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05 May - Warmer weather, painting and navigating

RRS Ernest Shackleton Diary


Position at 1200 (UTC - 3 hours): 17° 28'5 South 038° 07'7 West
Next destination: Grimsby, Lincolnshire, England
ETA: Wednesday, 22nd May 2002
Distance to go: 4617.0 nm
Total Distance Sailed this Season: 26344.3 nm

Current weather: Bright and Sunny. Few clouds. Hot.
Wind: Northerly, Force 4-5
Barometric pressure: 1016.9 mb and steady
Sea state: Negligible swell
Air temperature: 28.5°C.
Sea temperature: 27.3°C.


Current, frequent weather observations reported back to BAS Headquarters in Cambridge is used to plot the ship's current position and recent track. Meteorological data are also available from this page. The callsign of RRS Ernest Shackleton is ZDLS1.


FID's ON RRS ERNEST SHACKLETON BEGIN ROTHERA REBUILD !

Working on the deck - Click to enlarge Working on the deck - Click to enlarge


The weather is hot and clammy and the forecast is for more of the same. So why was Richard the Casson and an entourage of out-of-work FID's working so hard on the helideck ?? It is suggested that the next season may get off to a late start due to 2nd year ice conditions precluding an early entry to the southern Antarctic stations, but is it not a little premature to be starting the Bonner Lab Rebuild whilst heading North - the completely wrong direction for Rothera ?? But there's no keeping a good Antarctic Team down, and the new Bonner Lab - although a little on the small side - looks as though it will be a sturdy structure and so low-profile as to avoid the worst of the Antarctic winds !!

For a full report on the final structure, - don't miss next weeks exciting episode of 'What will Richard Casson build next?' !! I understand NASA are looking for new designs for extensions to the International Space Station. Richard ??!!!.


BUT SERIOUSLY FOLKS !

Although it has been a week continually at sea for RRS Ernest Shackleton, it has not been uneventful. This is the time (and the weather) that we have all been waiting for. Notwithstanding Richard and his wooden liferaft construction, all the FID's have been gainfully employed onboard. We are travelling with a complement of 14 including Penny the Dentist and Jenny the Doctor. Penny has been busy 'dentisting' and Jenny has been busy 'doctoring'. They have been taking it turns in the infirmary to do doctors' surgery in the morning and dentist shop of horrors in the afternoon. God forbid if you got your appointments mixed up ??? 'But doctor, I only came in for an extraction - not an amputation !'.

The main influence on the week's activities has been our old friend the weather. It has to be said that RRS Ernest Shackleton is definitely a weather ship. 'Whether we stay around Bird Island, or whether we go elsewhere' ?? That just about sums it up. However, with the advent of the sun making an appearance, the shorts have equally been very much in evidence! As we left Stanley last weekend, there was a strong and freshening sou'westerly wind building up, but we escaped a hard time on board as the track of the ship took us nor'northeast and she rode the swells very well indeed. So seasickness has not been a issue on this voyage so far. By late Sunday afternoon we had changed our track to intercept the northerly Falklands currents that would speed us on our way along the coast of South America, and that took us towards warmer waters and bluer skies.

Blue Skies and Warm Temperatures.

Day

Sea Temperature °C

Air Temperature °C

Sunday

12.2

09.0

Monday

12.6

12.1

Tuesday

13.3

15.6

Wednesday

19.1

21.2

Thursday

24.2

24.2

Friday

26.3

27.3

Saturday

28.1

25.5



Here are the temperatures for the last 7 days and the rise is dramatic as can be seen, but not as dramatic as the temperature rise on the bridge where 360 degree windows allow streaming sunshine to enter all the daylight hours! The Engine room on the other hand manages to maintain a constant temperature all the year round.

CORRECTION. I have been corrected by the resident Engine Room Temperature Expert, Rob 'My Birthday Today' Mathieson who advises that the temperatures in the Engine room change accordingly. Apparently down in the Antarctic, temperatures can reach as low as 14 or 15 degrees whereas in the tropics, the temperatures soar to mid 30's ! Or in laymen terms, - going from wearing a t-shirt under the boiler suit to NOT wearing any shirts under the boiler suit - and still being hot ! I stand corrected Rob.


