation will be necessary).
Using argumements Declination and Arc Time to obtain Latitude is a clever use of ABC I had not considered.
This is a very neat solution. Many thanks.

 

[Grumpybear]

I recall a post by Mirelle, relating how when sailing in fog, they thought they were intering Dartmouth but upon landing it proved to be St Mary's

Lots of cases like that from the days of sail. A French ship of the line, heading up channel for Le Havre, found herself in the Bristol Channel with a SW gale blowing. Her crew probably owed their survival to being promptly captured by the British.

And then there was the Torrey Canyon.....

 

[Searush]

Lots of cases like that from the days of sail. A French ship of the line, heading up channel for Le Havre, found herself in the Bristol Channel with a SW gale blowing. Her crew probably owed their survival to being promptly captured by the British.

And then there was the Torrey Canyon.....

And Sir Cloudsley Shovel who is famously alledged to have had a rating flogged for suggesting that he was headed into disaster, before running his own vessel & the entire following squadron on to the Scillies, If I Remember Correctly.

 

[jimi]

And Sir Cloudsley Shovel who is famously alledged to have had a rating flogged for suggesting that he was headed into disaster, before running his own vessel & the entire following squadron on to the Scillies, If I Remember Correctly.

Which, iirc, forced the admiralty to launch a competion for a timepiece capable of accurate time?

 

[Scotty_Tradewind]

I read somewhere that the Polynesians could detect faint ocean swells by lowering their testicles into the sea.

Don't fancy that idea in Scotland.

You may have been unfortunate to have missed a great talk by Tristan Gooley which included that and more at http://www.henleyoffshore.org/events.htm#next_event

Tristan is the founder of a natural navigation school, author of “The Natural Navigator” book and the only living person to have both flown and sailed solo across the Atlantic. He is a Fellow of both the Royal Institute of Navigation and the Royal Geographical Society and the Vice Chairman of Trailfinders.
See his website at www.naturalnavigator.com
A talk that starts with solo crossings of the Atlantic in a light aircraft and then a small yacht, before plunging into the very rare art of natural navigation.

Tristan describes how his love of the subject grew from realising that electronics were getting in the way of a good journey and explains how he learnt to find his way using the sun, moon, stars, weather and animals.

He describes the extraordinary techniques that have been used by the Pacific Islanders for centuries to find their way, the same methods that left Captain James Cook deeply impressed, and how natural awareness can enrich all nautical journeys to this day.

But on the 14th of March HOG have another treat in store.

Rodger Brydges
Rodger Brydges from the Marine Accident Investigation Branch will give a fascinating talk on “The Work of the MAIB”.
The Marine Accident Investigation Branch investigates accidents involving ships fishing boats and leisure craft on behalf of the UK government. Roger Brydges has sailed all his life and has worked for the MAIB for the past 14 years. During that time he has been personally involved in several investigations into sailing boat accidents, and some of these will be described in detail, together with the lessons learned.

Roger will also describe the wider context of the MAIB’s work including the increasing use of voyage data recorders (marine “black boxes”) which has revolutionised the way in which investigations are conducted.

All welcome, just £7 on the door for nonmembers.