EAT YOUR HEART OUT MICHAEL ANGELO.

The biggest pastime onboard the ship this week has been the painting program. From about Tuesday onwards, the Bosun broke out stores of painting stuff - paints, pallets, easels, smock and beret, and after an initial anti-rust treatment, the accommodation was given the usual pan-Atlantic attention by the crew and FID's. Here are several shots of the boys and girls at work on those handrails and bulkheads.

Legs on show
Legs on show
Legs on show



As can be seen, the ongoing painting program is being addressed and the ship should look pretty smart by the time it returns to the UK. It is these long passages that allow us to give the ship a facelift - which unfortunately our sister ship, RRS James Clark Ross is less and less able to do. Since she does an appreciable amount of science en route during the Pan-Atlantic crossing, it is not always possible for the crew to give attention to the cosmetic side of the ship maintenance. Not that RRS Ernest Shackleton is completely devoid of science on the Northern-bound leg. 'Two Beers' Garstecki (so named because a particular barman could not properly pronounce his christian name 'Tobias'), is busy in the wet lab doing some sub-culturing of samples extracted out of Antarctica, and then the ship has an ongoing program of magnetometer data logging whenever she is at sea.

The Bump - Click to enlargeThis week we were treated to an 'anomaly' as the ship 'bumped' over the join between the warm waters of South America and the cooler waters of the South Atlantic. Here we can definitely see the 'bump' as the ship jumped over the convergence!! See Magnetometer screendump at position 28°38'0 South 046° 54' 3 West. (But don't believe all you read in the pages). Click on image to enlarge the photo and see the 'bump'.




A Little About The Science

Magnetometer planes Referring back to the 18th March 2001 diary entry, there is an excellent explanation of Low Powered Magnetometers by Jim Fox. But basically, the 3 component Magnetometer onboard our ship, measures the magnetic field strengths in 3 planes. An 'x', 'y', and 'z' plane. The diagram here best describes how it is done.

For further information, see the Geophysical Database




Wavey-Davey's Weekly Whit-spot

For months, the crew of the Ernest Shackleton have had to put up with the inane jokes and jests of Wavey-Davey Taylor, so equally why should not the readership suffer? It is hoped that we can feature Wavey-Davey's joke page every week, but we fear that there are not enough......(WEEKS !!)

Your first offering :
Davey says - "Did you hear about the man who drowned one morning while eating his morning muesli ???"

"....a strong currant pulled him in !! "

Back to the Painting, and Charlie's team spent all of the week painting anything that didn't move - and a few things that did ! Once the ships searchlights and fast-launch lifebuoy holders had been subject to the FID's painting, - they had to be freely 'exercised' to free them from the iron-like grip of the paintjob. But the net results of all their work was plain to see when on Sunday they took an afternoon to go sunbathing on the helideck and the ship was starting to shine from all the white paint. Here we see a fine example of painting on the superstructure......artist unknown.

Any colour you like...so long as it's white! The Artists - Click to enlarge


Above: Left - "Any colour you like Ma'am, - so long as it's white" and right - The Artists (click on this image to enlarge).


"Times Change", it has been said, and never truer than on a ship going across the time zones of the world. We moved clocks again this week - TWICE. From leaving Stanley on GMT - 4 hours, we put the ship's clocks forward one hour to GMT - 3 last Sunday. The implications of this were immediately apparent when at 0600am each morning, there was NO SUN. Daylight did not creep over the horizon until 0630-0700 hours. It was strange to come up to a blackened bridge for morning coffee. During the course of the week however, and the course of our travel towards the equator, the sunrise occurred earlier and earlier until we could have morning coffee on the bridge in a glorious sunrise. Even a further time change to GMT - 2 had little effect on the light levels at breakfast time. I believe sunrise on the bridge was 0650 this morning, with twilight occurring in advance of that.


Talking, of things nautical, we had the 2nd Officer Alan out this week under the blinding sun to take navigational positions with 'sextant'. Just like they used to do in the old days. Here is Alan himself to give a brief discussion on the art of taking a sight.

* Meridian - any line joining the North and South Poles.

Until the early 1800's a ship's position at sea could not be determined with any real degree of certainty. Although latitude (how far North or South of the equator you are) could easily be found, longitude (how far East or West of the Greenwich Meridian you are) was a huge problem. Ships were regularly wrecked because of it. Small, remote islands could only be found by sailing on the correct parallel of latitude. Should the island be 'missed' literally, by even a small error in ascertaining the latitude, the crew faced starvation whilst the ship vainly sailed to and fro'.

The UK Admiralty became so concerned with these losses that they put up a reward for 'a method of reading, determining longitude at sea', and set up a committee called the 'Longitude Board'. A man named Harrison, a cabinet maker by trade, came up with the idea that the problem could be resolved by using a chronometer ( a very accurate clock). The theory was that if you know the time the sun crosses the Prime Meridian at Greenwich (1200 GMT) then by establishing the time the sun crosses the observer's Meridian, you could ascertain the angular distance the sun has moved in that time. ie. your longitude. The calculation involves a bit more than that, but that is the principle of the thing. If the Earth rotates through 360 degrees per day, then for each hour prior to and after 1200, the sun will appear to have moved through 15 degs. ie. if the sun crossed your Meridian at 1500 GMT you are at longitude 045° W, 0930 GMT you are at 037°30' E.

In this day and age of quartz watches, we are able to take so completely for granted the possession of a completely accurate timepieces, but in olden days, this was not the case. Accurate timekeeping was possible on dry land and Harrison, in fact, built a timepiece out of wood ! He used lignum vitae wood - almost as hard as steel - and that was in the 1700's.

The real difficulty was accurate timekeeping at sea. When subjected to the rigours of a creaking, rolling, pitching, sailing ship-of-the-line, the frail springs and pendulum were gradually rocked into a different time of day altogether.

Harrison set about designing a clock that could manage this. Presenting his mechanical solution to the Longitude Board he was more or less laughed at. No wonder - how could the establishment of the day be confounded by a problem affecting all of mankind, only to have it promptly resolved by an unheard-of working-class cabinet maker !

Their view was that the heavens would provide the answer. Indeed there was a method being researched at the time, by eminent astrologers (including the renowned Galileo - that was how big the problem was) using the moons of the planet Venus. The problem with this idea was many-fold: You can only see Venus when you're stood on the right side of the planet. You can only see Venus if there is no cloud - as it's rather a long way to Venus. You also need a steady platform to be able to see the moons, ie dry land. If you satisfy all 3 of these criteria, you now face an arduous spell of leafing through volumes of tables to find your longitude. In other words, this method was to prove impractical.

Harrison, against all odds, finally convinced the Admiralty of the suitability of his idea. He built the H1 to prove the theory worked, then H2, H3 and H4 were built in successful attempts to reduce it in size. The H4 fit into the hand ! Bear in mind that the building of these took decades. Each time he produced a chronometer, the Admiralty failed to pay up - claiming in their defence that at anytime he produced only 'one' chronometer and therefore had not met their stipulation of 'readily' available means. It wasn't until Harrison was a frail old gentleman that the Admiralty begrudgingly gave him his reward for effectively producing the greatest invention since the wheel !

Fixing the position at sea by stars, planets and the sun is done by using an instrument for measuring angles. It is called a 'sextant' (so called as it's graduated arc (or scale) is about 1/6 of a circle). It works on the principle that if a ray of light is reflected twice in the same plane, then the angle between the first and last directions of the ray is twice the angle between the mirrors.

To establish your position you will need :

  • A chronometer
  • A sextant
  • A person skilled in the use (and care) of both

All heavenly bodies are projected on to an imaginary sphere of infinite radius, called the celestial sphere. On earth, latitude and longitude are used to describe position. For heavenly bodies, we use GHA (Greenwich How Angle) in lieu of longitude and DEC (Declination) in lieu of latitude.

In stopping the chronometer (ie noting the exact time GMT) we effectively 'stop' the movement of the heavens - allowing us to establish our bearing from the planet, star, sun in use. We then need to measure our range (distance) from it using the sextant. We get an angular range from the horizon. This is corrected for:

  • error on the sextant - index error - if any
  • the height of the observer's eye above the sea level
  • refraction in the earth's atmosphere, where light rays are 'refracted' towards the denser layers - ie. when you look at a star, you see the 'refracted image' not the start itself which would be a little closer to the horizon.

We can also calculate this 'angular range'. Ironically, the accuracy of this latter option depends on the accuracy of the position you used to determine it !! When we compare the two altitudes obtained we (no surprise) get a difference. This we call an 'intercept' and we plot this either towards or away from the bearing of the sun (or other heavenly body in use).

You are now left with an item of monumental significance. It is called a 'position line'. You are on this line somewhere. Because this position line is part of a huge circle around the globe, you have to 'cross' it with another position line to find your actual position. The term we use for this whole procedure is a 'Celestial Running Fix'. 'Celestial' because it is not a terrestrial body that we use, 'Running' because we must move along the first position line up to the second to get a fix. The 'fix' is your actual determined position.

Intercept Plot - Click to enlarge
Taking a sighting - Click to enlarge


On a good day, a ship can expect to be able to get 3 positions a day - morning, evening starts and the noon position. Most of the Calculation below should now have some significance. (Saturday 04th May Celestial Running Fix).

Item

Position

Remarks

GMT

12. 25. 55

09:25.55 local time

Sextant Altitude

39° 30' 0

What was read from Sextant

Index Error (on)

- 10' 2

Amount of sextant error

Observed Altitude

39° 18' 8

 

DIP for 14.8m

- 6.8

Correction for Ht above s/level

Apparent Altitude

39° 12' 0

 

Total Correction

15.1

Correction for Atmospheric ref

True Altitude

39° 48.1

Angular distance from (*sun) ?

Call Altitude

39° 46. 3

Distance from (*sun)?

Intercept

1' 8 (T)

The amount of calculated distance is in error by :0

GHA

0° 48' 8

Angle between sun/Greenwich

Increments

6° 28' 8

Increments 25 mins 55 secs

GHA (total)

7° 17' 6

Total Angle

'+E / -W Longitude

040°39.3 (w)

Longitude from DR position

LHA

326° 38.3

Angle between me and the sun (measured west)

Declination

N 15° 59' 7

Sun's Latitude

D (0.7) incr

0.3

Increment of 25 mins 55 secs

DEC

N 16°00.0

Total declination.



The ways of navigating - Click to enlargePresented by the Navigating Officer : Alan Click on the image to enlarge - the ways and means of navigating a ship. The old and the new.



We also had Douglas , the 3rd Officer out there in the blinding sun, equally to ascertain the position of the ship, and here is Doug to explain how he did it with the use of the more 'modern day' equivalent of the sextant, - the G.P.S......

Global Positioning System. Doug says, just turn it on and read the screen. (If that doesn't work - only then go for the sextant)!

Presented by the 'cheating' Officer : Doug


Forthcoming events: Journey onwards to Grimsby.

Contributors this week : Many thanks to Rob correcting the Web Editor with regards to temperatures - and A HAPPY BIRTHDAY ROB, from your fellow officers and crew on board. Thanks to Wavey-Davey for his joke of the week and to the Weather Gods for being kind to us so far this voyage.

Thanks to Alan 'Navs' Newman for his insight into the art of taking a nautical 'sight', and to Dougie Leask for explaining an easier way to do it!!! By way of an acknowledgement, Alan would like to proffer his thanks to Mr.John Archer / college lecturer who gives his utmost to his students!

Diary 30 will be written on 12th May 2002 and should be published on 13th May 2002


Steve B
ETO(Comms)